Note: Descriptions are shown in the official language in which they were submitted.
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PROGRAMMABLE DIGITAL UP-CONVERSION FOR CONCURRENT
MULTI-BAND SIGNALS
Related Applications
[0001] This application claims the benefit of provisional patent
application
serial number 61/611,892, filed March 16, 2012, and non-provisional patent
application serial number 13/490,801, filed June 7, 2013, the disclosures of
which are hereby incorporated herein by reference in their entireties.
Field of the Disclosure
[0002] The present disclosure relates to digital up-conversion and more
particularly digital up-conversion for a concurrent multi-band signal.
Backaround
[0003] Traditionally, baseband to radio frequency (RF) up-conversion is
performed in the analog domain with one of three types of architectures,
namely,
a heterodyne architecture, a super-heterodyne architecture, or a direct
conversion architecture. Analog up-conversion architectures and previous
attempts at digital up-conversion architectures have generally been frequency
dependent in that they only operate over a small frequency band. In other
words,
a traditional analog up-converter that is designed for one frequency band will
not
operate effectively for a different frequency band. For example, an up-
converter
designed for operation at 800 megahertz (MHz) will not operate properly at 450
MHz, 1.5 GHz, or 1.9 gigahertz (GHz). Therefore, it is not possible for a
radio
designed for use in one frequency band to be converted for use in an alternate
frequency band without physically replacing an up-converter in the radio with
a
newly designed up-converter for the alternate frequency band or having
multiple
up-converters each capable of operating in a different frequency band. Either
option adds an increase to the cost of a system. Another disadvantage of an
analog up-converter is that it is subject to issues related to analog
variability such
as, but not limited to, component to component variability, temperature
variability,
voltage variability, and variability due to aging.
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[0004] A flexible, programmable digital up-conversion system that
addresses
the issues above is described in commonly owned and assigned U.S. Patent
Application Publication No. 2010/0098191 Al, entitled METHODS AND
SYSTEMS FOR PROGRAMMABLE DIGITAL UP-CONVERSION, filed on
October 20, 2008, and published on April 22, 2010, which is hereby
incorporated
herein by reference in its entirety.
[0005] Further issues arise when up-converting for a concurrent multi-
band
signal. For instance, while the digital up-conversion system of U.S. Patent
Application Publication No. 2010/0098191 Al can be used for concurrent multi-
band signals, it must treat the concurrent multi-band signal as a single wide-
band
signal. However, due to the large bandwidth of a concurrent multi-band signal,
treating the concurrent multi-band signal as a single wide-band signal may
exceed or approach processing capabilities of current Application Specific
Integrated Circuit (ASIC) and Field Programmable Gate Array (FPGA)
technology. Thus, there is a need for a digital up-conversion system for a
concurrent multi-band signal that also addresses the other issues discussed
above.
Summary
[0006] Systems and methods are disclosed for digital up-conversion of a
concurrent multi-band signal. As used herein, a "concurrent multi-band signal"
is
a signal that contains frequency components occupying multiple frequency bands
(i.e., a first continuous frequency band, a second continuous frequency band,
etc.) with no frequency components between adjacent frequency bands. In
general, the systems and methods disclosed herein make use of complex tuning
at baseband, up-sampling, and digital filtering to create a flexible digital
up-
conversion system for a concurrent multi-band signal.
[0007] In one embodiment, a digital up-conversion system for a
concurrent
multi-band signal includes multiple digital up-converter chains, each for a
different frequency band of the concurrent multi-band signal, and a digital
combiner that combines up-converted signals output by the digital up-converter
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chains to provide a combined digital signal. The combined digital signal is
processed by one or more additional processing components including a digital-
to-analog converter (DAC) to provide the concurrent multi-band signal.
[0008] In one embodiment, one or more parameters of the digital up-
converter
chains are configured based on an effective sampling rate of the DAC such
that,
after processing by the one or more additional processing components, complex
digital baseband signals for the frequency bands of the concurrent multi-band
signal are up-converted to desired carrier frequencies of the corresponding
frequency bands of the concurrent multi-band signal. In another embodiment,
the effective sampling rate of the DAC is configured based on one or more
predefined parameters of the digital up-converter chains such that, after
processing by the one or more additional processing components, complex
digital baseband signals for the frequency bands of the concurrent multi-band
signal are up-converted to desired carrier frequencies of the corresponding
frequency bands of the concurrent multi-band signal.
[0009] In one embodiment, each digital up-converter chain includes one
or
more digital up-converter stages and a digital quadrature modulator. For each
digital up-converter chain, the one or more digital up-converter stages of the
digital up-converter chain process a complex baseband signal for the
corresponding frequency band of the concurrent multi-band signal to produce an
output signal that includes an image of the complex baseband signal centered
at
a desired output frequency for the one or more digital up-converter stages.
The
digital quadrature modulator then processes the output signal of the one or
more
digital up-converter stages to provide the up-converted signal output by the
digital up-converter chain. In the frequency domain, the digital quadrature
modulation of the output signal results in frequency translating, or frequency-
shifting, the image of the complex baseband signal to a desired up-conversion
frequency for the digital up-converter chain. The desired up-conversion
frequencies for the digital up-converter chains are such that, after
processing of
the combined signal by the one or more additional processing components
including the DAC, images of the complex baseband signals are centered at the
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desired carrier frequencies of the corresponding frequency bands of the
concurrent multiband signal.
[0010] In another embodiment, each digital up-converter chain includes
one
or more digital up-converter stages. For each digital up-converter chain, the
one
or more digital up-converter stages of the digital up-converter chain process
a
complex baseband signal for the corresponding frequency band of the concurrent
multi-band signal to produce the up-converted signal output by the digital up-
converter chain such that the up-converted signal includes an image of the
complex baseband signal centered at a desired up-conversion frequency for the
digital up-converter chain. The desired up-conversion frequencies for the
digital
up-converter chains are such that, after processing of the combined signal by
the
one or more additional processing components including a digital quadrature
modulator followed by the DAC, images of the complex baseband signals are
centered at center frequencies of the corresponding frequency bands of the
concurrent multiband signal.
[0011] Further, in one embodiment, each complex up-converter stage of
each
digital up-converter chain includes a complex baseband tuner followed by an up-
sampler and an image selection filter. For each digital up-converter chain, a
baseband tuning frequency of the complex baseband tuner and a tuning
frequency of the image selection filter for at least one of the complex up-
converter stages in the digital up-converter chain are selected based on the
effective sampling rate of the DAC such that, after processing of the combined
signal by the one or more additional processing components including the DAC,
an image of the complex baseband signal input to the digital up-converter
chain
is centered at a desired carrier frequency of the corresponding frequency band
of
the concurrent multi-band signal. In another embodiment, one or more
parameters of the one or more additional processing components (e.g., the
effective sampling rate of the DAC) are configured based on predetermined
tuning frequencies of the image selection filters in the digital up-converter
chains,
and subsequently baseband tuning frequencies of the complex baseband tuners
are determined such that, after processing of the combined signal by the one
or
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more additional processing components including the DAC, images of the
complex baseband signals input to the digital up-converter chains are centered
at
desired carrier frequencies of the corresponding frequency bands of the
concurrent multi-band signal.
5 [0012] Those skilled in the art will appreciate the scope of the
present
disclosure and realize additional aspects thereof after reading the following
detailed description of the preferred embodiments in association with the
accompanying drawing figures.
Brief Description of the Drawing Figures
[0013] The accompanying drawing figures incorporated in and forming a
part
of this specification illustrate several aspects of the disclosure, and
together with
the description serve to explain the principles of the disclosure.
[0014] Figure 1 illustrates a digital up-conversion system for a
concurrent
multi-band signal according to one embodiment of the present disclosure;
[0015] Figures 2A through 2M are frequency domain diagrams that
graphically illustrate the operation of the digital up-conversion system of
Figure 1
according to one embodiment of the present disclosure;
[0016] Figure 3 illustrates a digital up-conversion for a concurrent
multi-band
signal that is similar to that of Figure 1 but where each digital up-converter
chain
can include multiple complex digital up-converter stages according to another
embodiment of the present disclosure;
[0017] Figure 4 is a flow chart illustrating the operation of the
digital up-
conversion systems of Figures 1 and 3 according to one embodiment of the
present disclosure;
[0018] Figure 5 is a flow chart that illustrates a process for
configuring the
digital up-conversion systems of Figures 1 and 3 according to one embodiment
of the present disclosure;
[0019] Figure 6 illustrates a digital up-conversion for a concurrent
multi-band
signal that is similar to that of Figures 1 and 3 but where an additional
combined
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up-converter performs further up-conversion of the combined signal according
to
another embodiment of the present disclosure;
[0020] Figure 7 illustrates a digital up-conversion system for a
concurrent
multi-band signal that is similar to that of Figure 1 but where digital
quadrature
modulation is performed after, rather than before, digitally combining outputs
of
the digital up-converter chains according to another embodiment of the present
disclosure;
[0021] Figures 8A through 8L are frequency domain diagrams that
graphically
illustrate the operation of the digital up-conversion system of Figure 7
according
to one embodiment of the present disclosure;
[0022] Figure 9 illustrates a digital up-conversion for a concurrent
multi-band
signal that is similar to that of Figure 7 but where each digital up-converter
chain
can include multiple complex digital up-converter stages according to another
embodiment of the present disclosure;
[0023] Figure 10 is a flow chart illustrating the operation of the digital
up-
conversion systems of Figures 7 and 9 according to one embodiment of the
present disclosure; and
[0024] Figure 11 illustrates a digital up-conversion for a concurrent
multi-band
signal that is similar to that of Figures 7 and 9 but where an additional
combined
up-converter performs further up-conversion of the combined signal according
to
another embodiment of the present disclosure.
Detailed Description
[0025] The embodiments set forth below represent the necessary
information
to enable those skilled in the art to practice the embodiments and illustrate
the
best mode of practicing the embodiments. Upon reading the following
description in light of the accompanying drawing figures, those skilled in the
art
will understand the concepts of the disclosure and will recognize applications
of
these concepts not particularly addressed herein. It should be understood that
these concepts and applications fall within the scope of the disclosure and
the
accompanying claims.
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[0026] Figure 1 illustrates a programmable concurrent multi-band digital
up-
conversion system 10 according to one embodiment of the present disclosure. In
general, the digital up-conversion system 10 operates to digitally up-convert
a
number (M) of complex baseband digital signals (Ii, 01 through Im, QM) to
provide
a concurrent multi-band signal (SmB). As used herein, a concurrent multi-band
signal, such as the concurrent multi-band signal (SmB), is a signal that
contains
frequency components occupying multiple frequency bands (i.e., a first
continuous frequency band, a second continuous frequency band, etc.) with no
frequency components between adjacent frequency bands. These frequency
bands are referred to herein as "frequency bands" of the concurrent multi-band
signal. In one embodiment, the concurrent multi-band signal includes two
frequency bands and, as such, is also referred to herein as a concurrent dual-
band signal.
[0027] For each frequency band of the concurrent multi-band signal, a
center
frequency of the frequency band is referred to herein as a carrier frequency
of
the concurrent multi-band signal. As such, the concurrent multi-band signal as
defined herein includes multiple carrier frequencies. Frequency differences
between adjacent carrier frequencies of the concurrent multi-band signal are
referred to herein as carrier frequency spacings. A ratio of the carrier
frequency
spacing over a maximum individual baseband bandwidth (i.e., the maximum
individual baseband bandwidth is a maximum bandwidth among the baseband
signals that correspond to the frequency bands of the concurrent multi-band
signal) is high such that a distortion or predistortion surrounding each of
the
carrier frequencies also occupies disjoint frequency bands. Some examples of
situations or applications where such concurrent multi-band signals are used
include multi-standard systems where each standard occupies a different
frequency band, systems that transmit signals for multiple standards
simultaneously, and systems having concurrent transmissions in multiple
frequency bands for the same standard.
[0028] The digital up-conversion system 10 includes M digital up-converter
chains 12-1 through 12-M, where again M is the number of frequency bands in
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the concurrent multi-band signal (SmB) and is greater than or equal to 2. The
digital up-converter chains 12-1 through 12-M may also be generally referred
to
herein collectively as digital up-converter chains 12 or individually as a
digital up-
converter chain 12. Each of the digital up-converter chains 12-1 through 12-M
performs digital up-conversion for a different one of the frequency bands of
the
concurrent multi-band signal (SmB). More specifically, the digital up-
converter
chain 12-1 digitally up-converts the complex baseband digital signal (I1, Qi)
for a
first frequency band of the concurrent multi-band signal (SmB) to provide a
corresponding up-converted digital signal (Sup_i). Likewise, the digital up-
converter chain 12-M digitally up-converts the complex baseband signal (Im,
QM)
for an Mth frequency band of the concurrent multi-band signal (SmB) to provide
a
corresponding up-converted digital signal (Sup_m).
[0029] The digital up-converter chains 12-1 through 12-M include
corresponding complex digital up-converter stages 14-1 through 14-M (generally
referred to herein collectively as complex digital up-converter stages 14 and
individually as complex digital up-converter stage 14) and corresponding
digital
quadrature modulators 16-1 through 16-M (generally referred to herein
collectively as digital quadrature modulators 16 and individually as a digital
quadrature modulator 16). In this embodiment, each of the digital up-converter
chains 12 includes one complex digital up-converter stage 14. However, as
discussed below, one or more or even all of the digital up-converter chains 12
may include one or more additional complex digital up-converter stages.
[0030] As illustrated, the complex digital up-converter stages 14-1
through 14-
M include complex baseband tuners 18-1 through 18-M, up-samplers 20-1
through 20-M, and image selection filters 22-1 through 22-M, respectively,
which
are also generally referred to herein as complex baseband tuners 18, up-
samplers 20, and image selection filters 22. Looking first at the complex
digital
up-converter stage 14-1 of the digital up-converter chain 12-1, the complex
baseband tuner 18-1 first performs a complex tuning of the complex baseband
digital signal (Ii, Qi) for the first frequency band of the concurrent multi-
band
signal (SmB). Preferably, a sampling rate of the complex baseband digital
signal
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(Ii, Qi) is fs/N. Alternatively, sampling rate conversion may be utilized to
convert
the sampling rate of the complex baseband digital signal (I1, Qi) to fs/N
prior to
complex baseband tuning. Note that if rate conversion is needed, the rate
conversion may alternatively be performed elsewhere in the digital up-
conversion
system 10 prior to a digital-to-analog converter (DAC) 26 (e.g., subsequent to
the
complex baseband tuner 18-1, subsequent to the up-sampler 20-1, subsequent
to the image selection filter 22-1, subsequent to the digital quadrature
modulator
16-1, or prior to the DAC 26).
[0031] As discussed below in detail, the complex baseband tuner 18-1
tunes
the complex baseband digital signal (I1, Qi) to a baseband tuning frequency
(IBBT_1) to thereby produce a complex tuned digital signal (IBBT_1, QBBT_1).
In one
embodiment, the baseband tuning frequency (IBBT_1) is programmable or
otherwise selectable within a range of ¨fs/2N and fs/2N, as discussed below in
detail, where fs is an effective sampling rate of the DAC 26 and N is an up-
sampling rate of the up-sampler 20-1. The complex baseband tuner 18-1 is
preferably utilized to provide fine tuning to achieve the desired carrier
frequency
for the corresponding frequency band of the concurrent multi-band signal. A
particular example of a complex baseband tuner is described in commonly
owned and assigned U.S. Patent Application Publication No. 2009/0316838 Al,
entitled CORDIC BASED COMPLEX TUNER WITH EXACT FREQEUNCY
RESOLUTION, filed on June 23, 2008 and published on December 24, 2009, is
hereby incorporated herein by reference in its entirety.
[0032] The up-sampler 20-1 up-samples the complex tuned digital signal
(IBB-n, QBBT_1) at an up-sampling rate N, where N 2, to produce an up-sampled
digital signal (lus_i, Qus_i) having a sampling rate of fs. In the frequency
domain,
the up-sampled digital signal (lus_i, Qus_i) includes N images of the complex
tuned digital signal (IBBT_
1,
QBBT_1) equally spaced apart in the frequency range of
0 to fs, where fs is the effective sampling rate of the DAC 26. The up-sampler
20-1 is preferably utilized to provide coarse tuning to achieve the desired
carrier
frequency for the corresponding frequency band of the concurrent multi-band
signal. The image selection filter 22-1 filters the up-sampled digital signal
(lus_i,
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Qus_i) to select a desired one of the images of the complex tuned digital
signal
(IBB-n, QBBT_1) and thereby provide a complex output signal of the complex
digital
up-converter stage 14-1 (bull, Qour_i). More specifically, the image selection
filter 22-1 is preferably programmable via one or more parameters (e.g.,
filter
5 coefficients) such that a passband of the image selection filter 22-1 is
centered at
a desired filter tuning frequency (fFILTERTUNING_1). The filter tuning
frequency
(fFILTERTUNING_1) is selected such that the desired image of the complex tuned
digital signal (113BL1, QBBT_1) falls within the passband of the image
selection filter
22-1.
10 [0033] The digital quadrature modulator 16-1 performs quadrature
modulation
on the complex output signal (bull, Qour_i) to provide the up-converted
digital
signal (Sup_i) output by the digital up-converter chain 12-1. In the frequency
domain, quadrature modulation results in frequency translating, or frequency-
shifting, the image of the complex tuned digital signal (113BL1, QBBT_1) in
the
complex output signal (lour_i, Qour_i) by fQmoD, where fQmoD is a modulation
frequency of the digital quadrature modulator 16-1, and converting the complex
signal into a real signal. Note, however, that fQmoD may be any frequency
including zero. In one preferred embodiment, fQmoD is equal to fs/4. In
another
embodiment, fQmoD is equal to zero in which case there is no frequency
translation of the image of the complex tuned digital signal (IBBT_1, QBBT_1)
in the
complex output signal (lour_i, Qour_i). It should be further noted that fQmoD
= 0
takes just the real component of the complex output, where the imaginary part
may need to be previously inverted depending on the desired sign of the
quadrature modulation. The frequency-translated image of the complex tuned
digital signal (113BL1, QBBT_1) is centered at a desired up-conversion
frequency for
the digital up-converter chain 12-1.
[0034] Similarly, regarding the complex digital up-converter stage 14-M
of the
digital up-converter chain 12-M, the complex baseband tuner 18-M first
performs
a complex tuning of the complex baseband digital signal (IM, QM) for the Mth
frequency band of the concurrent multi-band signal (SmB). Preferably, a
sampling
rate of the complex baseband digital signal (IM, QM) is fs/N. Alternatively,
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sampling rate conversion may be utilized to convert the sampling rate of the
complex baseband digital signal (Im, QM) to fs/N prior to complex baseband
tuning. Note that if rate conversion is needed, the rate conversion may
alternatively be performed elsewhere in the digital up-conversion system 10
prior
to the DAC 26 (e.g., subsequent to the complex baseband tuner 18-M,
subsequent to the up-sampler 20-M, subsequent to the image selection filter 22-
M, subsequent to the digital quadrature modulator 16-M, or prior to the DAC
26).
[0035] As discussed below in detail, the complex baseband tuner 18-M
first
performs a complex tuning of the complex baseband digital signal (Im, QM) for
the
Mth frequency band of the concurrent multi-band signal (SmB). As discussed
below in detail, the complex baseband tuner 18-M tunes the complex baseband
digital signal (Im, QM) to a baseband tuning frequency (fmr_m) to thereby
produce
a complex tuned digital signal (IBBT_M, QBBT_M). In one embodiment, the
baseband tuning frequency (IBBT_M) is programmable or otherwise selectable
within a range of ¨fs/2N and fs/2N, as discussed below in detail, where fs is
the
effective sampling rate of the DAC 26 and N is an up-sampling rate of the up-
sampler 20-M.
[0036] The up-sampler 20-M up-samples the complex tuned digital signal
(IBBTM, QBBT_M) at an up-sampling rate N, where N 2, to produce an up-
sampled digital signal (lus_m, Qus_m) having a sampling rate of fs. In the
frequency domain, the up-sampled digital signal (lus_m, Qus_m) includes N
images
of the complex tuned digital signal (IBBT Jib QBBT_M) equally spaced apart in
the
frequency range of 0 to fs, where fs is the effective sampling rate of the DAC
26.
The image selection filter 22-M filters the up-sampled digital signal (lus_m,
Qus_m)
to select a desired one of the images of the complex tuned digital signal
(IBBTM,
QBBT_M) and thereby provide a complex output signal (lourivi, Qour_m) of the
complex digital up-converter stage 14-M. More specifically, the image
selection
filter 22-M is preferably programmable via one or more parameters (e.g.,
filter
coefficients) such that a passband of the image selection filter 22-M is
centered
at a desired filter tuning frequency (fFILTERTUNING_M). The filter tuning
frequency
(fFILTERTUNING_M) is selected such that the desired image of the complex tuned
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digital signal (113BT_NA, QBBT_NA) falls within the passband of the image
selection filter
22-M.
[0037] The digital quadrature modulator 16-M performs quadrature
modulation on the complex output signal (lour_m, Qour_m) to provide the up-
converted digital signal (Sup_m) output by the digital up-converter chain 12-
M. In
the frequency domain, quadrature modulation results in frequency translating,
or
frequency-shifting, the image of the complex tuned digital signal (113BT_NA,
QBBT_NA)
in the complex output signal (lour_m, Qour_m) by fQmoD, where fQmoD is a
modulation frequency of the digital quadrature modulator 16-M, and converting
the complex signal into a real signal. Again, fQmoD can be any desired
frequency
including zero. Note that the modulation frequencies of the digital quadrature
modulators 16 may all be the same or, alternatively, one or more of the
digital
quadrature modulators 16 may have different modulation frequencies. The
frequency-translated image of the complex tuned digital signal (IBBrivi,
QBBT_M) is
centered at a desired up-conversion frequency for the digital up-converter
chain
12-M.
[0038] Notably, the digital quadrature modulators 16 may be configurable
to
operate on a definition of quadrature modulation as a+jb or a-jb. This may be
desirable because, for example, different cellular communication standards
(e.g.,
Code Division Multiple Access (CDMA) 2000 and 3rd Generation Partnership
Project (3GPP)) may define quadrature modulation differently. Therefore, in
order to accommodate different communication standards, the digital quadrature
modulator 16 may be configurable in this manner. Alternatively, this
configuration may be handled in the modem that generates the complex
baseband digital signals (Ii, 01 through Im, QM) by a complex conjugate
function
prior to the complex baseband tuners 18-1 through 18-M that can be activated
or
deactivated as needed, or in the analog domain (i.e., after the DAC 26) which
is
possible if there are two DACs 26, namely, one DAC 26 for I and one DAC 26 for
Q. Further, in one embodiment, the digital quadrature modulators 16 are
combined with the corresponding image selection filters 22.
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[0039] For more information regarding some example implementations of
the
complex baseband tuners 18, the up-samplers 20, the image selection filters
22,
and the digital quadrature modulators 16, the interested reader is directed to
commonly owned and assigned U.S. Patent Application Publication No.
2010/0098191 Al, entitled METHODS AND SYSTEMS FOR PROGRAMMABLE
DIGITAL UP-CONVERSION, filed on October 20, 2008 and published on April
22, 2010, which has been incorporated herein by reference in its entirety. For
example, while the up-sampler 20 and the image selection filter 22 of each
complex digital up-converter stage 14 may be implemented as separate
components, they are not limited thereto. The up-sampler 20 and the image
selection filter 22 may alternatively be implemented together as a polyphase
filter
that performs both up-sampling and image selection filtering.
[0040] The up-converted digital signals (Sup_i through Sup_m) are
combined
by a digital combiner 24 to provide a combined signal (ScomB). The DAC 26
receives the combined signal (ScomB) from the digital combiner 24 and converts
the combined signal (ScomB) to an analog signal (SpAc) at the effective
sampling
rate (fs) of the DAC 26. Notably, as used herein, a "digital" signal is a
discrete
time signal, whereas an "analog" signal is a continuous time signal. Further,
the
term "effective" is used to define that the DAC 26 may receive a signal input
having a sampling rate of fs or may receive multiple parallel inputs P, each
with a
sampling rate of fs/P, such that in combination the sampling rate processed by
the DAC 26 is fs. Such parallel inputs may be carried by, for example, one or
more higher rate serial links. When considering the frequency domain, digital-
to-
analog conversion by the DAC 26 also generates images of the spectrum
occurring between DC and fs repeatedly in the positive and negative frequency
directions. More specifically, the spectrum of DC to fs is repeated in the
positive
direction between fs and 2fs, 2fs and 3fs, etc. and in the negative frequency
direction between 0 and -fs, -fs and -2fs, -2fs and -3fs, etc.
[0041] In one embodiment, the effective sampling rate (fs) of the DAC 26
is
predetermined and potentially fixed. However, in another embodiment, the
effective sampling rate (fs) of the DAC 26 is configurable. In either case,
the
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effective sampling rate (fs) of the DAC 26 is preferably sufficient to at
least be
able to convert the concurrent multi-band signal (SmB) plus a separation
bandwidth between a first frequency band of the concurrent multi-band signal
(SmB) and a second frequency band of the concurrent multi-band signal (SmB).
[0042] The DAC 26 may be operated in a baseband mode (or more
generically a sinc mode) if it is desired to up-convert the signal to a
location in the
first Nyquist zone (i.e., frequency from DC to fs/2). A DAC operated in the
baseband mode has a frequency response that produces a useful output in the
first Nyquist zone. If the DAC 26 supports a radio frequency (RF) mode (or
more
generically a modified sinc mode), then the DAC 26 can be used to up-convert
the signal in the second Nyquist zone (i.e., frequency from fs/2 to fs), the
third
Nyquist zone (i.e., frequency from fs to 3fs/2), or possibly the fourth or
higher
Nyquist zone. In some embodiments, a DAC that supports an RF mode can do
so due to a configurable output stage adapted to modify the frequency response
of the DAC in the second and third Nyquist zones and/or higher Nyquist zones
to
be amenable to operation in these zones. The zone that is targeted will depend
on one or more factors, such as, but not limited to, the desired up-conversion
frequencies for the frequency bands of the concurrent multi-band signal (SmB),
the maximum sampling rate of the DAC 26, the performance capabilities of the
DAC 26, and the overall desired performance of the digital up-conversion
system
10.
[0043] An RF filter 28 filters the analog signal (SDAc) from the DAC 26
to
provide the concurrent multi-band signal (SmB). More specifically, the RF
filter 28
passes the images of the complex tuned digital signals (113BL1, QBBLi through
IBBT_NA, QBBT_NA) centered at the desired carrier frequencies of the frequency
bands
of the concurrent multi-band signal (SmB) while attenuating, or removing, the
remaining undesired images and frequency-flipped images of the complex tuned
digital signals (IBBT_
1, --, CD
13B-Li through IBBT_NA, QBBT_M)= For each frequency band of
the concurrent multi-band signal (SmB), the desired image may be below the
sampling rate fs of the DAC 26 (e.g., in the first or second Nyquist zones) or
above the sampling rate fs of the DAC 26 (e.g., in the third or higher Nyquist
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zone). The RF filter 28 may be implemented as a single concurrent multi-band
filter or, alternatively, the RF filter 28 may be implemented as a number of
parallel filters. More specifically, in one particular embodiment, a splitter
provides
the analog signal (SDAc) to each of M parallel filters, each configured to
provide
5 filtering for a corresponding frequency band of the concurrent multi-band
signal
(SmB). The resulting filtered signals are then combined to provide the
concurrent
multi-band signal (SmO=
[0044] Before proceeding, it should be noted that, while not
illustrated, other
components (e.g., rate change filter(s)) may be included in the digital up-
10 converter chains 12 and/or in the combined chain (i.e., the components
after the
digital combiner 24). Further, in some embodiments, the various components
may be in a different order than that illustrated in Figure 1. For example, in
an
alternative embodiment, the digital quadrature modulators 16 may be placed
between the complex baseband tuners 18 and the up-samplers 20. Also, in
15 some embodiments, some or all of the components of the digital up-
conversion
system 10 are implemented using one or more Field Programmable Gate Arrays
(FPGAs), one or more Application Specific Integrated Circuits (ASICs), or the
like, or any combination thereof.
[0045] As discussed below, in one embodiment, the baseband tuning
frequencies (IBB-r_i through IBBT_NA) and the filter tuning frequencies
(IFILTERTUNING_1
through IFILTERTUNING_NA) are selected based on a predetermined and
potentially
fixed effective sampling rate (Is) of the DAC 26 such that the complex
baseband
digital signals (Ii, 01 through INA, QM) are up-converted to the desired
carrier
frequencies of the concurrent multi-band signal (SmB). More specifically, the
baseband tuning frequencies (IBBLi through IBBLm) and the filter tuning
frequencies (fFILTERTUNING_1 through IFILTERTUNING_NA) are selected such that
images
of the complex baseband digital signals (Ii, 01 through Im, QM) in the up-
converted digital signals (Sup_i through Sup_m) are located at desired up-
conversion frequencies. The desired up-conversion frequencies are such that,
after further processing of the combined signal (ScomB) by the digital
combiner
24, the DAC 26, and the RF filter 28, images of the complex baseband digital
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signals (Ii, 01 through Im, QM) are located at the desired carrier frequencies
of the
corresponding frequency bands of the concurrent multi-band signal (SmB).
Alternatively, the effective sampling rate (Is) of the DAC 26 may be
configurable
and selected based on predetermined values for the filter tuning frequencies
(fFILTERTUNING_i through IFILTERTUNING_NA) and subsequently the baseband
tuning
frequencies (IBBLi through IBBT_Nn) are determined such that, after processing
of
the combined signal (ScomB) by the digital combiner 24, the DAC 26, and the RF
filter 28, images of the complex baseband digital signals (Ii, 01 through Im,
Om)
are located at the desired carrier frequencies of the corresponding frequency
bands of the concurrent multi-band signal (SmB).
[0046] Figures 2A through 2M are frequency-domain diagrams that
graphically illustrate the operation of the digital up-conversion system 10 of
Figure 1 for one example where the concurrent multi-band signal (SmB) is a
concurrent dual-band signal. Figures 2A through 2E illustrate the operation of
the digital up-converter chain 12-1 for the first band of the concurrent dual-
band
signal. As illustrated in Figure 2A, the complex baseband digital signal (Ii,
Qi) is
centered at DC. The complex baseband tuner 18-1 tunes the complex baseband
digital signal (Ii, Qi) to the baseband tuning frequency (IBBLi), as
illustrated in
Figure 2B. After up-sampling by the up-sampler 20-1, the up-sampled digital
signal (lus_i, Qus_i) includes N equally spaced images of the complex tuned
digital signal (IBBLi, QBBLi) between DC and fs, wherein in this example N=8,
as
illustrated in Figure 2C. The image selection filter 22-1 then filters the up-
sampled digital signal (lus_i, Qus_i) to select the desired image, as
illustrated in
Figure 2D. Finally, after digital quadrature modulation, the image in the
complex
output signal (lour_i, Qour_i) from the image selection filter 22-1 is
frequency
translated by a frequency of fQmoD, to provide the up-converted digital signal
(Sup_i), as illustrated in Figure 2E. In addition, because the up-converted
digital
signal (Sup_i) is a real signal, it also includes frequency-flipped images of
frequency-translated images.
[0047] Figures 2F through 2J illustrate the operation of the digital up-
converter
chain 12-M for the Mth band of the concurrent dual-band signal where for the
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concurrent dual-band signal M=2. As illustrated in Figure 2F, the complex
baseband digital signal (12, 02) is centered at DC. The complex baseband tuner
18-2 tunes the complex baseband digital signal (12, 02) to the baseband tuning
frequency (issr_2), as illustrated in Figure 2G. After up-sampling by the up-
sampler 20-2, the up-sampled digital signal (lus_2, Qus_2) includes N equally
spaced images of the complex tuned digital signal (Issr_2, Qssr_2) between DC
and fs, wherein in this example N=8, as illustrated in Figure 2H. The image
selection filter 22-2 then filters the up-sampled digital signal (lus_2,
Qus_2) to
select the desired image, as illustrated in Figure 21. Finally, after digital
quadrature modulation, the image in the complex output signal (lour_2, Qour_2)
from the image selection filter 22-2 is frequency translated by a frequency of
fomoD to provide the up-converted digital signal (Sup_2), as illustrated in
Figure 2J.
In addition, because the up-converted digital signal (Sup_2) is a real signal,
it also
includes frequency-flipped images of frequency-translated images.
[0048] Then, as illustrated in Figure 2K, the digital combiner 24 combines
the
up-converted digital signals (Sup_i and Sup_2) to provide the combined signal
(Scoms)= Next, the combined signal (Scorns) is digital-to-analog converted by
the
DAC 26 to provide the analog signal (SDAc) as illustrated in Figure 2L. As
shown,
the analog signal (SDAc) includes images of the spectrum occurring between DC
and fs repeatedly in the positive frequency direction. While not shown, the
images of the spectrum also occur repeatedly in the negative frequency
direction.
Lastly, the RF filter 28 selects images located at center frequencies (fci and
fo2)
of the frequency bands of the concurrent dual-band signal to thereby provide
the
concurrent dual-band signal, as illustrated in Figure 2M. Thus, by using
complex
baseband tuning, up-sampling, image selection filtering, and quadrature
modulation, images of the complex baseband digital signals (11, Qi and 12, 02)
are produced at the desired carrier frequencies of the concurrent dual-band
signal.
[0049] Figure 3 illustrates the digital up-conversion system 10
according to
another embodiment of the present disclosure. As illustrated, the digital up-
conversion system 10 is substantially the same as that of Figure 1. However,
in
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this embodiment, at least some of the digital up-converter chains 12-1 through
12-M include multiple complex digital up-converter stages. More specifically,
in
this example, the digital up-converter chain 12-1 includes the complex digital
up-
converter stage 14-1 as well as one or more additional complex digital up-
converter stages 30-1. The additional complex digital converter stage(s) 30-1
may be implemented like the complex digital up-converter stage 14-1 of Figure
1.
However, in this embodiment, up-sampling by the desired factor of N is split
between the up-samplers of the complex digital up-converter stages 14-1 and 30-
1.
[0050] In one embodiment, the baseband tuning frequencies and filter tuning
frequencies of the complex baseband tuners and image selection filters of the
complex digital up-converter stages 14-1 and 30-1 are determined based on the
effective sampling rate (fs) of the DAC 26 and the collective up-sampling rate
(N)
of the up-samplers such that the up-converted digital signal (Sup_i) includes
an
image of the complex baseband digital signal (I1, Qi) at the desired up-
conversion frequency for the first frequency band of the concurrent multi-band
signal (SmB). Alternatively, the filter tuning frequencies of the image
selection
filters of the complex digital up-converter stages 14-1 and 30-1 are
predetermined, and the effective sampling rate (fs) of the DAC 26 and
subsequently the baseband tuning frequencies of the complex baseband tuners
are configured such that, after further processing of the combined signal
(ScomB)
by the DAC 26 and the RF filter 28, an image of the complex baseband digital
signal (I1, Qi) is centered at the desired carrier frequency for the first
frequency
band of the concurrent multi-band signal (SmB).
[0051] Likewise, the digital up-converter chain 12-M includes the complex
digital up-converter stage 14-M as well as one or more additional complex
digital
up-converter stages 30-M. The additional complex digital converter stage(s) 30-
M may be implemented like the complex digital up-converter stage 14-M of
Figure 1. However, in this embodiment, up-sampling by the desired factor of N
is
split between the up-samplers of the complex digital up-converter stages 14-M
and 30-M.
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[0052] In one embodiment, the baseband tuning frequencies and filter
tuning
frequencies of the complex baseband tuners and image selection filters of the
complex digital up-converter stages 14-M and 30-M are determined based on the
effective sampling rate (fs) of the DAC 26 and the collective up-sampling rate
(N)
of the up-samplers such that the up-converted digital signal (Sup_m) includes
an
image of the complex baseband digital signal (Im, QM) at the desired up-
conversion frequency for the Mth frequency band of the concurrent multi-band
signal (SmB). Alternatively, the filter tuning frequencies of the image
selection
filters of the complex digital up-converter stages 14-M and 30-M are
predetermined, and the effective sampling rate (fs) of the DAC 26 and
subsequently the baseband tuning frequencies of the complex bandband tuners
are configured such that, after further processing of the combined signal
(ScomB)
by the DAC 26 and the RF filter 28, an image of the complex baseband digital
signal (Im, QM) is centered at the desired carrier frequency for the
corresponding
frequency band of the concurrent multi-band signal (SmB).
[0053] Figure 4 is a flow chart that illustrates the operation of the
digital up-
conversion system 10 of Figures 1 and 3 according to one embodiment of the
present disclosure. First, the complex baseband tuners 18-1 through 18-M
complex tune the complex baseband digital signals (Ii, 01 through Im, QM) to
produce the corresponding complex tuned digital signals (IBBLi, QBBT_i through
IBBTM, QBBT_M) (step 100). Next, the up-samplers 20-1 through 20-M up-sample
the complex tuned digital signals (IBBT_1, QBBT_i through 'BBTM, QBBT_M) to
produce the up-sampled digital signals (lus_i, Qus_i through lus_m, Qus_m)
(step
102). The image selection filters 22-1 through 22-M then select the desired
images in the up-sampled digital signals (lus_i, Qus_i through lus_m, Qus_m)
to
produce the complex output signals (lour_i, QOUT_i through lour_m, QOUT_M)
(step
104). Note that if there are additional complex digital up-converter stages 30-
1
through 30-M as in the embodiment of Figure 3, then steps 100 through 104 are
repeated for each of the additional complex digital up-converter stages 30-1
through 30-M.
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[0054] The digital quadrature modulators 16 then perform quadrature
modulation on the complex output signals (lour_i, Qour_i through lour_m,
QOUTM)
output by the complex digital up-converter stages 14-1/30-1 through 14-M/30-M
to provide the up-converted digital signals (Sup_i through Sup_m) (step 106).
The
5 digital combiner 24 then combines the up-converted digital signals (Sup_i
through
Sup_m) to provide the combined signal (ScomB) (step 108). The DAC 26 performs
digital-to-analog conversion of the combined signal (ScomB) to produce the
analog signal (ScAc) (step 110). Lastly, the analog signal (SDAc) is filtered
to
provide the concurrent multi-band signal (SmB) (step 112).
10 [0055] Additional method steps may also involve determining the
amount of
complex tuning for the complex tuning step and determining filter coefficients
used in the image selection filtering step. In some embodiments, an amount of
complex tuning used in the complex tuning step and filter coefficients used in
the
image selection filtering step are each determined as a function of a
15 predetermined and potentially fixed effective sampling rate (fs) of the
DAC 26
such that the up-converted digital signals (Sup_i through Sup_m) include
images of
the complex baseband digital signals (li, Qi through INA, QM) centered at the
desired up-conversion frequencies and, after digital-to-analog conversion and
RF
filtering of the combined signal (ScomB), images of the complex baseband
digital
20 signals (Ii, Qi through INA, QM) are located at the desired carrier
frequencies of the
corresponding frequency bands of the concurrent multi-band signal (SmB).
[0056] If the sampling rate of the complex baseband digital signals (li,
Qi
through INA, QM) is not fs/N, then re-sampling may be performed at some point
during the method to ensure that the signal input to the DAC 26 has an
effective
sample rate of fs. If the sample rate of the complex baseband digital signals
(Ii,
Qi through INA, QM) is not fs/N, then there may not be N images in the
bandwidth
between DC and fs as described in the example above. Rather, N images would
occur between DC and the sample rate of the complex baseband digital signals
(Ii, Qi through INA, QM) multiplied by N.
[0057] In some embodiments, up-sampling and image selection filtering are
implemented together as a polyphase filtering process. In some embodiments,
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quadrature modulation is implemented subsequent to, and in combination with,
the polyphase filtering process.
[0058] In some embodiments, the steps described above for performing up-
conversion may not be implemented in the particular order described and
illustrated in Figure 4. In some embodiments, digital quadrature modulation
may
be implemented subsequent to the complex baseband tuning of step 100 and
prior to the up-sampling of step 102.
[0059] As a result of the unique usage of complex tuning, the inherently
repetitive nature of sampled signals, and programmable digital filtering, some
embodiments of the method provide flexible digital up-conversion capable of
tunability over a wide frequency range. Having such a wide frequency range of
tunability, the method may be used for effectively re-banding a radio from one
set
of concurrent frequency bands to another set of concurrent frequency bands in
a
manner that is not possible with conventional analog radios. Whereas
conventional analog radios would typically need to be redesigned for different
sets of concurrent frequency bands, a radio implementing some embodiments of
the digital up-conversion system 10 disclosed herein can be easily
reconfigured
by providing the radio with information to change the operating parameters of
one or more programmable components such that when the operating
parameters are implemented the radio operates in the new set of frequency
bands. The method may be used to reconfigure a radio which has been
operating to provide a concurrent multi-band signal using one set of frequency
bands to operate to provide a concurrent multi-band signal using a different
set of
frequency bands without significant redesign of the components performing the
up-conversion function.
[0060] Figure 5 illustrates a process for configuring the digital up-
conversion
system 10 according to one embodiment of the present disclosure. In this
particular embodiment, the digital up-converter chains 12-1 through 12-M of
the
digital up-conversion system 10 are those of Figure 1. However, this process
may be extended to configure the digital up-converter chains 12-1 through 12-M
having multiple complex digital up-converter stages as shown in Figure 3.
First,
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a highest carrier frequency (fcH) and/or a lowest carrier frequency (fa) of
the
carrier frequencies of the concurrent multi-band signal are determined (step
200).
Next, the effective sampling rate (fs) of the DAC 26 is selected based on the
highest carrier frequency (fcH) and/or the lowest carrier frequency (fa) of
the
carrier frequencies of the concurrent multi-band signal (step 202). More
specifically, in one embodiment, the effective sampling rate (fs) is selected
such
that fs/2 < fa. In another embodiment, the effective sampling rate (fs) is
selected
such that fcH < fs. Note that while in this embodiment the highest carrier
frequency (fcH) and/or the lowest carrier frequency (fcL) of the carrier
frequencies
of the concurrent multi-band signal are determined prior to selecting the
effective
sampling rate (fs) of the DAC 26, the present disclosure is not limited
thereto. In
another embodiment, the effective sampling rate (fs) of the DAC 26 is selected
first. Then, carrier frequencies that are suitable for the digital up-
conversion
system 10 are determined based on the selected effective sampling rate (fs) of
the DAC 26.
[0061] Next, the filter tuning frequencies (fFILTERTUNING_i through
IFILTERTUNING_NA) are determined for the image selection filters 22-1 through
22-M
based on the effective sampling rate (fs) of the DAC 26 (step 204). In one
embodiment, step 202 is performed such that the effective sampling rate (fs)
of
the DAC 26 is predetermined and fixed. In another embodiment, the effective
sampling rate (fs) of the DAC 26 is configurable. The filter tuning
frequencies
(fFILTERTUNING_i through IFILTERTUNING_NA) are such that the images of the
complex
baseband digital signals (Ii, 01 through INA, QM), and more specifically the
complex baseband digital signals (Ii, 01 through Im, CM, produced at the
desired
up-conversion frequencies for the up-converted digital signals (Sup_i through
Sup_m) are selected or, in other words, passed by the image selection filters
22-1
through 22-M while the remaining images are attenuated, or removed.
[0062] Lastly, the baseband tuning frequencies (IBBLi through IBBT_NA)
of the
complex baseband tuners 18-1 through 18-M are determined based on the
effective sampling rate (fs) of the DAC 26 (step 206). Again, in one
embodiment,
step 202 is performed such that the effective sampling rate (fs) of the DAC 26
is
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predetermined and fixed. In another embodiment, the effective sampling rate
(fs)
of the DAC 26 is configurable. In general, the baseband tuning frequencies
(fmr_i through fmr_m) are select frequencies in the range of -fs/2N to fs/2N
such
that images of the complex baseband digital signals (Ii, 01 through Im, QM)
and
more specifically images of the complex tuned digital signals (113BL1, QBBT_1
through IBBT_NA, QBBT_NA) are produced at the desired up-conversion
frequencies
for the up-converted digital signals (Sup_i through Sup_m). The desired up-
conversion frequencies for the up-converted digital signals (Sup_i through
Sup_m)
are such that, after digital-to-analog conversion and RF filtering, images of
the
complex baseband digital signals (Ii, 01 through Im, Om) are located at the
carrier
frequencies of the corresponding frequency bands of the concurrent multi-band
signal (SNAB).
[0063] In one particular embodiment, for each frequency band X of the
concurrent multi-band signal (SmB), the baseband tuning frequency (IBBT_X) and
the filter tuning frequency (fFILTERTUNING_X) are determined as:
if (Liget X ¨ fqmod Eq. 1
f filtertuning _X = M d( ftarget_X fqmod' fs)
( filtertuning X ) Eq. 2
JS
f BBT X = mod f filtertuning X 1¨
\
(ftarget_X fqmod < Eq. 3
f filtertuning _X = (mod( f
¨ arg Cr _X ¨ fqmod fS, fS )) fS
(ffiltertuning X <0) Eq. 4
Js Js _Js
fBBT X = MOd f gfiltertunin X
N N } N }
where ftarget_X is the desired center frequency of the frequency band X of the
concurrent multi-band signal (SmB), fs is a predetermined and preferably fixed
effective sampling rate of the DAC 26, and N is the up-sampling rate of the up-
sampler 20-X. Practically, the complex baseband tuners 18-1 through 18-M are
implemented to tune over a range of -fs/2N to fs/2N. If the result of Eq. 2 or
Eq. 4
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is greater than the absolute value of Is/2N, it can be converted to the range
above by subtracting Is/N.
[0064] Once the baseband tuning frequencies (IBBT_i through IBBT_NA) and
the
filter tuning frequencies (fFILTERTUNING_1 through IFILTERTUNING_NA) are
determined,
the complex baseband tuners 18-1 through 18-M and the image selection filters
22-1 through 22-M are configured accordingly (step 208). The image selection
filters 22-1 through 22-M may be configured by, for example, providing
corresponding filter coefficients to the image selection filters 22-1 through
22-M.
The process of Figure 5 can be used perform a one-time configuration (e.g.,
during manufacturing). However, the process of Figure 5 is preferably used to
dynamically re-configure the digital up-conversion system 10 to accommodate
different concurrent multi-band signals (i.e., concurrent multi-band signals
having
different frequency bands).
[0065] Figure 6 illustrates the digital up-conversion system 10
according to
another embodiment of the present disclosure. In this embodiment, the digital
up-conversion system 10 further includes a combined up-converter 32 that
operates to provide additional up-conversion by a frequency (lcomB) subsequent
to the combining of the up-converted digital signals (Sup_i through Sup_m). In
this
embodiment, the up-conversion frequencies of the digital up-converter chains
12
are intermediate frequencies that provide sufficient frequency separation, and
the
combined up-converter 32 up-converts the combined signal (ScomB) to produce
an up-converted combined signal (Sup_comB)=
[0066] Figures 7 through 11 illustrate embodiments that are similar to
those of
Figures 1 through 6. However, in the embodiments of Figures 7 through 11,
digital quadrature modulation is performed subsequent to, rather than prior
to,
digitally combining the up-converted digital signals output by the digital up-
converter chains 12-1 through 12-M. More specifically, Figure 7 illustrates a
programmable concurrent multi-band digital up-conversion system 10 according
to another embodiment of the present disclosure. This embodiment is
substantially the same as that of Figure 1. However, in this embodiment, the
digital up-converter chains 12 do not include the digital quadrature
modulators
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16. Instead, the digital up-conversion system 10 includes a digital quadrature
modulator 34 that performs digital quadrature modulation after digitally
combining
complex outputs of the digital up-converter chains 12.
[0067] More specifically, as discussed above, the digital up-conversion
5 system 10 includes the M digital up-converter chains 12-1 through 12-M,
where
again M is the number of frequency bands in the concurrent multi-band signal
(SmB). Each of the digital up-converter chains 12-1 through 12-M performs
digital
up-conversion for a different one of the frequency bands of the concurrent
multi-
band signal (SmB). In this embodiment, the digital up-converter chain 12-1
10 digitally up-converts the complex baseband digital signal (I1, Qi) for a
first
frequency band of the concurrent multi-band signal (SmB) to provide a
corresponding complex up-converted digital signal (lup_i, Qup_i). Likewise,
the
digital up-converter chain 12-M digitally up-converts the complex baseband
digital signal (Im, QM) for an Mth frequency band of the concurrent multi-band
15 signal (SmB) to provide a corresponding complex up-converted digital
signal
(Iup_m, Qup_m).
[0068] The digital up-converter chains 12-1 through 12-M include the
complex
digital up-converter stages 14-1 through 14-M, respectively. In this
embodiment,
each of the digital up-converter chains 12 includes one complex digital up-
20 converter stage 14. However, as discussed below, one or more or even all
of the
digital up-converter chains 12 may also include one or more additional complex
digital up-converter stages. As illustrated, the complex digital up-converter
stages 14-1 through 14-M include the complex baseband tuners 18-1 through 18-
M, the up-samplers 20-1 through 20-M, and the image selection filters 22-1
25 through 22-M, respectively, as discussed above. However, unlike the
embodiment of Figure 1, the digital up-converter chains 12-1 through 12-M do
not include the digital quadrature modulators 16-1 through 16-M. In this
embodiment, the complex output signals output by the image selection filters
22-
1 through 22-M are referred to as complex up-converted digital signals (lup_i,
QUP_i through lup_m, Qup_m) output by the digital up-converter chains 12-1
through
12-M.
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[0069] The complex up-converted digital signals (lup_i, Qup_i through
lup_m,
Qup_m) are combined by a complex digital combiner 36 to provide a complex
combined signal (lcomB, QcomB). More specifically, the complex digital
combiner
36 includes a first digital combiner 38 that combines, or sums, in-phase
components (lup_i through lup_m) of the complex up-converted digital signals
(lup_i, Qup_i through lup_m, Qup_m) to provide an in-phase component (lcomB)
of
the complex combined signal (lcomB, QcomB). The complex digital combiner 36
also includes a second digital combiner 40 that combines, or sums, quadrature-
phase components (Qup_i through Qup_m) of the complex up-converted digital
signals (lup_i, Qup_i through lup_m, Qup_m) to provide a quadrature-phase
component (QcomB) of the complex combined signal (lcomB, QcomB).
[0070] The digital quadrature modulator 34 then performs quadrature
modulation on the complex combined signal (lcomB, QcomB) to provide a
quadrature modulated signal (SQmoD). In the frequency domain, quadrature
modulation results in frequency translating, or frequency-shifting, the
desired
images of the complex tuned digital signals (113B-1_1, QBBLi through IBBT_NA,
QBBT_NA)
in the combined complex signal (lcomB, QcomB) by fQmoD, where fQmoD is a
modulation frequency of the digital quadrature modulator 34, and converting
the
complex signal into a real signal. Again, fQmoD can be any desired frequency
including zero. Because the quadrature modulated signal (Swap) is a real
signal, the quadrature modulated signal (Swop) includes both the frequency-
translated images of the complex tuned digital signals (113BL1, QBBLi through
'BBTM, QBBT_NA) from the complex combined signal (lcomB, QcomB) and frequency-
flipped images of the frequency-translated images. Before proceeding, it
should
be noted that, in an alternative embodiment, the quadrature modulator 34 may
be
an analog quadrature modulator that follows the DAC 26 and is prior to the RF
filter 28, in which case there would be two DACs 26, namely, one DAC 26 for I
and another DAC 26 for Q.
[0071] The DAC 26 receives the quadrature modulated signal (SQmoD) from
the digital quadrature modulator 34 and converts it to the analog signal
(SbAc).
When considering the frequency domain, digital-to-analog conversion by the
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DAC 26 also generates images of the spectrum occurring between DC and fs
repeatedly in the positive and negative frequency directions. More
specifically,
the spectrum of DC to fs is repeated in the positive direction between fs and
2fs,
2fs and 3fs, etc. and in the negative frequency direction between 0 and -fs, -
fs
and -2fs, -2fs and -3fs, etc.
[0072] The RF filter 28 filters the analog signal (SDAc) from the DAC 26
to
provide the concurrent multi-band signal (SmB). More specifically, the RF
filter 28
passes the images of the complex tuned digital signals (113B1-_1) QBBT_i
through
'BBTM, QBBT_NA) in the digital-to-analog converted quadrature modulated signal
(SmoD) centered at the desired carrier frequencies of the frequency bands of
the
concurrent multi-band signal (SmB) while attenuating, or removing, the
remaining
undesired images and frequency-flipped images of the complex tuned digital
signals (113B1-_1, QBBT_i through IBBT_NA, QBBT_M). For each frequency band of
the
concurrent multi-band signal (SmB), the desired image may be below the
sampling rate fs of the DAC 26 (e.g., in the first or second Nyquist zones) or
above the sampling rate fs (e.g., in the third or higher Nyquist zone).
[0073] Figures 8A through 8L are frequency-domain diagrams that
graphically
illustrate the operation of the digital up-conversion system 10 for one
example
where the concurrent multi-band signal (SmB) is a concurrent dual-band signal.
Figures 8A through 8D illustrate the operation of the digital up-converter
chain
12-1 for the first band of the concurrent dual-band signal. As illustrated in
Figure
8A, the complex baseband digital signal (11, Qi) is centered at DC. The
complex
baseband tuner 18-1 tunes the complex baseband digital signal (11, Qi) to the
baseband tuning frequency (fBBT_1), as illustrated in Figure 8B. After up-
sampling
by the up-sampler 20-1, the up-sampled digital signal (lus_i, Qus_i) includes
N
equally spaced images of the complex tuned digital signal (113B1-_1, QBBT_1)
between DC and fs, wherein in this example N=8, as illustrated in Figure 8C.
The image selection filter 22-1 then filters the up-sampled digital signal
(lus_i,
Qus_i) to select the desired image and thereby provide the complex up-
converted
digital signal (lup_i, Qup_i), as illustrated in Figure 8D.
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28
[0074] Figures 8E through 8H illustrate the operation of the digital up-
converter chain 12-M for the Mth band of the concurrent dual-band signal where
for the concurrent dual-band signal M=2. As illustrated in Figure 8E, the
complex
baseband digital signal (12, 02) is centered at DC. The complex baseband tuner
18-2 tunes the complex baseband digital signal (12, 02) to the baseband tuning
frequency (issr_2), as illustrated in Figure 8F. After up-sampling by the up-
sampler 20-2, the up-sampled digital signal (lus_2, Qus_2) includes N equally
spaced images of the complex tuned digital signal (IBBT_2) QBBT_2) between DC
and fs, wherein in this example N=8, as illustrated in Figure 8G. The image
selection filter 22-2 then filters the up-sampled digital signal (lus_2,
Qus_2) to
select the desired image and thereby provide the complex up-converted digital
signal (lup_2, Qup_2), as illustrated in Figure 8H.
[0075] Then, as illustrated in Figure 81, the complex digital combiner
36
combines the up-converted complex digital signals (lup_i, Qup_i and 'UP 2,
QuP_2)
to provide the complex combined signal (Icoms, ()cans). The complex combined
signal (Icans, Qcoms) is quadrature modulated by the digital quadrature
modulator
34 to provide the quadrature modulated signal (Swop), as illustrated in Figure
8J. As shown in Figure 8J, as a result of the quadrature modulation, the
images
in the complex combined signal (Icans, Qcoms) are frequency translated by a
frequency fQmoD. In addition, because the quadrature modulated signal (Swop)
is a real signal, it also includes frequency-flipped images of frequency-
translated
images.
[0076] Next, the quadrature modulated signal (Swop) is digital-to-analog
converted by the DAC 26 to provide the analog signal (SDAc) as illustrated in
Figure 8K. As shown, the analog signal (SDAc) includes images of the spectrum
occurring between DC and fs repeatedly in the positive frequency direction.
While not shown, the images of the spectrum also occur repeatedly in the
negative frequency direction. Lastly, the RF filter 28 selects images located
at
carrier frequencies (fci and fc2) of the frequency bands of the concurrent
dual-
band signal to thereby provide the concurrent dual-band signal, as illustrated
in
Figure 8L. The RF filter 28 can be either a multi-band filter or a wide-band
filter.
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Multi-Nyquist zone operation is possible if the RF filter 28 passes the
desired
signal in different Nyquist zones. Thus, in order to allow filtering, the
image from
one Nyquist zone should not land on or near the desired signal in another
Nyquist zone. For example, if it is desired to transmit 728-746 MHz
simultaneously with 2110-2170 MHz, then fs = 2877 MHz does not work because
the images land on each other, but fs = 2500 MHz does work as the images are
330-390 MHz and 1745-1781 MHz which are both away from the desired
frequencies. By using complex baseband tuning, up-sampling, image selection
filtering, and quadrature modulation, images of the complex baseband digital
signals (Ii, 01 and 12, 02) are produced at the desired carrier frequencies of
the
concurrent dual-band signal.
[0077] Figure 9 illustrates the digital up-conversion system 10
according to
another embodiment of the present disclosure. As illustrated, the digital up-
conversion system 10 is substantially the same as that of Figure 7. However,
in
this embodiment, at least some of the digital up-converter chains 12-1 through
12-M include multiple complex digital up-converter stages 30-1 through 30-M,
as
described above with respect to Figure 3.
[0078] Figure 10 is a flow chart that illustrates the operation of the
digital up-
conversion system 10 of Figures 7 and 9 according to one embodiment of the
present disclosure. This embodiment is substantially the same as that of
Figure
4 but where digital quadrature modulation has been moved after digitally
combining the up-converted signals output by the digital up-converter chains
12-
1 through 12-M. First, the complex baseband tuners 18-1 through 18-M tune the
complex baseband digital signals (11, 01 through 1m, QM) to produce the
corresponding complex tuned digital signals (1BBT_1, QBBLi through IBBT_M,
QBBT_M) (step 300). Next, the up-samplers 20-1 through 20-M up-sample the
complex tuned digital signals (IBBT_1, QBBT_i through IBBT_M, QBBT_M) to
produce
the up-sampled digital signals (lus_i, Qus_i through lus_m, Qus_m) (step 302).
The
image selection filters 22-1 through 22-M then select the desired images in
the
up-sampled digital signals (lus_i, Qus_i through lus_m, Qus_m) to thereby
provide
the complex up-converted digital signals (lup_i, Qup_i through lup_m, Qup_m)
(step
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304). Note that if there are additional complex digital up-converter stages 30-
1
through 30-M as in the embodiment of Figure 9, then steps 400 through 404 are
repeated for each of the additional complex digital up-converter stages 30-1
through 30-M.
5 [0079] The complex digital combiner 36 then combines the complex
up-
converted digital signals (lup_i, Qup_i through lup_m, Qup_m) to provide the
complex combined signal (lcomB, QcomB) (step 306). The complex combined
signal (lcomB, QcomB) is quadrature modulated to provide the quadrature
modulated signal (Swop) (step 308). The DAC 26 performs digital-to-analog
10 conversion of the quadrature modulated signal (Swop) to produce the
analog
signal (SDAc) (step 310). Lastly, the analog signal (SDAc) is filtered to
provide the
concurrent multi-band signal (SmB) (step 312).
[0080] Notably, in one embodiment, the digital up-converter chains 12-1
through 12-M in the embodiments of Figures 7 and 9 are configured based on a
15 fixed or predetermined effective sampling rate (fs) of the DAC 26 using
the
process of Figure 5 in order to provide the concurrent multi-band signal (SmB)
with the desired carrier frequencies. In another embodiment, the effective
sampling rate (fs) of the DAC 26 is configured based on predetermined
parameters (e.g., complex tuning frequencies of the complex baseband tuners 18
20 and/or tuning frequencies of the image selection filters 22) in order to
provide the
concurrent multi-band signal (SmB) with the desired carrier frequencies.
[0081] Figure 11 illustrates the digital up-conversion system 10
according to
another embodiment of the present disclosure. In this embodiment, the digital
up-conversion system 10 is a variation of the embodiments of Figures 7 and 9
25 wherein the digital up-conversion system 10 further includes the
combined up-
converter 32 as discussed above with respect to Figure 6. The combined up-
converter 32 operates to provide additional up-conversion by a frequency
(fcomB)
subsequent to the combining of the complex up-converted digital signals
(lUP_1)
QUP_i through lup_m, QuP_m). In this example, the combined up-converter 32 is
30 subsequent to the digital quadrature modulator 34. However, the combined
up-
converter 32 may alternatively be prior to the digital quadrature modulator 34
and
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subsequent to the complex digital combiner 36. Note, however, that the
combined up-converter 32 is "real" if after digital quadrature modulation but
"complex" if before digital quadrature modulation.
[0082] The following acronyms are used throughout this disclosure.
= 3GPP 3rd Generation Partnership Project
= ASIC Application Specific Integrated
Circuit
= CDMA Code Division Multiple Access
= DAC Digital-to-Analog Converter
= FPGA Field Programmable Gate Array
= GHz Gigahertz
= MHz Megahertz
= RF Radio Frequency
[0083] Those skilled in the art will recognize improvements and
modifications
to the preferred embodiments of the present disclosure. All such improvements
and modifications are considered within the scope of the concepts disclosed
herein and the claims that follow.
