Canadian Patents Database / Patent 2323023 Summary

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(12) Patent Application: (11) CA 2323023
(54) English Title: DOUBLE BALANCED MIXER
(54) French Title: MELANGEUR DOUBLEMENT SYMETRIQUE
(51) International Patent Classification (IPC):
  • H03F 3/68 (2006.01)
  • H03D 7/14 (2006.01)
  • H03F 3/45 (2006.01)
  • H04B 1/26 (2006.01)
  • H04S 7/00 (2006.01)
(72) Inventors :
  • AMACHI, NOBUMITSU (Japan)
  • FUJIWARA, HIROKI (Japan)
  • HIGASHIKAWA, YOSHIKUNI (Japan)
(73) Owners :
  • MURATA MANUFACTURING CO., LTD. (Japan)
(71) Applicants :
  • MURATA MANUFACTURING CO., LTD. (Japan)
(74) Agent: SIM & MCBURNEY
(74) Associate agent:
(45) Issued:
(22) Filed Date: 2000-10-06
(41) Open to Public Inspection: 2001-04-07
Examination requested: 2000-10-06
(30) Availability of licence: N/A
(30) Language of filing: English

(30) Application Priority Data:
Application No. Country/Territory Date
11-286651 Japan 1999-10-07

English Abstract




A double-balanced mixer includes a first pair of
differential amplifiers, in which first electrodes of the
first and second transistors are connected to a current
source, and a first input signal is applied to second
electrodes of the first and second transistors, a second
pair of differential amplifiers, in which the first
electrodes of the third and fourth transistors are connected
to a third electrode of the first transistor, and a second
input signal is applied to the second electrode of the third
and fourth transistors, a third pair of differential
amplifiers, in which the first electrodes of the fifth and
sixth transistors are connected to the third electrode of
the second transistor, and the second input signal is
applied to the second electrodes of the fifth and sixth
transistors, and an impedance element provided between the
first electrodes of the first and second transistors. In
the double-balanced mixer, the third electrodes of the third
and fifth transistors are connected, the third electrodes of
the fourth and sixth transistors are connected, the current
source includes a first current source and a second current
source in which substantially identical currents flow, and
the first electrode of the first transistor and the first
electrode of the second transistor are connected to the



-19-

first and second current sources, respectively.


Note: Claims are shown in the official language in which they were submitted.



-16-



WHAT IS CLAIMED IS:



1. A double-balanced mixer comprising:
a first pair of differential amplifiers including a
first and second transistors, source or emitter of the first
transistor being connected to a first current source, source
or emitter of the second transistor being connected to a
second current source, a first input signal being inputted
to gate or base of the first and second transistors,
substantially the same value of currents is applied into the
first and second current sources, and an impedance element
being connected between the source or emitter of the first
transistor and the source or emitter of the second
transistor;
a second pair of differential amplifiers including a
third and fourth transistors, each source or emitter of the
third and fourth transistors being connected to drain or
collector of the first transistor, and a second input signal
being inputted to each gate or base of the third and fourth
transistors;
a third pair of differential amplifiers including a
fifth and sixth transistors, each source or emitter of the
fifth and sixth transistors being connected to drain or
collector of the second transistor, and the second input
signal being inputted to each gate or base of the fifth and



-17-



sixth transistors;
wherein drain or collector of the third transistor is
connected to drain or collector of the fifth transistor,
drain or collector of the fourth transistor is connected to
drain or collector of the sixth transistor, and a mixed
signal obtained by mixing the first input signal and the
second input signal is outputted between the drain or
collector of the third transistor and the drain or collector
of the sixth transistor.
2. A double-balanced mixer according to Claim 1,
wherein said impedance element comprises an inductor.
3. A double-balanced mixer according to one of Claims
1 and 2, wherein each of the first and second current
sources comprises a transistor.
4. A double-balanced mixer according to Claim 3,
wherein each source or emitter of the two transistors
constituting the first and second current sources is
commonly connected, and the two transistors are provided in
adjacent regions on a semiconductor integrated circuit.

Note: Descriptions are shown in the official language in which they were submitted.


f
CA 02323023 2000-12-19
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DOUBLE-BALANCED MIXER
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a double-balanced
mixer using transistors.
2. Description of the Related Art
Fig. 6 shows a block diagram of a double-balanced mixer.
Differential amplifiers AMP respectively amplify a local
signal Lo and a radio frequency signal RF and output the
amplified signals to a mixer MIX. The mixer MIX outputs an
intermediate frequency signal IF.
As the mixer MIX, a so-called Gilbert cell mixer is
used and is conventionally constructed as shown in Fig. 7.
A constant current source is provided for supplying a
constant current and a power supply V~~ is provided for
biasing the transistors.
An oscillation-preventing resistors Re serves to improve
the linearity of the mixer MIX. However, as the resistance
of the resistor Re becomes higher, the conversion voltage
gain drops. In order to avoid such a drop in the conversion
voltage gain regardless of the increase in the resistance of
Re, the resistances of output loads 3 and 4, or the current
of the constant current source may be increased. However,
increasing those values leads to a decrease in the


CA 02323023 2000-12-19
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saturation level of the circuit. Furthermore, in order to
increase the current of the constant current source, the
resistances of the resistors Re must be reduced to a very
small level. When the resistances are reduced to a very
small level, since the offset of the voltage drop across the
resistor Re caused by slight variations of the resistance of
the resistor Re becomes relatively great, the output balance
of the mixer MIX is worsened.
To solve such a typical problem of the,double-balanced
mixer using transistors, as disclosed in Japanese Unexamined
Utility Model Application Publication No. 5-59938 or U.S.
Pat. No. 5,625,307, instead of the resistors Re shown in Fig.
7, an inductor is provided between the emitters of
transistors Q1 and Q2 and the constant current source.
By providing the inductor between the constant current
source and the emitters of the two transistors which are
differentially connected, since the direct current bias and
the alternating current can be set separately, the linearity
of the input/output characteristics as well as the
conversion voltage gain can be improved.
When the above-described double-balanced mixer is
applied to a microwave integrated circuit, since the
inductor is obtained by forming the wiring pattern thereof
into, for example, a spiral shape, the area occupied by the
inductor on the integrated circuit becomes great: When two


CA 02323023 2000-12-19
- 3 -
inductors are provided in the integrated circuit, sufficient
space is required between the two inductors so that
electromagnetic coupling does not occur therebetween. This
leads to a further increase in the area occupied by the
inductors. In construction of the microwave integrated
circuit, the number of components on a wafer has a
considerable influence on the cost of the integrated circuit.
Hence, the greater the chip area, the higher the cost.
When the current of the constant current source is
increased in order to increase the conversion voltage gain,
the wiring width of the inductor must be increased so that
the current rating of the constant current source is
satisfied. As a result, the area occupied by the inductor
is further increased.
Since a direct current flows through the inductor,
migration may cause a short circuit within the spiral
inductor or between the two inductors. In the case of the
occurrence of the short circuit, the inductance of the
inductor becomes less than the design inductance, which
leads to variations in the electrical characteristics.
SUMMARY OF THE INVENTION '
Accordingly, it is an object of the present invention
to provide a miniaturized, less expensive, and highly
reliable double-balanced mixing circuit having stable

CA 02323023 2000-12-19
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characteristics by solving the foregoing problems.
To this end, there is provided a double-balanced mixer
comprising: a first pair of differential amplifiers
including a first and second transistors, source or emitter
of the first transistor being connected to a first current
source, source or emitter of the second transistor being
connected to a second current source, a first input signal
being inputted to gate or base of the first and second
transistors, substantially the same value of currents is
applied into the first and second current sources, and. an
impedance element being connected between the source or
emitter of the first transistor and the source or emitter of
the second transistor; a second pair of differential
amplifiers including a third and fourth transistors, each
source or emitter of the third and fourth transistors being
connected to drain or collector of the first transistor, and
a second input signal being inputted to each gate or base of
the third and fourth transistors; a third pair of
differential amplifiers including a fifth and sixth
transistors, each source or emitter of the fifth and sixth
transistors being connected to drain or collector of the
second transistor, and the second input signal being
inputted to each gate or base of the fifth and sixth
transistors; wherein drain or collector of the third
transistor is connected to drain or collector of the fifth


CA 02323023 2000-12-19
- 5 -
transistor, drain or collector of the fourth transistor is
connected to drain or collector of the sixth transistor, and
a mixed signal obtained by mixing the first input signal and
the second input signal is outputted between the drain or
collector of the third transistor and the drain or collector
of the sixth transistor.
Since this construction allows a single impedance
element to be used, the occupied area thereof is decreased.
By causing values of the currents flowing in the first
and second current sources to be substantially equal, since
the direct current component which flows via the impedance
element can be decreased, the wiring width of the impedance
element can be greatly reduced. Accordingly, the area
occupied by the impedance element is further reduced.
In addition, since the direct current through the
impedance element can be decreased, migration can be
prevented. Accordingly, reliability of the double-balanced
mixer can be improved and electrical characteristics thereof
can be stabilized.
Since the direct current through the impedance element
can be decreased, a direct current bias (paths of the direct
current) and an alternating current signal (paths of the RF
signal) can be separately set. Therefore, since voltage
feedback is applied in series to the input terminals of the
radio frequency signal RF by the voltage generated between


CA 02323023 2000-12-19
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both ends of the impedance element, linearity of
input/output characteristics can be improved. Accordingly,
oscillation of the double-balanced mixer can be prevented.
In the double-balanced mixer, the impedance element
comprises an inductor. Since the phase of the voltage-
feedback applied in series across the input terminals of the
radio frequency signal RF can be shifted by 90° (ninety
degrees), the conversion voltage gain can be increased.
While the conversion gain is improved in the frequency
band of the radio frequency signal RF, the conversion gain
in the frequency band of image signal is decreased. Noise
components which is converted from the image signal can be
reduced without decreasing the conversion gain of the high
frequency signals (radio frequency signal). Accordingly,
the noise factor of the double-balanced mixer can be
improved.
In the double-balanced mixer, each of the first and
second current sources includes a transistor. Since the
currents flowing from each of the first current source and
the second current source is half the value of the current
flowing from the single current source of the conventional
mixer, when the first current source and the second current
source are constructed using transistors, the area occupied
by each current source can be halved and the circuit
configuration is made without increasing the entire occupied


CA 02323023 2000-12-19
-
area.
In the double-balanced mixer, each source or emitter of
the two transistors constituting the first and second
current sources is commonly connected, and the two
transistors are provided in adjacent regions on a
semiconductor integrated circuit.
Since this construction enables the wiring efficiency
of the first current source and the second current source to
be increased, the area occupied by the current sources can
be further decreased. Furthermore, electrical
characteristics of the two current sources can be made
uniform. Regardless of changes in temperature or voltage
fluctuations of the power supply, since a direct current
never flows through the impedance element, the wiring width
of the impedance element can be considerably decreased.
Accordingly, the risk of encountering migration is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram showing the construction of
a double-balanced mixer according to a first embodiment of
the present invention;
Fig. 2 is a detailed circuit diagram showing the
construction of an impedance element and the construction of
constant current sources in the mixer shown in Fig. 1;
Fig. 3 is a graph illustrating the relationship between


CA 02323023 2000-12-19
- $ -
the frequency and the conversion gain of the double-balanced
mixer shown in Fig. 2;
Fig. 4 is a detailed circuit diagram showing the
construction of transistors Q7 and Q8 in the mixer shown in
Fig. 2;
Fig. 5 is a circuit diagram showing the construction of
a double-balanced mixer according to a second embodiment of
the present invention;
Fig. 6 is a block diagram of the double-balanced mixer;
and
Fig. 7 is a circuit diagram showing the construction of
a conventional double-balanced mixer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows the configuration of a double-balanced
mixer according to a first embodiment of the present
invention.
First and second transistors Q1 and QZ constitute a
first pair of differential amplifiers so that the sources of
the first and second transistors Q1 and Q2 are connected to
constant current sources 1 and 2, respectively. Third and
fourth transistors Q3 and Q4 constitute a second pair of
differential amplifiers so that the sources of the third and
fourth transistors Q3 and Q4 are connected to the drain of
the first transistor Q1 and so that a local signal Lo is


CA 02323023 2000-12-19
_ g _
input to the gates of the transistors Q3 and Q4. Fifth and
sixth transistors QS and Q6 constitute a third pair of
differential amplifiers so that the sources of the fifth and
sixth transistors QS and Q6 are connected to the drain of the
second transistor QZ and so that the local signal Lo is
input to the gates of the transistors Q5 and Q6. The drains
of the transistors Q3 and QS are connected and the drains of
the transistors Q4 and Q6 are connected. An output load 3 is
provided between a power source VDD and the connection point
of the drains of the transistors.Q3 and Q5, and an output
load 4 is provided between the power source vDp and the
connection point of the drains of the transistors Q4 and Q6.
An intermediate frequency signal IF is output between the
drains of the transistors Q3 and Q6 or between the drains of
the transistors Q4 and Q5.
In the double-balanced mixer, the current values of the
constant current sources 1 and 2 are substantially equal and
the impedance values of the output loads 3 and 4 are also
substantially equal. The current values of the constant
current sources 1 and 2, and the impedance values of the
output loads 3 and 4 are determined such that a conversion
voltage gain can be obtained in accordance with a desired
output level in addition to the linearity of the
input/output characteristics is ensured by an impedance
circuit 5.


CA 02323023 2000-12-19
- 10 -
The local signal Lo having a level in which a limiter
is activated to normal local signal level, in other words,
having a level of the signal greater than that of the signal
which allows square waves to be output, is inputted. The
radio frequency signal RF having a level which does not
cause the limiter to be activated is inputted. Therefore,
in the second pair of differential amplifiers including the
transistors Q3 and Q4 and the third pair of differential
amplifiers including the transistors Q5 and Q6, the local
signal Lo causes the transistor pair Q3 and Q5 and the
transistor pair QQ and Q6 to function as a synchronous switch.
In accordance with switching operations of the synchronous
switches, the radio frequency signal RF, or high frequency
signal, and the local signal Lo are mixed and the mixed
signal is output as the intermediate frequency signal IF.
At this time, feedback voltage is applied in series to the
input terminals of the radio frequency signal RF by the
voltage generated at both ends of the impedance element 5.
Because of this, since the linearity of the input/output
characteristics of the mixer is improved, oscillation
thereof is prevented.
Fig. 2 shows a more detailed configuration of the
double-balanced mixer. In Fig. 2, an inductor L constitutes
the impedance element 5 shown in Fig. 1 and transistors
and Q8 constitute a part of the constant current sources 1


CA 02323023 2000-12-19
- 11 -
and 2, respectively. With this configuration voltage-
feedback is applied in series to the input terminals of the
radio frequency signal RF by the inductor L. Here, the
voltage waveform is assumed to be a sine wave. Compared to
a case in which the impedance element 5 is a resistor having
an impedance which is equal to the impedance cuL of the
inductor L, phase of the voltage feedback is shifted by 90
degrees. Since the amplitude ratio of the synthesized
(product) waveform of two voltages whose phase difference is
90 degrees to the synthesized waveform of two voltages whose
phase difference is zero is (d2)/2, the equation is
expressed as 20 x log((~/2)/2) - -3 dB. Hence, the feedback
value is decreased by 3 dB. This means that the conversion
voltage gain is improved by 3 dB when the same linearity of
input/output characteristics is obtained as in the case in
which the feedback is applied using the resistor.
Fig. 3 shows the relationship between the frequency and
the conversion voltage gain of the double-balanced mixer-in
Fig. 2. For example, the frequency of the radio frequency
signal RF which is input to the gates of the transistors Ql
and Q2 is assumed to be in a range of 50 MHz to 1 GHz; the
frequency of the local signal Lo which is input to the gates
of the transistors Q3 to Q6 is assumed to be in the range of
1.55 GHz to 2.5 GHz; and the frequency of the intermediate
signal IF which is output from the drains of the transistors


CA 02323023 2000-12-19
- 12 -
Q3 to Q6 is assumed to be 1.5 GHz. At this time, an image
signal having a frequency of greater than 3 GHz is also
converted into the intermediate signal IF having a frequency
of 1.5 GHz by the local signal Lo having a frequency of 1.55
GHz to 2.5 GHz. Since this intermediate signal IF of the
image signal is regarded as a noise component, therefore it
is important to suppress the conversion voltage gain of the
frequency band, of the image signal.
According to Fig. 3, in comparison with the case in
which the resistor is used as the impedance element 5, it~is
understood that there are the following advantages in the
case in which the inductor is used as the impedance circuit
5: the conversion voltage gain is improved in the range of
50 MHz to 1 GHz which is the frequency band of the radio
frequency signal RF; and the conversion voltage gain is
suppressed in the range of greater than 3 GHz which is a
frequency band of the image signal. This is because,
compared to the resistor, the impedance of the inductor is
small in the frequency band of the radio frequency RF, that
is, loss of the inductor itself is small. Further, the
impedance of the inductor becomes large in the frequency
band of the image signal. Therefore, since the noise
component converted from the image signal can be reduced
without decreasing the conversion gain of the radio
_frequency signal RF, the noise factor of the double-balanced


CA 02323023 2000-12-19
- 13 -
mixer can be improved.
Fig. 4 shows more detailed configuration of the
transistors Q~ and Q8 which constitute a part of the constant
current sources 1 and 2, respectively. The transistors Q~
and Q8 are configured using depletion-type FETs (Field-
Effect Transistor). They are arranged in the same area on a
chip so that a gate connection G is shared therebetween and
the drains D1 and D2 and the sources S1 and SZ are symmetric.
The current flowing through each of the transistors Q~ and Q8
is half when compared with the case where the constant
current source to which a single transistor connected is
provided between a pair the differential amplifiers and the
ground in a conventional manner. That is, when Idss
(representing a drain current according to the gate-voltage
versus drain-current characteristics of the depletion-type
FET when the gate voltage is zero) of each of the FET
transistors Q~ and Qe is half of the Idss of the
corresponding transistor of the conventional mixer, it is
sufficient that the gate width of each of the transistors Q~
and Q8 is half of the gate width of the transistor of the
conventional mixer. This causes the area occupied by each
of the transistors to be halved. Accordingly, provision of
the two transistors Q~ and Q8 does not lead to an increase in
the overall size of the mixer. Furthermore, since the two
transistors Q~ and Q8 are provided in the same area on the


CA 02323023 2000-12-19
- 14 -
chip so as to be in contact with each other, the
characteristics of the constant current sources l and 2 can
remain uniform. Therefore, regardless of changes in
temperature or changes in the voltage of the power supply,
the direct current can be controlled so as not to flow
through the inductor L by balancing the direct current bias.
Fig. 5 shows the construction of another double-
balanced mixer. Unlike that shown in Fig. 1, the mixer is
constructed using bipolar transistors. Accordingly, the
local signal Lo and the radio frequency signal RF are
current-input type signals. Otherwise, the double-balanced
mixer in Fig. 5 functions in substantially the same manner
as that shown in Fig. 1. Furthermore, the constant current
sources 1 and 2 can be constructed using bipolar transistors.
In this case, by'providing bipolar transistors in the same
area of the chip, the area occupied by the transistors
should not be increased. In the same manner as in the
constant current source described in the foregoing
embodiment, the characteristics of the constant current
sources remain uniform.
In the foregoing, embodiments have been described in
which the two constant current sources are provided between
the ground and the sources or emitters of the first pair of
differential amplifiers. As long as the currents of these
two current sources are balanced, the currents may be varied


CA 02323023 2000-12-19
- 15 -
in accordance with changes in the power supply. This means
that the two current sources are not necessarily constant
current sources and mere current sources suffice for the
mixer.

A single figure which represents the drawing illustrating the invention.

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Admin Status

Title Date
Forecasted Issue Date Unavailable
(22) Filed 2000-10-06
Examination Requested 2000-10-06
(41) Open to Public Inspection 2001-04-07
Dead Application 2003-12-22

Abandonment History

Abandonment Date Reason Reinstatement Date
2002-12-23 R30(2) - Failure to Respond
2003-10-06 FAILURE TO PAY APPLICATION MAINTENANCE FEE

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $400.00 2000-10-06
Registration of a document - section 124 $100.00 2000-10-06
Application Fee $300.00 2000-10-06
Maintenance Fee - Application - New Act 2 2002-10-07 $100.00 2002-09-23
Current owners on record shown in alphabetical order.
Current Owners on Record
MURATA MANUFACTURING CO., LTD.
Past owners on record shown in alphabetical order.
Past Owners on Record
AMACHI, NOBUMITSU
FUJIWARA, HIROKI
HIGASHIKAWA, YOSHIKUNI
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Cover Page 2001-03-23 1 44
Representative Drawing 2001-03-23 1 6
Drawings 2000-10-06 5 67
Description 2000-12-19 15 515
Claims 2000-12-19 2 60
Abstract 2000-12-19 2 40
Drawings 2000-12-19 4 44
Abstract 2000-10-06 2 41
Description 2000-10-06 15 509
Claims 2000-10-06 2 60
Fees 2002-09-23 1 55
Assignment 2000-10-06 4 160
Prosecution-Amendment 2000-12-19 24 692
Prosecution-Amendment 2002-08-22 2 47