Note: Descriptions are shown in the official language in which they were submitted.
2. Brief Description Q~ ~h~ Background Q~ ~h~
Invention Includina Prio~ ~L~
Methods of the kind set fort~above have been
described for example in German Patent DE-PS 2,056,684.
Later a series color coding method for home video recorders
was described in the journal "Fernseh- und Kinotechnik
(Television and Motion Picture Technique)"r Volume 34, Issue
12/80, pages 451 to 458 under the title: nTimeplex - a
series color coding method for home videorecorders(In
German)~. The reference teaches to time-compress the
chrominance signals for B-Y and R-Y into the blanking signal
by a factor of 5 and to record the time-compressed signals
between the synchronizing pulse and the luminance signalO
The Timeplex method continues to gain more and
more in importance since the recording of video signals is
performed with smaller and smaller tape speeds and with
narrower widths of the recording medium. The usually
longitudinal sound track is not any longer possible with 8
millimeter magnetic tapes based on the low magnetic tape
width and based on the low tape speed. Therefore, the sound
was recorded on a separate carrier and placed into the track
of the video signal. However, this results in negative cross
influences of the sound carrier on the various carrier
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frequencies of the picture signals and cross-color
disturbances result. The presently known Timeplex methods
have been realized by way of analog circuits for obtaining
chrominance, luminance and synchronizing signals. These
circuits are associated with the disadvantage that they
require a time delay line, that phase variations result and
that an offset of the luminance signal can result in case
the separately recorded synchronizing pulses have a bad
signal to noise ratio. In fact, these problems can be
resolved with more or less elaborate analog circiuctry,
however it was found that this expenditure can only be
reduced if the analog device components are replaced by
digital components and if a digital processing is performed.
This means that also the processing of the luminance signal
and of the synchronizing signal has to be digitalized.
Such methods with sequential transmission of time-
compressed signals require a relatively high expense for the
circuits. In addition, time shifts between the individual
signals can occur during reproduction, for example between
the line synchronizing pulse and the luminance signal.
S~M~ARY OF T~ INVENTION
1. Purpose~ of the Invention
It is an object of the present invention to
provide a method for time-multiplexing of television
signals.
It is another object of the present invention to
provide a method for color television transmission, where
time shifts between the individual signal parts are
substantially avoided after the transmission.
It is a further object of the present invention to
provide a digitizing method for the multiplexing step in
the transmission of color television signals.
These and other objects and advantages of the
present invention will become evident from the description
which follows.
2. Brief Descrietion ~ ~h~ Invention
The present invention provides according to one
aspect a method for transmitting, recording, playback and
reproducing color television signals. The luminance signal
(Y) together with the horizontal synchronizing pulse and the
front and back porch are time compressed. The time-
compressed luminance signal ~Y) together with the
hortizontal synchronizing pulse and the front and back porch
as well as a comparatively more narrow band chrominance
signal (R-Y, B-Y) are transmitted in each case successively
during the line scanning period in time compressed form. The
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time-compressed luminance signal together with the
horizontal synchronizing pulse and the front and back porch
as well as the more narrow chrominance signal are time
expanded such that they become time congruent again for
picture reproduction.
The luminance signal can be digitized. The
digitized luminance signal can be time-compressed by writing
it slowly into two alternating shift registers and by
reading it more rapidly from the shift registers~ The
chrominance signals (R-Y, B-Y) can be digitized. The
chrominance signals can be time-compressed by writing them
alternating from line to line into a further shift register
and by reading them more rapidly. The digitized signals can
be converted into analog signals. The signals coming from
the shift registers can be reproduced after a corresponding
time expansion.
A base cycle clock frequency can be generated with
a single phase locked loop (PLL) circuit. The base cycle
clock frequency can be subdivided in frequency divider
stages for generating the various clock pulses for
controlling the digital-analog converter and the shift
registers. The frequency dividers can be reset relative to
the synchronizing pulses at defined times in order to obtain
3~
the edqes of the clock pulses occurring simultaneously in
case of even multiples of the starting frequency of the
divider stages and to obtain the same write in and read out
points in time upon converting and reconverting of the time-
compressed signals. The digital circuit components can be
twice employed for the time compression and for the time
expansion.
The time-compressed signal can be fed from a
switching circuit to a digital-analog converter. The analog
signal can be modulated in a frequency modulator circuit.
The modulated analog signal can be amplified and the
amplified signal can be recorded. The recorded signal can be
read. The read signal can be amplified in a reproduction
amplifier. The amplified signal can be fed to a drop-out
detector. The signal coming from the drop-out detector can
be demodulated. The signal from the drop-out detector can be
converted into a digital signal. The time-compressed digital
signal can be expanded. The luminance signal can be time-
compressed by at last about 10 percent.
According to another aspect of the invention
there is provided an apparatus for transmitting, recording
and reproducing color television signals which comprises an
N-MOS integrated circuit including a timer and control
circuit, shift registers connected to the timer and control
circuit, an analog-digital converter connected to the timer
and control circuit, and digital-analog converters connected
to the output of the shift registers. A bipolar integrated
circuit includes an analog-digital converter feeding its
output to the shift registers. Also, a bipolar integrated
circuit includes a digital-analog converter connected to the
output of the shift registers. Further, a bipolar integrated
circuit includes a phase-locked loop (PLL) circuit, and
frequency dividers connected to the phase locked loop
circuit and to the shift registers and to the timer and
control unit.
According to a further aspect of the present
invention, an apparatus for transmitting, recording and
reproducing color television signals is provided which
comprises a luminance signal input switch for receiving
luminance signals, an analog to digital converter connected
to the output of the luminance switch, two parallel shift
registers connected to the output of the an analog to
digital converter, a signal output switch connected to the
outputs of the two parallel shift registers, a timer and
control unit connected to the output of the analog to
digital converter and having outputs connected to the two
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shift registers, and to the first analog to digital
converter, a switch to receive chrominance (R-Y, B-Y) signal
input, a second analog-digital converter connected to the
switch for chrominance input and to the timer and control
unit, an electronic switch connected to the output of the
first analog to digital converter and to the output of the
second analog to digital converter, a third shift register
connected to the output of the electronic switch and to the
output of the timer and control unit, a fourth shift
register connected to the output of the third shift register
and to the timer and control unit, an intermediate switch
connected to the output of the third shift register and to
the output of the fourth shift register, two digital to
analog converters connected to the intermediate switch and
having an output for the chrominance signals (R-Y, B-Y), a
switching stage connected to the timer and control unit, to
the output of the two shift registers and to the output of
the third shift register, and a third digital to analog
converter connected to the output of the switching stage and
to the timer and control unit and having a signal output.
A phase-locked loop (PLL) circuit can have an
input connected to the timer and control unit. Frequency
dividers can be connected to the output of the phase locked
loop and can have outputs connected to the timer and control
unit. An output switch can be connected to the third digital
to analog converter. A (FM) frequency-modulator can be
connected to the output switch. A recording amplifier can be
connected to the frequency modulator. A recording device can
be provided for the signal coming from the recording
amplifier. A playback amplifier can be connected to a
playback device. A drop-out detector can be connected to the
playback amplifier and can have an output connected to the
timer and control unit. A (FM) fequency demodulator can be
connected to the drop-out detector and to the luminance
signal input switch.
The circuit expense is kept low by time-
compressing and where necessary also time-expanding the
luminance signal together with the line synchronizing pulses
and the front and back porches in the same circuit, since
for the processiny of these signal parts only one circuit is
required. Since the signal parts are not being separated in
their processing, time shifts between these signals are
being avoided. If the combined signal of luminance signal,
line synchronizing pulse and front and back porch suffers a
time shift, then the time coordination between the line
synchronizing pulses and the luminance signal, which is
g
important for a flawless reproduction~ is advantageously
retained. Since the time-compression of the luminance signal
amounts to only about 20 percent, that is the luminance
signal is compressed to about ~0 percent of its original
time duration, there remains a sufficiently wide line
synchronizing pulse such that the deflection is not
interfered with during reproduction. The black level and the
synchronizing level are recovered practically as originally
existing. The half line frequency identification for the
sequentially transmitted chrominance signals can be
generated together with the achromatic level. In addition, a
drop-out compensation can be achieved by way of a memory
storage control. The outside number of connections can be
kept low by employing as far as possible integration of the
components necessary for the performance of the method. A
further advantage comprises that the method operates
independent of the television standard employed in each case
based on the simultaneous compression of luminance signal
and line synchronizing pulses, since the original of the
signal transmitted is recovered back.
The novel features which are considered as
characteristic for the invention are set forth in the
appended claims. The invention itself, however, both as to
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33~
its construction and its method of operation, together with
additional objects and advantages thereof, will be best
understood from the following description of specific
embodiments when read in connection with the accompanying
drawing.
BRIEF DESCRIPTION OF T~E DRAWING
In the accompanying drawing, in which are shown
several of the various possible embodiments of the present
invention:
Fig. 1 is a view of a schematic circuit diagram
illustrating the operation of the invention method,
Fig. 2 is a view of a diagram showing the time
dependence of the curve of the analog and digital signals.
DESCRIPTION OF INVENTION AND PREFERRED EMBODIHENTS
In accordance with the present invention there is
provided a method for the transmission and in particular
for the recording and playback of color television signals,
where a luminance signal (Y) and a comparatively narrower
chrominance signal (R-Y, B-Y) are transmitted in time-
compressed form and successive in time during the line
scanning period and the luminance signal (Y) and a
comparatively narrower chrominance signal (R-Y, B-Y) are
time expanded during reproduction such that they are
~3 1 à~ 3 3 ~ 5~
again congruent i.n time for the picture reproduction. The
improvement comprises that the luminance signal (Y) together
with the horizontal synchronizing pulse and the front and
back porch are time-compressed.
The luminance signal can be compressed such that
after digitizing the luminance signal is written slowly and
~0
alternatingly'two shift registers 2, 3 and read more rapidly
from the two shift registers 2, 3. The chrominance signals
(R-Y, B-Y) are time compressed in the way that after
digitization they are written to a further shift register 12
and they are read out more rapidly and the signals are then
again transformed into analog signals, where the signals are
correspondingly time expanded again employing the said
shift registers 2, 3, 12 for reproduction.
A single phase-locked loop (PLL) circuit 24 can
be provided generating a base clock frequency for obtaining
the various clock pulses for the control of the digital-
analog converter and the shift registers based on the
frequency divider stages 6, 7, 8. The frequency dividers 6,
7, 8 can be reset relative to the synchronizing pulses at
defined points in time for obtaining the edges of the clock
pulses occurring at about the same time relative to each
other in case of even multiples of the starting frequency of
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the divider stages and thereby the same write points and
read points in time are obtained upon changing and
rechanging of the time-compressed signals. The digital
component devices can be employed in a dual manner both for
the time-compression as well as for the time-expansion.
The circuit for advantageously performing the
time-compression and time expansion of the color television
signals can comprise a timer and control circuit 5 as well
as shift registers 2, 3, 12, 21 and the digital-analog
converter 10 as well as the digital-analog converters 22, 23
disposed on a N-MOS integrated circuit. The analog - digital
converter 1, the digital-analog converter 13 and the phase-
locked loop circuit 24 with the frequency dividers 6, 7, 8
can be disposed each on a bipolar integrated circuit.
The invention method cannot only be advantageously
employed for the recording and playback but can be employed
generally for the transmission of color television signals,
for example with satellite radio transmissions according to
the so-called C-Mac system, where also a sequential
transmission with time-compression is performed. The method
can also be employed in the transmission of color television
signals via cable or other transmission channels, in
particular of such channels which have a limited band width
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and which effect signal distortions such as for example time
shifts of the signal parts relative to each other.
Initially the recording of a color video signal on
a magnetic tape is to be described. For this purpose the
luminance signal Y is applied at the input of the analog-
digital converter 1 via the contact R. The analog-digital
converter 1 delivers a 7-bit wide parallel output signal
from the analog luminance signal and the output signal is
simultaneously fed to the memory storage 2 and 3 acting as
shift registers. These shift registers are written and read
alternatingly as controlled by the clock cycle. For example,
while the shift register 2 is written to, the information
contained in the shift register 3 is read and is applied to
the input of a switch 4. The time compression is achieved by
writing with a clock cycle of 16 megahertz and by reading
with a clock cycle of 20 megahertz. This means that the
luminance signal is compressed by about 20 percent such that
it occupies only about 80 percent of its original time
period. Such compression is preferably provided by an amount
of at least about 10 percent of the original time period.
The control unit 5 provides the clock and control pulses for
the digital-analog and analog-digital converters and for the
shift registers. The clock frequencies are picked up from a
generator operating according to the phase-locked loop (PLL~
technique. The base frequency of 80 megahertz obtained from
a single generator for the control or the complete circuit
is subdivided with the aid of the frequency divider stages
6, 7, 8 such that the system clock cycles of 20, 16 and 4
megahertz are generated. The chrominance signals R-Y and B-Y
are alternatingly applied to a switch 9 actuated with half
the line frequency H/2, which transforms the signal into a
6-bit information. This signal passes to the input P2 of an
electronic switch 11, at the output of which an electronic
shift register 12 is connected, which is controlled with a
clock cycle cl 3 delivered by the control unit 5~ This clock
cycle has a frequency of 4 megahertz for writing. The
reading is done at a frequency of 20 megahertz. The
information taken from the shift register 12 is applied to
the switching stage 4, which generates a digital 7-bit
signal depending on a control signal K from the control unit
5. The digital signal is composed of the luminance signal,
the chrominance signal and a fixed level. The digital signal
then passes via a digital-analog converter 13 and via the
contact R to a (FM) frequency modulation modulator 14 and is
fed to the recording apparatus 16 via the recording
amplifier 15.
Such a recorded signal is fed via a playback
amplifier 17, a drop-out detector 18 and via a (FM)
frequency modulation demodulator 1~ via the contact P to the
input of the digital-analog converter 1. Now the original
signal is recovered in reverse sequence from the time-
compressed signal. Again the two shift registers 2 and 3 are
alternatively written to and read out. The read signals are
applied to the input of the switch 4, which in this case
remains in the position for switching through of the
luminance signal. After a digital-analog conversion in the
converter 13 the luminance signal reaches the output via the
contact P for further processing in the connected
reproduction apparatus. The synchronizing signal Sy passes
to the control unit 5 and is there prepared. The time-
compressed chrominance signals pass via the input Pl of the
electronic switch 11 at its output 01 and from there to the
input of the shift register 12, the output of which is
applied directly to the input P3 of an electronic
intermediate switch 20 switchable at half the line frequency
H/2. In addition, the output of the shift register 12 is
applied to the input of a further shift register 21, the
output of which is led to a second input P4 of the
intermediate switch 20. Based on the alternating application
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of R-Y and ~-Y or, respectively, B-Y and R-Y signals at the
inputs P3 and P4 and the synchronous switching of the
intermediate switch 20 the R-Y 6-bit signal is generated at
it output 02 and the B-Y 6-bit signal is generated at its
output 03, which signals are available as R-Y and s-Y
chrominance signals after a transformation in the digital-
analog converters 22 and 23. An averaging of the color
information with the previous like color information is
produced based on these steps.
Advantageously, the drop-out compensation can be
performed digitally such that a digital control signal
obtained from the drop-out detector 18 activates the control
unit S via a line 26. Thereupon the shift registers 2 and 3
are loaded again for the luminance signal as well as shift
registers 12 and 21 for the chrominance signals with the
previous information.
The complete system is controlled by clock
frequencies, which are derived from a divided frequency
generated from a frequency, which is obtained from a single
phase-locked loop (PLL) circuit 24.
The following table presents the various clock
frequencies in megahertz as emp]oyed in the various mode~ of
operation
~2~
Clock 1 Clock 2 Clock 3 Clock 4 Clock 5
write read
read and write
of 2 of 3
Rec 20 16 4 20 16 20
________ ____________._________ ______._______ __________
read and write
of 2 of 3
16 20 4 20 16 20
____________________________________________________________
read and write
of 2 of 3
Play 16 20 20 4 ~0 16
___________~____________________________________ ______
read and write
of 2 of 3
16 20 4 20 16
The various analog and digital signals are
represented in Fig. 2.
Fig. 2a shows the analog luminance signal Y,
Fig. 2b shows the analog color signals R-Y and B-Y,
Fig. 2c shows the control clock cycle A for
writing into the shift register 2,
Fig. 2d shows the control clock cycle B for
writing to the shift register 3,
Fig. 2e shows the control clock cycle C for
writing to the shift register 2,
Fig. 2f shows the control clock cycle D for
reading of the shift register 2,
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Fig. 2g shows the control clock cycle E for
reading of the shift register 3,
Fig. 2h shows the control clock cycle F for
reading of the shift register 12,
Fig. 2i shows the achromacity level G, which is
added during the blanking interval from a circuit 25 to the
signal to be recorded,
Fig. 2k shows the control voltage K for the switch
4,
Fig. 21 shows the generated recording signal
(Timeplex signal).
The signals 2a to 21 correspond to the playback
and have the following frequencies in megahertz:
A B C D E F G
16 16 4 20 20 20 20 Mhz
The following signals correspond to the playback:
Fig. 2m shows the control clock cycle A for
writing to the shift register 2,
Fig. 2n shows the control clock cycle B for
writing to the shift register 3,
Fig. 2O shows the control clock cycle C for
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writing to the shift register 12,
Fig. 2p shows the the control clock cycle D for
reading of the shift register 2,
Fig~ 2q shows the control clock cycle E for
reading of the shift register 3,
Fig. 2r shows the control clock cycle F for
reading of the shift register 12 and for writing to the
shift register 21,
Fig. 2s shows the decompressed luminance signal Y,
Fig. 2t shows the decompressed chrominance signals
B-Y and R-Y.
The frequencies of the control clock cycles A to F
have the following values in megahertz:
A B C D E F
16 16 4 Mhz
A circuit for performing the method of the present
invention is particularly desirable as an integrated
circuit. In order to render the circuit flexible and
economic the component devices can be subdivided into
several groups, where the timer and control circuit 5 as
well as the shift registers 2, 3, 12 and 21 as well as the
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analog to digital converter 10 and the digital to analog
converter 22 and 23 are disposed on a N-MOS-IC and where the
the analog-digital converter 1 together with the digital-
analog converter 13 and the phase-locked loop (PLL) 24 with
the frequency dividers 6, 7, 8 are each disposed on a
bipolar integrated circuit IC.
It will be understood that each of the elements
described above, or two or more together, may also find a
useful application in other types of high frequency
transmission system configurations and color television
signal processing procedures differing from the types
described above.
While the invention has been illustrated and
described as embodied in the context of a system for
transmission of color television signals, it is not intended
to be limited to the details shown, since various
modifications and structural changes may be made without
departing in any way from the spirit of the present
invention.
Without further analysis, the foregoing will so
fully reveal the gist of the present invention that others
rcan, by applying current knowledge, readily adapt it for
various applications without omitting features that, from
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the standpoint of prior art, fairly constitute essential
characteristics of the generic or specific aspects of this
inventionO
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