CA1249365A

CA1249365A - Process for recording and playback of tv-signals in analog form

Info

Publication number: CA1249365A
Application number: CA000447159A
Authority: CA
Inventors: Erich Geiger; Bernhard Otto
Original assignee: Deutsche Thomson Brandt GmbH
Current assignee: Deutsche Thomson Brandt GmbH
Priority date: 1983-02-11
Filing date: 1984-02-10
Publication date: 1989-01-24
Also published as: EP0118761B1; FI76662C; KR910004286B1; ATE27214T1; ES8501190A1; WO1984003190A1; DK487484D0; FI843973A0; EP0118761A1; JPS59189791A; DE3463717D1; FI843973L; AR241361A1; KR840008108A; DD230977A1; DE3304692C2; FI76662B; ES529659A0; DE3304692A1; DK487484A

Abstract

ABSTRACT

A method and apparatus for the transmission, recording, and playback of color television signals is provided. A luminance signal (Y) and a relative thereto narrow band chrominance signal (R-Y, B-Y) in each case are time-compressed and are transmitted successively during the line scanning period. The luminance signal togther with the horizontal synchonizing pulse and the front and back porch are time-compressed before the transmission. The signals are time expanded for reproduction such that they become time congruent for the picture reproduction. The simultaneous compression of luminance signal and line synchronizing pulses renders the method independent of the respective television standard, since the transmitted signal is changed back to the original signal.

Description

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 ~ L~3~

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 ~3~

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 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 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 3~

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 ~ ~3~9~

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 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 ____________________________________________________________ read and write of 2 of 3 Play 16 20 20 4 ~0 16 ___________~____________________________________ ______ read and write of 2 of 3 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, 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 $~

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 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 the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this inventionO

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for transmitting, recording and reproducing color television signals comprising time compressing the luminance signal (Y) together with the horizontal synchronizing pulse and the front and rear porch;
transmitting 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) in each case successively during the line scanning period in time compressed form;
time expanding the time-compressed luminance signal together with the horizontal synchronizing pulse and the front and back porch as well as the more narrow chrominance signal such that they become time congruent again for picture reproduction.

2. The method for transmitting, recording and reproducing color television signals according to claim 1 further comprising digitizing the luminance signal;
time-compressing the digitized luminance signal by writing it slowly into two alternating shift registers and by reading it more rapidly from the shift registers;
digitizing the chrominance signals (R-Y, B-Y);
time-compressing the chrominance signals by writing them alternating from line to line into a further shift register and reading them more rapidly;
converting the digitized signals into analog signals;
reproducing the signals coming from the shift registers after a corresponding time expansion.

3. The method for transmitting, recording and reproducing color television signals according to claim 2 further comprising generating a base cycle clock frequency with a single phase locked loop (PLL) circuit;
subdividing the base cycle clock frequency in frequency divider stages for generating the various clock pulses for controlling the digital-analog converter and the shift registers.

4. The method for transmitting, recording and reproducing color television signals according to claim 3 further comprising resetting the frequency dividers relative to the synchronizing pulses at defined times in order to obtain the edges 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.

5. The method for transmitting, recording and reproducing color television signals according to claim 2 further comprising double employing the digital circuit components for the time compression and for the time expansion.

6. The method for transmitting, recording and reproducing color television signals according to claim 2 further comprising feeding the time-compressed signal from a switching circuit to a digital-analog converter;
modulating the analog signal in a frequency modulator circuit;
amplifying the modulated analog signal; and recording the amplified signal.

7. The method for transmitting, recording and reproducing color television signals according to claim 6 further comprising reading the recorded signal;
amplifying the read signal in a reproduction amplifier;
feeding the amplified signal to a drop-out detector;
demodulating the signal coming from the drop-out detector;
converting the signal from the drop-out detector into a digital signal; and expanding the time-compressed digital signal.

8. The method for transmitting, recording and reproducing color television signals according to claim 2 wherein the luminance signal is by at least about 10 percent time-compressed.

9. An apparatus for transmitting, recording and reproducing color television signals comprising an N-MOS integrated circuit having a chrominance signal as input and including a timer and control circuit, shift registers connected to the timer and control circuit, and 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 having a luminance signal as input and including an analog-digital converter feeding its output to the shift registers;
a bipolar integrated circuit including a digital-analog converter connected to the output of the shift registers;
and a bipolar integrated circuit including 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.

10. An apparatus for transmitting, recording and reproducing color television signals comprising 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 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 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.

11. The apparatus for transmitting, recording and reproducing color television signals according to claim 10 further comprising a phase-locked loop (PLL) circuit having an input connected to the timer and control unit;
frequency dividers connected to the output of the phase locked loop and having outputs connected to the timer and control unit.

12. The apparatus for transmitting, recording and reproducing color television signals according to claim 10 further comprising an output switch connected to the third digital to analog converter;
a (FM) frequency-modulator connected to the output switch;
a recording amplifier connected to the frequency modulator;
and a recording device for the signal coming from the recording amplifier.

13. The apparatus for transmitting, recording and reproducing color television signals according to claim 10 further comprising a playback device;
a playback amplifier connected to the playback device;
a drop-out detector connected to the playback amplifier and having an output connected to the timer and control unit;
a (FM) frequency demodulator connected to the drop-out detector and to the luminance signal input switch.