Color video signal synthesizer

Abstract

A video signal synthesizer operable to provide a multiplex video signal for producing a picture-in-picture effect on a display screen of a display device, for example, a cathode ray tube. The video signal synthesizer utilizes a PLL (phase-locked loop) circuit to generate a carrier signal synchronized with a color burst signal contained in the composite video signal for the reproduction of the main picture. The carrier signal is first delayed by a delay circuit and then utilized to remodulate the sub-picture signal which has been compressed with respect to time. This remodulated sub-picture signal is then subjected to time-division multiplexing through analog switch assembly. The delay time of the delay circuit is set so that both color subcarrier signals of the main picture and sub-picture signals may be matched in phase. Hence, the time-division multiplexing of the main picture signal and the sub-picture signal is possible without altering the characteristics of the color composite video signal. Thus, the necessity of the main picture signal being demodulated and modulated can be obviated.

What is claimed is: 
     
       1. A video signal synthesizer for producing a synthetic composite video signal which reproduces a main picture on a screen of a display device and a reduced sub-picture within the framework of and in a superimposed relationship with the main picture on the same screen by synthesizing a first composite video signal reproducing the main picture, a second composite video signal reproducing the sub-picture and a third composite video signal obtained by reducing said second composite video signal, comprising: phase-locked loop means for generating first and second carrier signals;   extracting means for extracting a color burst signal from the first composite video signal, wherein the color burst signal and the first composite video signal have a mutual phase difference of 90 degrees;   synchronizing means for synchronizing the color burst signal with the first and second carrier signals;   first and second delay means for delaying the first and second carrier signals by predetermined quantities respectively;   separating means for separating the second composite video signal into a luminance signal, a red color difference signal, and a blue color difference signal,   means for time-compressing the luminance signal, the red color difference signal, and the blue color difference signal;   reduced sub-picture signal producing means for producing the third composite signal from the time-compressed luminance signal, the red color difference signal, and the blue color difference signal, comprising,   chroma modulating means for chroma modulating the time-compressed red color difference signal and the time-compressed blue color difference signal by the delayed first and second carrier signals to obtain a color subcarrier signal, and   adding means for adding the time-compressed luminance signal to the color subcarrier signal to produce the third composite under signal, and   time-division multiplexing means for time-division multiplexing the first composite video signal and the third composite video signal to thereby deliver said synthetic composite video signal;   whereby the delay-time of the first and second delay means is set such that the color subcarrier signal of the first composite video signal and the color sub-carrier signal of third composite video signal may be matched in phase in accordance with the set delay time of the first and second delay means.   
     
     
       2. A video signal synthesizer as claimed in claim 1, which further comprises plural reduced sub-picture signal producing means for receiving the first and second carrier signals as carrier signals for chroma modulation, and wherein the time-division multiplexing means multiplexes plural third composite video signals and the first composite video signals delivered from the plural reduced sub-picture signal producing means. 
     
     
       3. A video signal synthesizer for producing a synthetic composite video signal which reproduces a main picture on a screen of a display device and a reduced sub-picture within the framework of and in a superimposed relationship with the main picture on the same screen by synthesizing a first composite video signal reproducing the main picture, a second composite video signal reproducing the sub-picture and a third composite video signal obtained by reducing said second composite video signal, comprising: phase-locked loop means for generating a first continuous wave signal;   extracting means for extracting a color burst signal from the first composite video signal;   synchronizing means for synchronizing the color burst signal with the first continuous wave signal;   separating means for separating the second composite video signal into a luminance signal, a red color difference signal, and a blue color difference signal,   means for time-compressing the luminance signal, the red color difference signal, and the blue color difference signal;   reduced sub-picture signal producing means for producing the third composite signal from the time-compressed luminance signal, the red color difference signal, and the blue color difference signal, comprising   chroma modulating means for chroma modulating the time-compressed red color difference signal and the time-compressed blue color difference signal by first and second carrier signals having a mutual phase difference of 90 degrees, and   adding means for adding the time-compressed luminance signal to a color subcarrier signal to produce the third composite video signal;   second phase-locked loop means for generating a second continuous wave signal synchronized with a color burst signal extracted from the color sub-carrier signal.   phase detector means for comparing the phase of the first and second continuous wave signals and delivering a phase difference signal corresponding to the phase difference thereof;   carrier signal generating means for generating first and second carrier signals have a mutual phase difference of 90 degrees being controlled by said phase difference signal and synchronized with the phase of said first continuous wave signal, wherein the chroma modulating means utilizes the first and second carrier signals generated in the carrier signal generating means as the first and second carrier signals for chroma modulation of the reduced sub-picture producing signal; and   time-division multiplexing means for time-division multiplexing the first composite video signal and the third composite video signal to thereby deliver said synthetic composite video signal.   
     
     
       4. A video signal synthesizer as claimed in claim 3, which further comprises plural reduced sub-picture signal producing means for receiving the first and second carrier signals as carrier signals for chroma modulation, and wherein the time-division multiplexing means multiplexes plural third composite video signals and the first composite video signals delivered from the plural reduced sub-picture signal producing means. 
     
     
       5. A video signal synthesizer as claimed in claim 3, which further comprises: sync signal generator means for generating a sync signal corresponding to the sync signal of the first composite video signal;   operating reference voltage source means for delivering an operating reference voltage of the carrier signal generating means consisting of a voltage-controlled oscillator;   control means responsive to the sync signal for delivering control signals to control the multiplexing means and the reduced sub-picture signal producing means in synchronism with the first composite video signal;   means for delivering a missing signal when an absence of the first composite video signal is detected;   first switching means for maintaining the control signals delivered from said control means by selectively feeding the sync signal of the first composite video signal or the sync signal delivered from the sync signal generator means to said control means, the latter sync signal being fed when the missing signal is received;   and second switching means for maintaining the generation of the first and second carrier signals by selectively feeding the phase difference signal delivered from the phase detector means or the operating reference voltage to the voltage-controlled oscillator, the operating reference voltage being fed when the missing signal is received.   
     
     
       6. A video signal synthesizer for producing a synthetic composite video signal which reproduces a main picture on a screen of a display device and a reduced sub-picture within the framework of and in a superimposed relationship with the main picture on the same screen by synthesizing a first composite video signal reproducing the main picture, a second composite video signal reproducing the sub-picture and a third composite video signal obtained by reducing said second composite video signal, comprising: a carrier signal generating means for generating first and second carrier signals having a mutual phase difference of 90 degrees,   synchronizing means for synchronizing the color burst signal with the first and second carrier signals;   first and second delay means for delaying the first and second carrier signals by predetermined quantities respectively;   separating means for separating the second composite video signal into a luminance signal, a red color difference signal, and the blue color difference signal;   means for time-compressing the luminance signal, the time-compressed red color difference signal and the time-compressed blue color difference signal by the delayed first and second carrier signals to obtain a color subcarrier signal;   adding means for the time-compressed luminance signal to the color subcarrier signal to produce the third composite video signal;   reduced sub-picture signal producing means for producing the third composite video signal from the time-compressed luminance signal, the red color difference signal, and the blue color difference signal wherein the chroma modulating means utilizes the first and second carrier signals generated in the carrier signal generating means as the delayed first and second carrier signals for chroma modulation of the reduced sub-picture producing signal;   first and second color burst signal extraction means for extracting color burst signals from the first composite video signal and the third composite video signal respectively;   phase detector means for comparing the phase of the color burst signal extracted from the first composite video signal by the first color burst signal extraction means with the phase of the color burst signal extracted from the third composite video signal by the second color burst signal extraction means, and delivering a phase difference signal corresponding to the phase difference thereof; said carrier signal generating means controlling the phase difference of said first and second carrier signals by utilizing the phase difference signal;   said synchronizing means synchronizing the phase of the first color burst signal with the phase difference; and   time-division multiplexing means for time-division multiplexing the first composite video signal and the third composite video signal to thereby deliver said synthetic composite video signal.   
     
     
       7. A video signal synthesizer as claimed in claim 6, which further comprises plural reduced sub-picture signal producing means for receiving the first and second carrier signals as carrier signals for chroma modulation, and wherein the time-division multiplexing means multiplexes plural third composite video signals and the first composite video signals delivered from the plural reduced sub-picture signal producing means. 
     
     
       8. A video signal synthesizer as claimed in claim 6, which further comprises: sync signal generator means for generating a sync signal corresponding to the sync signal of the first composite video signal;   operating reference voltage source means for delivering an operating reference voltage of the carrier signal generating means consisting of a voltage-controlled oscillator;   control means responsive to the sync signal for delivering control signals to control the multiplexing means and the reduced sub-picture signal producing means in synchronism with the first composite video signal;   means for delivering a missing signal when an absence of the first composite video signal is detected;   first switching means for maintaining the control signals delivered from said control means by selectively feeding the sync signal of the first composite video signal or the sync signal delivered from the sync signal generator means to said control means, the latter sync signal being fed when the missing signal is received;   and second switching means for maintaining the generation of the first and second carrier signals by selectively feeding the phase difference signal delivered from the phase detector means or the operating reference voltage to the voltage-controlled oscillator, the operating reference voltage being fed when the missing signal is received. .Iadd.   
     
     
       9.  A video signal synthesizer for producing a synthetic composite video signal which reproduces a main picture on a screen of a display device and a reduced sub-picture within the framework of and in a superimposed relationship with the main picture on the same screen by synthesizing a first composite video signal reproducing the main picture and a third composite video signal reproducing the sub-picture obtained by reducing a second composite video signal, comprising; synchronizing means for synchronizing a color subcarrier signal of the third composite video signal with a color subcarrier signal of the first composite video signal in phase;   separating means for separating the second composite video signal into a luminance signal, a red color difference signal, and a blue color difference signal;   means for time-compressing the luminance signal, the red color difference signal, and the blue color difference signal;   reduced sub-picture signal producing means for producing the third composite signal from the time-compressed luminance signal, the time-compressed red color difference signal and the time-compressed blue color difference signal, comprising,   chroma modulating means for chroma modulating the time-compressed red color difference signal and the time-compressed blue color difference signal to provide the color subcarrier signal of the third composite video signal, and   adding means for adding the time-compressed luminance signal to the color subcarrier signal to produce the third composite video signal; and   time-division multiplexing means for time-division multiplexing the first composite video signal and the third composite video signal to thereby deliver said synthetic composite video signal. .Iaddend. .Iadd.   
     
     
       10.  A picture-in-picture circuit comprising: a sub-picture demodulator demodulating a desired sub-picture signal to produce sub-picture component signals, said sub-picture component signals including separated luminance and chrominance sub-picture signal portions;   a memory for storing said luminance and chrominance sub-picture signal portions in first and second memory areas;   a synchronization signal generator for generating a first synchronization signal from a main picture signal;   a color synchronizer generating at least one color sub-picture synchronization signal synchronized to said main picture color subcarrier signal but delayed with respect thereto;   a reader reading the output of said memory under control of said synchronization signal to thereby develop a synchronized sub-picture signal synchronized to said main picture signal; and   a chrominance modulator for modulating said separated chrominance sub-picture portion to produce a sub-picture color subcarrier signal synchronized to said main picture color subcarrier signal under control of said at least one color sub-picture synchronization signal. .Iaddend. .Iadd.11. The picture-in-picture circuit of claim 10 wherein said sub-picture demodulator further demodulates said chrominance sub-picture portions into red and blue color difference signals. .Iaddend. .Iadd.12. The picture-in-picture circuit of claim 11 wherein said synchronization signal generator further includes a synchronization signal separator receiving said main picture signal and separating a main synchronization signal therefrom to form said first synchronization signal. .Iaddend.   
     
     
        .Iadd.13.  The picture-in-picture circuit of claim 10 further comprising an analog switch for time division multiplexing said synchronized sub-picture signal with said main picture signal to produce picture-in-picture. .Iaddend. .Iadd.14. The picture-in-picture circuit of claim 10 wherein said color synchronizer includes, a main picture Y-C separator producing a main color subcarrier signal,   a phase lock loop connected to the output of said main Y-C separator, synchronized in phase therewith and developing first and second carrier signals separated in phase by 90 degrees, and   first and second time delays connected to the phase locked loop and receiving said first and second carrier signals, said first and second time delays delaying said first and second carrier signals to produce first and second color sub-picture synchronization signals. .Iaddend. .Iadd.15. The picture-in-picture circuit of claim 10 wherein said color synchronizer includes,   a main picture Y-C separator producing a main color subcarrier signal,   a first phase lock loop connected to said main Y-C separator and locking to the phase of said main color subcarrier signal,   a second phase lock loop connected to the output of said chrominance modulator and mocking to the phase of said sub-pi picture color subcarrier signal,   a phase detector for determining the phase difference between said main color subcarrier signal and said sub-picture color subcarrier signal, and   a voltage controlled oscillator responsive to the phase difference determined by said phase detector and producing first and second phase shift signals as first and second color sub-picture synchronization   
     
     
        signals. .Iaddend. .Iadd.16.  The picture-in-picture circuit of claim 10 wherein said color synchronizer includes, a main picture Y-C separator producing a main color subcarrier signal,   a main picture burst signal extraction circuit extracting a main burst signal from the main color subcarrier signal,   a sub-picture burst signal extracting circuit extracting the sub-picture burst signal from the sub-picture color subcarrier signal,   a phase detector for determining the phase difference between said main burst signal and said sub-picture burst signal, and   a voltage controlled oscillator responsive to the phase difference determined by said phase detector and producing first and second phase shift signals as first and second color sub-picture synchronization signals. .Iaddend. .Iadd.17. The picture-in-picture circuit of claim 15 wherein said synchronization signal generator includes,   a synchronization signal separator receiving said main picture signal and separating a main synchronization signal therefrom to form a memory synchronization signal;   an independent synchronization signal generator generating a synchronization signal independent of any picture signal,   missing synchronization signal detector for determining if the main picture signal is missing a main synchronization signal and producing a missing signal indicative thereof,   first means, responsive to receipt of said missing signal from said missing synchronization signal detector, for supplying said synchronization signal from said independent synchronization signal generator as said memory synchronization signal, said reader reading the output of said memory under control of said memory synchronization signal, and   second means, responsive to receipt of said missing signal from said missing synchronization signal detector, for supplying a voltage indicative of a reference phase difference to said voltage controlled oscillator,   said first and second means, when responsive to receipt of a missing signal allowing the sub-picture to be generated in the absence of a main picture. .Iaddend.