Control apparatus for a color television receiver

Abstract

A color reference signal is inserted during the vertical blanking interval of a transmitted television waveform, for utilization by the described apparatus in automatically setting the hue and saturation of the display of an NTSC or a PAL receiver. The apparatus responds to the transmitted burst signal to set the frequency and phase of the sub-carrier oscillator of the receiver and, further, to the transmitted reference signal to correct any such inaccurate setting of phase as is caused by adverse conditions of networking and transmission from the studio to the receiver.

Description

FIELD OF THE INVENTION

This invention relates to color television receivers and, more particularly, to a modification of the apparatus described in Ser. No. 121,842 application, above-noted patent a color reference signal inserted in the vertical blanking interval may additionally contain amplitude information which can be utilized at the receiver to automatically correct the saturation of its reproduced display under conditions where the amplitude of the synchronizing burst does not accurately represent the correct relative amplitude of the chrominance signal. As there pointed out, this inaccurate representation may be due to an incorrect burst amplitude setting at the signal source, to differential amplitude distortion in networking and transmission, to multipath, to antenna transmission line reflections, etc. Under such adverse conditions, a color reference signal would be more representative of the proper relative amplitude of the chrominance signal since it will undergo the same types of distortion as will the chrominance signal itself.

However, use of the reference signal information alone in providing a primary source of automatic chroma control voltage (ACC) for the correction may exhibit the disadvantage that the speed of the offered correction is relatively slow because the reference signal is transmitted at the slower field or frame rate. In accordance with the present invention, on the other hand, such correction can be improved by using the burst amplitude in obtaining the prime source of ACC voltage, and using the amplitude of the reference signal to adjust the control in much the same way that the reference phase was used to adjust the demodulating signal phase in FIG. 2. Thus, whereas the phase of the demodulating signal was first set by the phase of the color synchronizing burst in FIG. 2 and then corrected at a slower rate by the phase of the color reference bar, so too may the amplitude of the ACC voltage be first set by the amplitude of the color burst and any needed adjustment be done by the slower rate reference signal amplitude. Such adjustment will follow the use--in FIG. 2, for example--of an amplitude comparator 72, which provides an output correction voltage whenever there exists a difference between the amplitude of the recovered synchronizing burst (applied to a first of its input terminals from the synchronizing system 50) and the amplitude of the recovered reference signal (applied to a second of its input terminals from the gated amplifier 56).

While there have been described what are considered to be preferred embodiments of the present invention, it will be readily apparent that modifications may be made without departing from the spirit and scope of the instant disclosure. Thus, while the color reference signal has been described as being of the BTS Committee format, it will be recognized that other type signals--such as the type described in the aforenoted Ser. No. 121,842 application--might be used as well, and still utilize the teachings herein. Similarly, while the color reference bar 12 of FIG. 1 has been described as being of --(R-Y) phase for the BTS format, it will be appreciated that with only minor modifications to the apparatus connections, a phase of --(R-Y) phase will also be applicable.

It will also be noted that the gating apparatus described herein in comparing the phase of the oscillator signal with the phase of the VIR reference or in sensing the output of one of the color demodulators at the time of reference signal insertion in the vertical blanking waveform is far simpler than the approach suggested by U.S. Pat. No. 3,456,068--Wilhelmy. Besides further representing an improvement over the apparatus of that patent in providing for automatic saturation control in addition to hue control, the construction of the present invention offers its correction features with a higher signal-to-noise ratio than is there present, by virtue of its use of a reference signal of substantially longer duration. Utilization of such reference signal to occupy almost an entire line interval in the vertical blanking waveform--rather than just at the end of a horizontal scanning line as in U.S. Pat. No. 3,456,068--also offers the advantage that phase shifts caused by adverse transmission characteristics are much less severe and, therefore, easier to work with.

Claims

1. In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal and being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component and produce color difference signals containing information proportional to the hue and saturation of the televised scene, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of such bursts and to lock the phase of the oscillatory signal to the phase of said bursts;

second means, including at least first and second chrominance demodulators responsive to said oscillatory signal, and also responsive to said television signal, for demodulating said chrominance component and producing color difference signal outputs representative of the hue and saturation of the televised scene;

second third means, also responsive to said television signal, for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal; and

third fourth means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal, said fourth means comprising a variable phase shifter, external to said first means, and interposed between an output of said first means and said demodulators;

whereby the degree of error in the hue of a reproduced color image attributable to such transmission characteristics as multipath, transmission line reflection and the like is correspondingly reduced

said apparatus also including fifth means for coupling the chrominance component of said television signal to said demodulators for demodulation with said phase-adjusted oscillatory signal to produce said color difference signals; and

sixth means responsive to said longer duration color reference signal and said color synchronizing bursts for varying the gain of said fifth means as a function of the amplitudes of said bursts and said reference signal.

2. The apparatus of claim 1 wherein there is additionally included fourth means for coupling the chrominance component of said television signal for demodulation with said phase-adjusted oscillatory signal to produce said color difference signals, and wherein fifth means is also included to respond to corresponding coupling of said longer duration color reference signal to control the amplitude of said color difference signals and the saturation of the reproduced color image

as a function of the amplitude of said reference signal. 3. The apparatus of claim 1 In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal and being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of such bursts and to lock the phase of the oscillatory signal to the phase of said bursts;

second means, including at least first and second chrominance demodulators responsive to said oscillatory signal, and also responsive to said television signal, for demodulating said chrominance component and producing color difference signal outputs representative of the hue and saturation of the televised scene;

third means, also responsive to said television signal for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal;

fourth means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal, said fourth means comprising a variable phase shifter, external to said first means, and interposed between an output of said first means and said demodulators;

and fifth means coupled to said third means for providing a DC correction signal to alter the control signal to which said fourth means responds, with said correction signal being controllable to adjust the hue of a reproduced color image in accordance with individual viewing preference;

whereby the degree of error in the hue of a reproduced color image attributable to such transmission characteristics as multipath, transmission line reflection and the like is correspondingly reduced; wherein there is additionally included fourth sixth means for coupling the chrominance component of said television signal for demodulation with said phase-adjusted oscillatory signal to produce said color difference signals, and wherein fifth seventh means is also included to respond to corresponding coupling of said longer duration color reference signal and said color synchronizing bursts to vary the gain of said sixth means to control the amplitude of said color difference signals and the saturation of the reproduced color image as a function of

the amplitude of said reference signal. 4. The apparatus of claim 1 wherein said second third means includes a phase comparator coupled to compare the phase of the oscillatory signal provided by said first means with the phase of said recovered longer duration color reference signals, and for providing said control signal as being representative of the degree to which the phase of said oscillatory signal

differs from the phase of said reference signal. 5. The apparatus of claim 1 wherein said third means includes an amplifier coupled to receive said color difference signals produced by one of said demodulators and gated during the prescribed interval during the vertical retrace portion of the television signal in which said longer duration color reference signal is inserted, for developing said control signal for adjusting the phase of the oscillatory signal provided by said first means as being representative of the amplitude of said color difference signals

during said prescribed interval. 6. The apparatus of claim 1 wherein there is additionally included fourth seventh means coupled to said second third means for providing a direct current correction signal to alter the said control signal, said seventh means comprising a source of direct current and a potentiometer coupled thereto, said potentiometer having an adjustable tap, with adjustment of said tap varying the magnitude of said direct current correction signal to control the alteration of said control voltage and thereby the phase shift imparted to said oscillatory signal by said interposed phase shifter representative of the phase difference between said oscillatory signal and said longer duration reference signal, with said correction signal being controlable to adjust the hue of a reproduced

color image in accordance with individual viewing preference. 7. The apparatus of claim 1 for use in a color television receiver providing color difference signals along B-Y and R-Y demodulation axes and operative with a television signal including said longer duration color reference signal at --(B-Y) phase, wherein said second third means includes means for monitoring the amplitude of the color difference signals provided along said R-Y demodulation axis and to develop said control signal for said third fourth means to adjust the phase of said oscillatory signal to reduce the amplitude of said R-Y color difference signal during the occurrence of said longer duration color reference signal in a direction to automatically compensate for transmission characteristic changes as would adversely affect the hue of the reproduced color image.

The apparatus of claim 1 for use in a color television receiver providing color difference signals along R-Y and B-Y demodulation axes and operative with a television signal including said longer duration color reference signal at --(R-Y) phase, wherein said second third means includes means for monitoring the amplitude of the color difference signals provided along said B-Y demodulation axis and to develop said control signal for said third fourth means to adjust the phase of said oscillatory signal to reduce the amplitude of said B-Y color difference signal during the occurrence of said longer duration color reference signal in a direction to automatically compensate for transmission characteristic changes as would adversely affect the hue of the reproduced color image. 9. In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal and being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of such bursts and to lock the phase of the oscillatory signal to the phase of said bursts;

second means, including at least first and second chrominance component demodulators responsive to said oscillatory signal, and also responsive to said television signal, for demodulating said chrominance component and producing color difference signal outputs representative of the hue and saturation of the televised scene;

third means, also responsive to said television signal, for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal;

fourth means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal; and

fifth means for selectively altering the control signal to which said fourth means responds, said fifth means comprising means for utilizing a DC correction signal developed with independence of the phase of said reference signal to alter the control signal developed as a function of the phase of said reference signal, with said correction signal being controllable to adjust the hue of a reproduced color image,

whereby the degree of error in the hue of a reproduced color image attributable to such transmission characteristics as multipath, transmission line reflection and the like is correspondingly

reduced. 10. In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal and being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of such bursts and to lock the phase of the oscillatory signal to the phase of said bursts, said first means including a reference oscillator synchronized in frequency and phase by said bursts;

second means, including at least first and second chrominance component demodulators responsive to said oscillatory signal, and also responsive to said television signal, for demodulating said chrominance component and producing color difference signal outputs representative of the hue and saturation of the televised scene;

third means, also responsive to said television signal, for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal;

said third means comprising means for sensing the output of one of said demodulators during the occurrence of said reference signal and deriving a control voltage therefrom;

fourth means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal;

said fourth means comprising a variable phase shifter, external to said oscillator, and interposed between an output of said oscillator and said demodulators;

fifth means for coupling the chrominance component of said television signal to said demodulators for demodulation with said phase-adjusted oscillatory signal to produce color difference signals, said fifth means also effecting a coupling of said reference signal to said demodulators; and

sixth means responsive to said longer duration color reference signals and said color synchronizing bursts for varying the gain of said fifth means to control the amplitude of the color difference signals and the saturation of the reproduced image as a function of the amplitude of said

reference signals and said synchronizing bursts. 11. In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal, said reference signal being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component and produce color difference signals containing information proportional to the hue and saturation of the televised scene, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of said bursts and to lock the phase of the oscillatory signal to the phase of said bursts;

said first means including a reference oscillator synchronized in frequency and phase by said bursts;

second means, including at least first and second chrominance component demodulators responsive to said oscillatory signal, and also responsive to said television signal, for demodulating said chrominance component and producing color-difference signal outputs representative of the hue and saturation of the televised scene;

third means, also responsive to said television signal, for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal;

fourth means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal;

said fourth means comprising a variable phase shifter, external to said oscillator, and interposed between an output of said oscillator and said demodulators;

fifth means for coupling the chrominance component of said television signal for demodulation with said phase-adjusted oscillatory signal to produce said color difference signals;

sixth means responsive to said longer duration color reference signal and said color synchronizing bursts for varying the gain of said fifth means to control the amplitude of said color difference signals and the saturation of the reproduced color image as a function of the amplitude of said reference signal; and

seventh means for selectively altering the control signal to which said fourth means responds, said seventh means comprising eighth means, including a source of direct current and a potentiometer coupled thereto, said potentiometer having an adjustable tap, for developing a DC correction voltage with independence of the phase of said reference signal; and

ninth means for utilizing said DC correction voltage to alter the control voltage developed by said third means, with the magnitude of said DC correction voltage varying in response to adjustment of said tap to adjust the hue of a reproduced color image in accordance with individual viewer preference;

whereby the degree of error in the hue of a reproduced color image attributable to such transmission characteristics as multipath, transmission line reflection and the like is correspondingly

reduced. 12. In a color television receiver adapted to receive a television signal including a luminance component, a chrominance component modulated in both phase and amplitude, periodically, recurring color synchronizing bursts occupying prescribed intervals during the horizontal retrace portions of said signal and a color reference signal occupying a prescribed interval during the vertical retrace portion of said television signal, said reference signal being of substantially longer duration than said color synchronizing bursts, apparatus comprising:

first means for providing an oscillatory signal to demodulate said chrominance component and produce color difference signals containing information proportional to the hue and saturation of the televised scene, said means being responsive to the television signal for recovering the color synchronizing bursts thereof and for utilizing said bursts to lock the frequency of the oscillatory signal to the frequency of said bursts and to lock the phase of the oscillatory signal to the phase of said bursts;

second means, also responsive to said television signal, for recovering said longer duration color reference signal and for utilizing said signal in developing a control signal to adjust the phase of said oscillatory signal as a function of the phase of said reference signal;

third means responsive to said oscillatory signal and to said control signal for varying the phase of said oscillatory signal in a direction to correspond with the phase of said reference signal as represented by said control signal; and

fourth means coupled to said second means for providing a correction signal to alter the control signal representative of the phase difference between said oscillatory signal and said longer duration reference signal, with said correction signal being controllable to adjust the hue of a reproduced color image in accordance with individual viewing preference;

whereby the degree of error in the hue of a reproduced color image attributable to such transmission characteristics as multipath, transmission line reflection and the like is correspondingly reduced.