Fast acting phase shifting apparatus for use in digital sampling systems

Abstract

A method and apparatus is disclosed for controlling the sampling of a composite analog color video signal so that the analog signal is sampled at precise locations relative to the phase of the color subcarrier of the color video signal in the absence of modulation. The invention thereby enables a digitized signal having a constant phase relationship relative to the unmodulated subcarrier phase to be provided which can be advantageously used in magnetic recording and reproducing apparatus. Since the constancy of the location of the samples relative to the phase of the color burst is maintained prior to recording, there is no phase error that would pose a problem during reproducing of the signal. The apparatus stores a set of reference samples of a selected number of cycles of the color burst interval of the color video signal and generates an output clock signal that is phase synchronized with the reference samples, subsequently stores sets of comparison samples of color burst cycles from subsequent horizontal video lines using the generated clock signal and detects any error in the phase location thereof. The apparatus adjusts the phase of the generated output clock signal in response to any detected error signal and stores a new set of reference samples in the event that the error detected is beyond predetermined limits.

What is claimed is: 
     
       1. A method of sampling a composite analog color television signal whereby the samples are taken at precise locations in the television signal relative to the phase of the color burst thereof, comprising the steps of: storing reference samples obtained from color burst cycles of a horizontal television line at times determined by a phase stable signal and generating an output clock signal that is phase synchronized with said reference samples;   sampling the color burst of subsequent horizontal television lines at times determined by said output clock signal and storing a set of comparison samples of color burst cycles;   examining each set of stored comparison samples of color burst cycles and detecting a change in the sample phase location thereof and providing an error signal indicative of the magnitude of the change;   adjusting the phase of the generated output clock signal in response to the error signal when the magnitude of the phase change is within a predetermined limit; and,   storing new reference samples of color burst cycles when said magnitude of phase change exceeds said predetermined limit and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       2. A method as defined in claim 1 wherein the television signal is sampled at a rate that is three times the frequency of the color subcarrier of said analog color television signal. 
     
     
       3. A method as defined in claim 2 wherein the television signal is sampled at phase locations for each cycle of the subcarrier, relative to the 0°, 120° and 240° phase locations of the color burst. 
     
     
       4. A method as defined in claim 1 wherein said comparison samples that are stored and examined are taken from color burst cycles occurring during the next succeeding horizontal television line following the line from which said reference samples are taken and thereafter during alternate succeeding horizontal television lines. 
     
     
       5. A method of sampling a composite analog color television signal whereby the samples are taken in precise locations in the television signal relative to the phase of the color burst thereof, comprising the steps of: storing reference samples obtained from color burst cycles of a horizontal television line at times determined by a phase stable signal and generating an output clock signal that is phase synchronized with said reference samples;   sampling the color burst of subsequent horizontal lines at times determined by said output clock signal and storing a set of comparison samples of color burst cycles;   examining each set of stored comparison samples of color burst cycles and detecting a change in the sample phase location thereof and providing an error signal indicative of the magnitude of the phase change; and   adjusting the phase of the generated output clock signal in response to the error signal.   
     
     
       6. A method of sampling a composite analog color television signal whereby the samples are taken in precise locations in the television signal relative to the phase of the color burst thereof, comprising the steps of: storing reference samples obtained from color burst cycles of a horizontal television line at times determined by a phase stable signal and generating an output clock signal that is phase synchronized with said reference samples;   sampling the color burst of subsequent horizontal television lines at times determined by said output clock signal and storing a set of comparison samples of color burst cycles;   examining each set of stored comparison samples of color burst cycles and detecting a change in the sample phase location thereof; and,   storing new reference samples of color burst cycles when a phase change is detected and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       7. A method of sampling a composite analog color television signal whereby the samples are taken in precise locations in the television signal relative to the phase of the color burst thereof, comprising the steps of: storing reference samples obtained from color burst cycles of a horizontal television line at times determined by a phase stable signal and generating an output clock signal that is phase synchronized with said reference samples;   sampling the color burst of subsequent horizontal television lines at times determined by said output clock signal and storing a set of comparison samples of color burst cycles;   examining each set of stored comparison samples of color burst cycles and detecting a change in the sample phase location thereof; and,   storing new reference samples of color burst cycles when a phase change that exceeds a predetermined magnitude is detected and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       8. Apparatus for generating an output clock signal that is phase synchronized to the color burst of a composite analog color television signal having a color subcarrier component for use in sampling the analog color television signal, comprising: means for sampling said analog color television signal at times determined by a clock signal having a sampling rate that is a multiple of the frequency of said color subcarrier component and generating samples of said analog color television signal;   means for storing reference samples of color burst cycles of a horizontal line of the color television signal generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of color burst cycles from subsequent horizontal lines of said color television signal generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of each set of stored comparison samples and the phase of the reference samples and generating an error signal indicative of the magnitude of any phase change;   means for adjusting the phase of the generated output clock signal in response to the error signal generated when the magnitude of the phase change is within predetermined limits; and,   means for activating said reference sample storing means to store new reference samples of burst cycles in response to the magnitude of said error signal being outside of said predetermined limits and thereby generate a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       9. Apparatus as defined in claim 8 wherein said means for storing said sets of comparison samples is controlled to store said samples from color burst cycles that occur during subsequent and alternately succeeding horizontal lines. 
     
     
       10. Apparatus as defined in claim 8 wherein said sampling rate is three times the frequency of the color subcarrier component of said analog color television signal. 
     
     
       11. Apparatus as defined in claim 10 wherein said sampling means samples said analog color television signal at phase locations corresponding to the 0°, 120° and 240° phase locations of said color burst. 
     
     
       12. Apparatus as defined in claim 11 wherein said phase change detecting means comprises: means for arithmatically adding the values of said 120° and 240° sample locations of said color burst to provide a resultant value, and   means for comparing said resultant value with the value of said 0° sample location of said color burst and providing an error signal having a magnitude that is proportional to the difference therebetween.   
     
     
       13. Apparatus for controlling the phase locations of the sampling of a composite analog color television signal which is sampled rate that is a multiple of the frequency of the color subcarrier component of said analog color television signal, comprising: means for sampling said analog color television signal at said sampling rate and at specific locations determined by a clock signal applied thereto and generating samples of said analog color television signal;   first means for storing a set of reference samples of color burst cycles of a horizontal line generated by said sampling means when the clock signal applied thereto is phase stable and generating an output clock signal therefrom that is phase synchronized with said reference samples;   means for adjusting the phase of said generated output clock signal in response to phase error signals being applied thereto;   second means for storing a set of comparison samples of said color burst cycles from the color burst of subsequent horizontal lines generated by said sampling means when the clock signal applied thereto is the phase adjusted output clock signal from said phase adjusting means;   means coupled to said second sample storing means for examining the comparison samples stored therein and for generating phase error signals in response to the detection of any phase differences between the phase of said reference samples and the phase of said comparison samples and applying said phase error signals to said phase adjusting means;   means for monitoring said error signals and for activating said first storing means to store a new set of reference samples of color burst cycles in the event the error signal exceeds a predetermined limit.   
     
     
       14. Apparatus as defined in claim 13 wherein said sampling means samples said analog color television signal at the phase locations corresponding to the 0°, 120° and 240° phase locations of said color burst. 
     
     
       15. Apparatus as defined in claim 14 wherein said examining and error signal generating means comprises: means for arithmatically adding the values of said comparison samples taken at 120° and 240° sample locations of said color burst to obtain a first resultant value, and   means for comparing said first resultant value with the value of said comparison sample taken at 0° sample location of said color burst and providing an error signal when said first resultant value and said sample value of said 0° sample location are unequal.   
     
     
       16. Apparatus as defined in claim 15 wherein said error signal monitoring means comprises level detecting means adapted to provide an activating signal to said first storing means when the magnitude of said error signal exceeds said predetermined limit. 
     
     
       17. Apparatus for generating an output clock signal that is phase synchronized to the color burst of a composite analog color television signal having a color subcarrier component for use in sampling the analog color television signal, comprising: means for sampling said analog color television signal at times determined by a clock signal having a sampling rate that is a multiple of the frequency of the color subcarrier component and generating samples of said analog color television signal;   .[.means for storing reference samples of color burst cycles of a horizontal line of the television signal generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;.].   means for .[.storing sets of.]. .Iadd.generating .Iaddend.comparison samples of color burst cycles from .[.subsequent.]. horizontal lines of the television signal generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of .[.each set of stored.]. .Iadd.the .Iaddend.comparison samples and the phase of the .[.reference samples.]. .Iadd.output clock signal .Iaddend.and generating an error signal indicative of the magnitude of any phase change; and   means for adjusting the phase of the generated output clock signal in response to the error signal.   
     
     
       18. Apparatus for generating an output clock signal that is phase synchronized to the color burst of a composite analog color television signal having a color subcarrier component for use in sampling the analog color television signal, comprising: means for sampling said analog color television signal at times determined by a clock signal having a sampling rate that is a multiple of the frequency of the color subcarrier component and generating samples of said analog color television signal;   means for storing reference samples of color burst cycles of a horizontal line of the television signal generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of color burst cycles from subsequent horizontal lines of the television signal generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of each set of stored comparison samples and the phase of the reference samples; and   means for activating said reference sample storing means to store new reference samples of burst cycles in response to the detection of a phase change and thereby generate a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       19. Apparatus for generating an output clock signal that is phase synchronized to the color burst of a composite analog color television signal having a color subcarrier component for use in sampling the analog color television signal, comprising: means for sampling said analog color television signal at times determined by a clock signal having a sampling rate that is a multiple of the frequency of the color subcarrier component and generating samples of said analog color television signal;   means for storing reference samples of color burst cycles of a horizontal line of the television signal generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of color burst cycles from subsequent horizontal lines of the television signal generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of each set of stored comparison samples and the phase of the reference samples; and   means for activating said reference sample storing means to store new reference samples of burst cycles in response to the detection of a phase change that exceeds a predetermined magnitude and thereby generate a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       20. A method of sampling an information signal having a time-base synchronizing component of a known frequency whereby the samples are taken in precise locations relative to the synchronizing component thereof, comprising the steps of: storing reference samples obtained from said synchronizing component at times determined by a phase stable clock signal and generating an output clock signal that is phase synchronized with said reference samples; periodically sampling the synchronizing component at times determined by said output clock signal to obtain a set of comparison samples thereof;   examining each set of comparison samples and detecting a change in the sample phase location thereof and providing an error signal indicative of the magnitude of the change;   adjusting the phase of the generated output clock signal in response to the error signal when the magnitude of the phase change is within a predetermined limit; and   storing new reference samples of said synchronizing component when said magnitude of phase change exceeds said predetermined limit and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       21. A method of sampling an information signal having a time-base synchronizing component of a known frequency whereby the samples are taken in precise locations relative to the synchronizing component thereof, comprising the steps of: storing reference samples obtained from said synchronizing component at times determined by a phase stable clock signal and generating an output clock signal that is phase synchronized with said reference samples;   periodically sampling the synchronizing component at times determined by said output clock signal to obtain a set of comparison samples thereof;   examining each set of comparison samples and detecting a change in the sample phase location thereof and providing an error signal indicative of the magnitude of the change; and   adjusting the phase of the generated output clock signal in response to the error signal.   
     
     
       22. A method of sampling an information signal having a time-base synchronizing component of a known frequency whereby the samples are taken in precise locations relative to the synchronizing component thereof, comprising the steps of: storing reference samples obtained from said synchronizing component at times detemined by a phase stable clock signal and generating an output clock signal that is phase synchronized with said reference samples;   periodically sampling the synchronizing component at times determined by said output clock signal to obtain a set of comparison samples thereof;   examining each set of comparison samples and detecting a change in the sample phase location thereof; and   storing new reference samples of said synchronizing component when a change is detected and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       23. A method of sampling an information signal having a time-base synchronizing component of a known frequency whereby the samples are taken in precise locations relative to the synchronizing component thereof, comprising the steps of: storing reference samples obtained from said synchronizing component at times determined by a phase stable clock signal and generating an output clock signal that is phase synchronized with said reference samples;   periodically sampling the synchronizing component at times determined by said output clock signal to obtain a set of comparison samples thereof;   examining each set of comparison samples and detecting a change in the sample phase location thereof; and   storing new reference samples of said synchronizing component when a phase change that exceeds a predetermined magnitude is detected and generating a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       24. Apparatus for generating an output clock signal that is phase synchronized to a time-base synchronizing component of a known frequency associated with an information signal for use in sampling the information signal, comprising: means for sampling said synchronizing component at times determined by a clock signal having a sampling rate that is a multiple of the frequency of said synchronizing component and generating samples thereof;   means for storing reference samples of said synchronizing component generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of said synchronizing components generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of the comparison samples and the phase of the reference samples and generating any error signal indicative of the magnitude of an phase change;   means for adjusting the phase of the generated output clock signal in response to the error signal generated when the magnitude of the phase change is within predetermined limits; and   means for activating said reference sample storing means to store new reference samples of said synchronizing component in response to the magnitude of said error signal being outside of said predetermined limits and thereby generate a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       25. Apparatus for generating an output clock signal that is phase synchronized to a time-base synchronizing component of a known frequency associated with an information signal for use in sampling the information signal, comprising: means for sampling said synchronizing component at times determined by .[.a.]. .Iadd.said output .Iaddend.clock signal having a sampling rate that is a multiple of the frequency of said synchronizing component and generating samples thereof;   .[.means for storing reference samples of said synchronizing component generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples.].   means for .[.storing sets of.]. .Iadd.generating .Iaddend.comparison samples of said synchronizing component generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of the comparison samples and the phase of the said .[.reference samples.]. .Iadd.output clock signal .Iaddend.and generating an error signal indicative of the magnitude of any phase change; and   means for adjusting the phase of the generated output clock signal in response to the error signal.   
     
     
       26. Apparatus for generating an output clock signal that is phase synchronized to a time-base synchronizing component of a known frequency associated with an information signal for use in sampling the information signal, comprising: means for sampling said synchronizing component at times determined by a clock signal having a sampling rate that is a multiple of the frequency of said synchronizing component and generating samples thereof;   means for storing reference samples of said synchronizing component generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of said synchronizing component generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of the comparison samples and the phase of the reference samples; and   means for activating said reference samples storing means to store new reference samples of said synchronizing component when a phase change is detected and thereby generate a new output clock signal that is phase synchronized with said new reference samples.   
     
     
       27. Apparatus for generating an output clock signal that is phase synchronized to a time-base synchronizing component of a known frequency associated with an information signal for use in sampling the information signal, comprising: means for sampling said synchronizing component at times determined by a clock signal having a sampling rate that is a multiple of the frequency of said synchronizing component and generating samples thereof;   means for storing reference samples of said synchronizing component generated by said sampling means clocked by a phase stable clock signal and generating said output clock signal that is phase synchronized with said reference samples;   means for storing sets of comparison samples of said synchronizing component generated by said sampling means clocked by said output clock signal;   means for detecting a change between the phase of the comparison samples and the phase of the reference samples; and   means for activating said reference sample storing means to store new reference samples of said synchronizing component in response to the detection of a phase change that exceeds a predetermined magnitude and thereby generate a new output clock signal that is phase synchronized with said new reference samples. .Iadd.   
     
     
       28.  In a system for digitizing a color television signal wherein the color television signal is sampled with a sampling signal whose rate is a multiple of the burst signal frequency and each sample is converted to a corresponding digital signal, a method for controlling the phase of the sampling signal comprising the steps of obtaining at least three samples of the burst signal including in said color television signal;   determining a reference sampling phase as a function of at least two of said samples by deriving a calculated sample level from said at least two samples;   sensing a phase error between the actual sampling phase of said sampling signal and said reference sampling phase by detecting the difference between said calculated sample level and the level of a predetermined one of said at least three samples; and   adjusting the phase of said sampling signal in accordance with said detected difference in a direction to reduce said detected difference to a null value. .Iaddend. .Iadd.29. The method of claim 28 wherein said predetermined sample differs from both of said at least two samples. .Iaddend. .Iadd.30. The method of claim 29 wherein the rate of said sampling signal is an even multiple of twice the burst signal frequency.   
     
     
        .Iaddend. .Iadd.31.  The method of claim 28 wherein said step of adjusting the phase of said sampling signal comprises generating a control voltage, changing the magnitude of said control voltage by an incremental amount during each period of said burst signal, the change being a function of whether the level of said predetermined one sample exceeds or is less than said calculated sample level;   and adjusting the phase of said sampling signal in accordance with said control voltage. .Iaddend. .Iadd.32. A method of determining whether the burst signal of a color television signal is sampled in a predetermined phase relationship, comprising the steps of   sampling said burst signal at a rate which is a multiple of the burst signal frequency;   determining a theoretical sample level of said burst signal as a function of a plurality of the actual sample levels thereof, said theoretical sample level representing a sample level that would be obtained if said burst signal is sampled in said predetermined phase relationship; and   detecting the difference between said theoretical sample level and a predetermined one of said actual sample levels. .Iaddend. .Iadd.33. The method of claim 32 wherein said step of determining a theoretical sample level of said burst signal comprises   obtaining the difference between two actual sample levels; and multiplying said difference by a predetermined constant. .Iaddend. .Iadd.34. Apparatus for use in a digital encoder for a color television signal, comprising   sampling pulse generating means for generating sampling pulses with a rate that is a multiple of the burst signal frequency of said color television signal;   sampling means responsive to said sampling pulses for sampling said color television signal, including said burst signal, and for digitizing each sample;   theoretical sample level producing means for producing a theoretical sample level of said burst signal as a function of at least two actual samples thereof, said theoretical sample level representing a sample that would be obtained if said burst signal is sampled by sampling pulses which exhibit a predetermined phase with respect thereof;   phase difference determining means for determining the difference between the actual phase of said sampling pulses and said predetermined phase in accordance with the difference between said theoretical sample level and an actual sample; and   adjusting means responsive to said determined phase difference to adjust the phase of said sampling pulses so as to reduce said determined phase   
     
     
        difference to a null value. .Iaddend. .Iadd.35.  The apparatus of claim 34 wherein the rate of said sampling pulses is an even multiple of twice the burst signal frequency. .Iaddend. .Iadd.36. The apparatus of claim 35 wherein said adjusting means comprises   control voltage generating means for generating a control voltage to control the phase of said sampling pulses; and   means for changing said control voltage in accordance with said difference between said theoretical sample level and an actual sample. .Iaddend. .Iadd.37. The apparatus of claim 36 wherein said means for changing said control voltage comprises   means for increasing said control voltage by an incremental amount during a period of said burst signal when said theoretical sample level exceeds said actual sample; and   means for decreasing said control voltage by said incremental amount during a period of said burst signal when said theoretical sample level is less   
     
     
        than said actual sample. .Iaddend. .Iadd.38.  The apparatus of claim 37 further comprising capacitance means; and wherein said means for increasing said control voltage comprises charging means for charging said capacitance means for a predetermined duration, and   said means for decreasing said control voltage comprises discharge means for discharging said capacitance means for said predetermined duration. .Iaddend. .Iadd.39. Apparatus for determining if the burst signal of a color television signal is sampled at a predetermined phase angle thereof, comprising sampling means for sampling said burst signal at a rate that is a multiple of the burst signal frequency; theoretical sample level producing means for producing a theoretical sample level of said burst signal as a function of a plurality of the actual sample levels thereof, said theoretical sample level representing a sample that would be obtained if said burst signal is sampled at said predetermined phase angle; and determining means responsive to said theoretical sample level and a predetermined one of said actual sample levels for determining whether an actual sample of said burst signal is produced at said predetermined phase   
     
     
        angle. .Iaddend. .Iadd.40.  In a system for digitizing a color television signal wherein the color television signal is sampled with a sampling signal whose rate is a multiple of the burst signal frequency and each sample is converted to a corresponding digital signal, a method for controlling the phase of the sampling signal comprising the steps of obtaining at least three samples of the burst signal included in said color television signal; determining a sampling phase as a function of at least two of said samples by deriving a calculated sample level from said at least two samples; sensing a phase error between the actual sampling phase of said sampling signal and said sampling phase by detecting the difference between said calculated sample level and the level of a predetermined one of said at least three samples; and adjusting the phase of said sampling signal in accordance with said detected difference in a direction to reduce said detected difference to a null value. .Iaddend. .Iadd.41. The method of claim 40 wherein said predetermined sample differs 
     
     
        from both of said at least two samples. .Iaddend. .Iadd.42.  The method of claim 41 wherein the rate of said sampling signal is an even multiple of twice the burst signal frequency. .Iaddend. .Iadd.43. The method of claim 1 wherein said step of adjusting the phase of said sampling signal comprises generating a control voltage, changing the magnitude of said control voltage by an incremental amount during each period of said burst signal, the change being a function of whether the level of said predetermined one sample exceeds or is less than said calculated sample level; and adjusting the phase of said sampling signal in accordance with said control voltage. .Iaddend. .Iadd.44. A method of determining whether the burst signal of a color television signal is sampled in a predetermined phase relationship, comprising the steps of sampling said burst signal at a rate which is a multiple of the burst signal frequency; determining a sample level of said burst signal as a function of a plurality of the actual sample levels thereof, said sample level representing a sample level that would be obtained if said burst signal is sampled in said predetermined phase relationship; and detecting the difference between said sample level and a predetermined one of said actual sample levels. .Iaddend. .Iadd.45. The method of claim 44 wherein said step of determining a sample level of said burst signal comprises obtaining the difference between two actual sample levels; and multiplying said difference by a predetermined constant. .Iaddend. .Iadd.46. Apparatus for use in a digital encoder for a color television signal, comprising sampling pulse generating means for generating sampling pulses with a rate that is a multiple of the burst signal frequency of said color television signal; sampling means responsive to said sampling pulses for sampling said color television signal, including said burst signal, and for digitizing each sample; sample level producing means for producing a sample level of said burst signal as a function of at least two actual samples thereof, said sample level representing a sample that would be obtained if said burst signal is sampled by sampling pulses which exhibit a predetermined phase with respect thereof; phase difference determining means for determining the difference between the actual phase of said sampling pulses and said predetermined phase in accordance with the difference between said sample level and an actual sample; and adjusting means responsive to said determined phase difference to adjust the phase of said sampling pulses so as to reduce said determined phase difference to a null value. .Iaddend. .Iadd.47. The apparatus of claim 46 wherein the rate of said sampling pulses is an even multiple of twice the burst signal frequency. .Iaddend. .Iadd.48. The apparatus of claim 46 wherein said adjusting means comprises control voltage generating means for generating a control voltage to control the phase of said sampling pulses; and means for changing said control voltage in accordance with said difference between said sample level and an actual sample. .Iaddend. .Iadd.49. The apparatus of claim 48 wherein said means for changing said control voltage comprises means for increasing said control voltage by an incremental amount during a period of said burst signal when said sample level exceeds said actual sample; and means for decreasing said control voltage by said incremental amount during a period of said burst signal when said sample level is less than said actual sample. .Iaddend. .Iadd.50. The apparatus of claim 49 further comprising capacitance means; and wherein said means for increasing said control voltage comprises charging means for charging said capacitance means for a predetermined duration, and said means for decreasing said control voltage comprises discharge means for discharging said capacitance means for said predetermined duration. .Iaddend. .Iadd.51. Apparatus for determining if the burst signal of a color television signal is sampled at a predetermined phase angle thereof, comprising sampling means for sampling said burst signal at a rate that is a multiple of the burst signal frequency; sample level producing means for producing a sample level of said burst signal as a function of a plurality of the actual sample levels thereof, said sample level representing a sample that would be obtained if said burst signal is sampled at said predetermined phase angle; and determining means responsive to said sample level and a predetermined one of said actual sample levels for determining whether an actual sample of said burst signal is produced at said 
     
     
        predetermined phase angle. .Iaddend. .Iadd.52.  Apparatus as set forth in claim 17 which further includes: means for storing reference samples of color burst cycles of a horizontal line of the television signal generated by said sampling means and clocked by a phase stable clock signal and for generating said output clock signal phase synchronized with said reference samples. .Iaddend. .Iadd.53. Apparatus as set forth in claim 52 wherein:   said means for generating comparison samples stores sets of comparison samples of color burst cycles from subsequent horizontal lines; and   said detecting means detects a change between the phase of each set of stored comparison samples and the phase of the reference samples. .Iaddend. .Iadd.54. An apparatus as set forth in claim 25 which further includes:   means for storing reference samples of said synchronizing component generated by said sampling means clocked by a phase stable clock signal and for generating said output clock signal phase synchronized with said reference samples. .Iaddend. .Iadd.55. An apparatus as set forth in claim 54 wherein:   said means for generating comparison samples stores sets of comparison samples of said synchronizing component; and   said detecting means detects a change between the phase of the comparison samples and the phase of the reference samples. .Iaddend. .Iadd.56. A method of controlling the phase of a clock signal which effects sampling of a color television signal having a color burst signal, the clock signal having a desired sampling phase relative to the color burst signal, said method comprising the steps of:   sampling a plurality of values of the color burst signal at the actual phase of the sampling clock relative to the color burst signal;   generating an error signal as a function of a plurality of said sampled values which is indicative of a difference between the actual sampling phase and the desired sampling phase; and   adjusting the phase of the clock signal in response to said error signal to   
     
     
        eliminate the phase difference. .Iaddend. .Iadd.57.  A method as set forth in claim 56 wherein the step of adjusting the phase of the clock signal includes the step of: adjusting the phase of the clock signal in response to said error signal to eliminate the phase difference when the error signal is within a selected range; and   rephasing the clock signal such that it is phase synchronized with a reference when the error signal is outside of said selected range. .Iaddend. .Iadd.58. A method of sampling a color television signal having a color burst signal which obtains sample values of the color television signal relative to a selected phase of the color burst signal, the sampling of the color television signal producing sample values which are a function of the actual sampling phase of a sampling clock signal relative to the color burst signal, the sampling clock signal having a desired sampling phase producing the sample values of the color television signal at the selected phase, said method comprising the steps of:   generating the sampling clock signal with a controllable phase;   separating samples of the color burst signal from the samples of the color television signal to obtain sample values thereof which are determined by the actual sampling phase of the sampling clock;   determining, from a plurality of sample values of the color burst signal, the actual sampling phase of the sampling clock signal; and   controlling the phase of the sampling clock signal in accordance with the determined sampling phase to adjust the sampling phase to the desired   
     
     
        sampling phase. .Iaddend. .Iadd.59.  The method as set forth in claim 58 further comprising the steps of: converting each obtained sample value to a digital representation prior to the step of determining the sampling phase. .Iaddend. .Iadd.60. The method of claim 58 wherein the step of controlling the phase of the sampling clock signal includes the steps of:   controlling the phase of the sampling clock signal in accordance with the determined sampling phase to adjust the sampling phase to the desired sampling phase when the difference between the determined sampling phase and the desired sampling phase is within a selected range; and   rephasing the sampling clock signal such that it is phase synchronized to a reference when the difference between the determined sampling phase and the desired sampling phase is outside of said selected range. .Iaddend. .Iadd.61. A method for sampling an analog signal having a reference signal component by controlling the phase of a sampling clock signal to a desired sampling phase relative to the reference signal component, said method comprising:   sampling the reference signal with the sampling clock to produce sample values thereof;   determining from the sample values of said reference signal the actual phase relation between said sampling clock signal and the reference signal component;   determining from the sample values of said reference signal the desired phase relation between said sampling clock signal and the reference signal component;   generating an error signal indicative of a difference between said actual sampling phase and said desired sampling phase; and   adjusting the phase of said sampling clock signal in accordance with the error signal to eliminate the difference between the actual phase and the   
     
     
        desired phase. .Iaddend. .Iadd.62.  A method as set forth in claim 61 wherein the sampled signal is a composite television signal and the reference signal component is the color burst synchronizing signal of the composite signal. .Iaddend. .Iadd.63. A method as set forth in claim 61 which further includes the step of: converting the sampled analog signal into digital values at times based upon the sampling clock. .Iaddend. .Iadd.64. A method as set forth in claim 63 wherein said step of determining the actual phase includes the step of:   utilizing one of said sampled reference signal values as an indication of the actual phase relation between said sampling clock signal and said reference signal. .Iaddend. .Iadd.65. A method as set forth in claim 64 wherein said step of determining the desired phase includes the step of:   utilizing at least one other of said sampled reference signal values to calculate a value for said one reference sample value which is an indication of the desired phase relation between said sampling clock signal and said reference signal. .Iaddend. .Iadd.66. A method as set forth in claim 65 wherein said step of generating said error signal includes the step of:   differentially combining said actual phase indication value and said desired phase indication value. .Iaddend.