Reduced rate sampling process in pulse code modulation of analog signals

Claim 2

A TV communications system for digitizing and communicating an analog TV composite signal comprising: a. transmitter comb filter means responsive to a composite TV signal having modulated chrominance components interleaved with luminance components for separating said modulated chrominance from said luminance, said comb filter comprising; i. first means for combing over the entire band of said composite signal for extracting said modulated chrominance components from said composite signal; ii. band pass filter means responsive to said extracted modulated chrominance signal for blocking all signals below a certain frequency and for passing said modulated chrominance, said certain frequency being the frequency just below the lowest sideband of said modulated chrominance; and iii. means for subtracting said band passed chrominance from said composite signal to obtain a luminance signal which is uncombed up to said certain frequency and which has the modulated chrominance combed therefrom; b. means for pulse amplitude sampling said latter luminance at a sampling rate fy, where fy - Wy is substantially equal to or less than the said certain frequency and is an odd multiple of half the TV horizontal line rate and is less than 2 Wy, and wy the upper frequency of the luminance signal bandwidth; and c. means for converting each sample pulse amplitude into a digital quantity.

Claim 3

A system as claimed in claim 1, further comprising, a. means for reconverting said digital quantities into an analog signal, said analog signal representing said luminance component with Sampling energy interleaved down to a frequency of fy - Wy, b. a luminance channel comb filter means responsive to said last-mentioned analog signal for combing said sampling energy out of said analog signal, said comb filter means comprising, i. first means for combing over the entire band of said analog signal for extracting the sampling energy, ii. band pass filter means responsive to said extracted sampling energy for blocking all frequencies up to fy - Wy and for passing all frequencies between fy - Wy and Wy of said extracted signal, and iii. means for subtracting said band passed sampling energy from said analog signal to obtain a luminance signal which is uncombed below fy - Wy and which has the interleaved sampling energy combed therefrom.

Claim 4

A system as claimed in claim 1, wherein said band pass filter of said transmitter comb filter has an amplitude characteristic which is substantially zero up to said certain frequency and which rises rapidly to a fixed amplitude at said certain frequency and remains substantially constant within 3 db of said fixed amplitude from said certain frequency to Wy.

Claim 5

A system as claimed in claim 1, wherein said band pass filter of said transmitter comb filter includes a phase equalizer for providing said band pass filter with a linear phase shift characteristic that matches the linear phase shift characteristic of a conventional delay line.

Claim 6

A system as claimed in claim 4, wherein said means for subtracting comprises means for delaying said uncombed composite signal an amount which equals the inherent delay caused by said band pass filter.

Claim 7

A system as claimed in claim 5, wherein said first means of said transmitter comb filter comprises, a. means for delaying said composite signal an amount equal to twice the horizontal line period of said composite signal, b. means for delaying said composite signal an amount equal to the horizontal line period of said composite signal, c. means for adding the signal delayed by two horizontal line periods with the composite signal undelayed to form a sum signal, and d. means for subtracting said sum signal from the composite signal delayed by one horizontal line period.

Claim 8

A TV communications system for digitizing and communicating a TV signal having at least a luminance component, comprising, means for sampling said luminance component at a frequency fy which is less than 2 Wy, where fy is an odd multiple of half the horizontal line rate of the TV signal and where Wy is the upper frequency of said luminance component, means for digitizing said samples, means for reconverting said digitized samples into an analog signal representing said luminance component with sampling energy being interleaved at odd multiples of the horizontal line frequency down to fy - Wy, and luminance channel comb filter means having a pass band from zero to fy - Wy and alternate pass and stop bands from fy - Wy to Wy, said pass bands centered at the harmonics of the horizontal line frequency and said stop bands centered at odd multiples of half the horizontal line frequency, wherein said luminance channel comb filter comprises, a. first means for combing over the entire band Wy of said analog signal, said first means having a transfer characteristic with alternate stop and pass bands, said pass bands being centered at frequencies equal to odd multiples of half the horizontal line rate of said TV signal, and said stop bands being centered at frequencies which are the harmonics of said horizontal line frequency, b. band phase filter and phase equalizing means for passing a portion of the output of said first means, said filter and equalizer having a phase shift transfer characteristic which is linear and which matches a conventional delay line and having an amplitude transfer characteristic which is substantially zero up to fy - Wy and is substantially constant from fy - Wy up to Wy, c. means for delaying the uncombed analog signal an amount equal to the inherent delay of said band pass filter and phase equalizer, and d. subtraction means for subtracting the output of said band pass filter and phase equalizer from the output of said delaying means.

Claim 9

A TV communications system for digitizing and communicating a TV signal having at least a luminance component, comprising, means for sampling said luminance component at a frequency fy which is less than 2 Wy, where fy is an odd multiple of half the horizontal line rate of the TV signal and where Wy is the upper frequency of said luminance component, means for digitizing said samples, means for reconverting said digitized samples into an analog signal representing said luminance component with sampling energy being interleaved at odd multiples of the horizontal line frequency down to fy - Wy, and luminance channel comb filter means having a pass band from zero to fy - Wy and alternate pass and stop bands from fy - Wy to Wy, said pass bands centered at the harmonics of the horizontal line frequency and said stop bands centered at odd multiples of half the horizontal line frequency, wherein said luminance channel comb filter comprises, a. first means for combing over the entire band Wy of said analog signal, said first means having a transfer characteristic with alternate stop and pass bands, said pass bands being centered at frequencies equal to odd multiples of half the horizontal line rate of said TV signal, and said stop bands being centered at frequencies which are the harmonics of said horizontal line frequency, b. band phase filter and phase equalizing means for passing a portion of the output of said first means, said filter and equalizer having a phase shift transfer characteristic which is linear and which matches a conventional delay line and having an amplitude transfer characteristic which is substantially zero up to fy - Wy and is substantially constant from fy - Wy up to Wy, c. means for delaying the uncombed analog signal an amount equal to the inherent delay of said band pass filter and phase equalizer, and d. subtraction means for subtracting the output of said band pass filter and phase equalizer from the output of said delaying means.

Claim 10

A system as claimed in claim 7, wherein said TV signal also comprises chrominance components I and Q having respective bandwidths Wi and Wq, said system further comprising; a. means for sampling said chrominance component I at a frequency fi where fi is less than 2 Wi and is an odd multiple of half the horizontal line rate of said TV signal, b. means for digitizing said samples of said I component, c. means for reconverting said last mentioned digitized sampler into an I component analog signal representing said I component with sampling energy being interleaved at odd multiples of the horizontal line frequency down to fi - Wi, and d. I channel comb filter means having a pass band from zero to fi - Wi and alternate pass and stop bands from fi - Wi to Wi, said pass bands being centered at the harmonics of said horizontal line frequency and said stop bands being centered at odd multiples of half the horizontal line frequency, e. means for sampling said chrominance component Q at a frequency fq where fq is less than 2 Wq and is an odd multiple of half the horizontal line rate of said TV signal, f. means for digitizing said sampler of said Q component, g. means for reconverting said last mentioned digitized sampler into a Q component analog signal representing said Q component with sampling energy being interleaved at odd multiples of the horizontal line frequency down to fq - Wq, and h. Q channel comb filter means having a pass band from zero to fq - Wq and alternate pass and stop bands from fq - Wq to Wq, said pass bands being centered at the harmonics of said horizontal line frequency and said stop bands being centered at odd multiples of half the horizontal line frequency.

Claim 11

A system as claimed in claim 8, wherein said I channel and Q channel comb filters are the same as said luminance channel comb filter with the exception that, a. the respective first means comb over the bands Wi and Wq, respectively, and b. the respective band pass filters and phase equalizers have zero amplitude transfer characteristics up to fi - Wi and fq -Wq, respectively, and have stop and pass bands from fi - Wi to Wi and from fq - Wq to Wq, respectively.