Carrier phase and sampling time recovery in modulation systems

Claim 2

A sampling system for sampling signal data including a sample time adjusting means for adjusting the time for sampling said signal data comprising: system input means including demodulation means for demodulating a carrier signal containing said signal data and first sampling means for sampling said signal data in accordance with said sample time adjusting means; equalizer means coupled to said sampling means for reducing effects of distortion on said signal data; differentiator means coupled to said system input means for differentiating said signal data; combining means having a first input circuit means coupled to the output of said equalizer means and having a second input circuit means coupled to the output of said differentiator means to thereby produce a control signal, said first input means including threshold detection means the output of which provides system output indications of said signal data and said second input circuit means including a second sampling means for sampling the differentiated signal data in accordance with said sampled time adjusting means; and means coupling said control signal to said sample time adjusting means to control the sample time of said first and second sampling means.

Claim 3

The sampling circuit as set forth in claim 1 wherein said equalizer means includes an adaptive equalizer means.

Claim 6

The method as set forth in claim 3 comprising the further steps of: differentiating said first low-pass signal and sampling the differentiated signal thereof; and further combining the said sampled values of said low-pass signal with the sampled values of said differentiated signal to thereby provide an output signal indicative of the difference in time between the sampling time used and an optimum sampling time.

Claim 7

The method as set forth in claim 4 comprising the further step of equalizing the said sampled values of said first low-pass signal before combining with the respective said sampled values of said second low-pass signal and the said sampled values of said differentiated signal.

Claim 8

The method as set forth in claim 5 comprising the further steps of feeding back the said output signal indicative of the phase difference to adjust the phase of said inphase signal to that of said carrier phase and feeding back the said output signal indicative of the difference in time to adjust the sampling time used to that of said optimum sampling time.

Claim 9

The method as set forth in claim 6 wherein the step of combining and the step of further combining the said sampled values each involve combining the said sampled values to form a product.

Claim 10

A demodulation system including carrier phase recovery means for recovering the phase of a received modulated carrier comprising: demodulation means including local oscillator means for producing a demodulating signal and first and second demodulator means coupled to receive said modulated carrier signal, said first demodulator means coupled to said local oscillator means for receiving said demodulating signal therefrom to provide an inphase demodulator channel means and said second demodulator means coupled to said local oscillator means for receiving said demodulating signal therefrom to provide a quadrature demodulator channel means; sampling means coupled to said demodulation means for sampling the demodulated signals from each of said inphase demodulator channel means and said quadrature demodulator channel means; means including combining means and first and second coupling means to said sampling means to combine the sampled signal from said inphase demodulator channel means with the sampled signal from said quadrature demodulator channel means to thereby provide an output signal indicative of the difference in phase between said modulated carrier signal and said demodulating signal from said local oscillator means; and feedback control circuit means coupling said output signal from said combining means to said local oscillator means to thereby adjust the phase of said oscillator means in accordance with the said output signal on said combining means whereby an iterative and sequential feedback control operation act to recover said carrier phase.

Claim 11

A demodulation system including carrier phase recovery means for recovering the phase of a received modulated carrier comprising: demodulation means including local oscillator means for producing a demodulating signal and first and second demodulator means coupled to receive said modulated carrier signal, said first demodulator means coupled to said local oscillator means for receiving said demodulating signal therefrom to provide an inphase demodulator channel means and said second demodulator means coupled to said local oscillator means for receiving said demodulating signal therefrom to provide a quadrature demodulator channel means; sampling means coupled to said demodulation means for sampling the demodulated signals from each of said inphase demodulator channel means and said quadrature demodulator channel means; means including combining means and first and second coupling means to said sampling means to combine the sampled signal from said inphase demodulator channel means with the sampled signal from said quadrature demodulator channel means to thereby provide an output signal indicative of the difference in phase between said modulated carrier signal and said demodulating signal from said local oscillator means; and feedback control circuit means coupling said output signal from said combining means to said local oscillator means to thereby adjust the phase of said oscillator means in accordance with the said output signal on said combining means whereby an iterative and sequential feedback control operation act to recover said carrier phase.

Claim 12

The system as set forth in claim 8 wherein said first coupling means includes equalizer means, said equalizer means providing an output to be used as both a demodulation system output and an output to be applied to said combining means.

Claim 13

The system as set forth in claim 9 further including; differentiator means having input means and output means with the input means coupled to receive the demodulated signal from said inphase demodulator channel means; further sampling means coupled to sample the output from said output means of said differentiator means; sample time adjusting means coupled to both said sampling means and to said further sampling means to adjust the sampling time of each in accordance with the input signal applied to said sample time adjusting means; further means including further combining means and further first and second coupling means coupling said combining means respectively to the said output means of said differentiator means and to the said output of said equalizer means to thereby provide an output signal indicative of the amount of error between the operating sampling time and the optimum sampling time; and further feedback control circuit means coupling the said output signal of said further combining means to the input of said sample time adjusting means to thereby adjust the sampling time of both said sampling means and said further sampling means in accordance with the said output signal on said further combining means whereby an iterative and sequential feedback control operation acts to provide optimum sampling time.

Claim 14

The system as set forth in claim 10 wherein said equalizer means are adaptive and wherein said first coupling means further includes threshold detection means coupled to the output of said equalizer means, said threshold detection means providing an output to be used as both a demodulation system output and an output to be applied to both said combining means and said further combining means.

Claim 15

The system as set forth in claim 11 wherein said feedback control circuit means and said further feedback control circuit means each include integration means.

Claim 16

The system as set forth in claim 12 wherein said inphase demodulator channel means and said quadrature demodulator channel means each include low-pass filter means coupled to provide demodulated signals to said sampling means.

Claim 17

In a data communications system a coherent demodulator circuit for demodulating the vestigal sideband of a linearly modulated carrier signal used to frequency translate a PAM baseband signal to passband, said demodulator circuit including both oscillator means producing a demodulating signal and coupled to provide an inphase demodulator channel and a quadrature demodulator channel and carrier phase recovery means coupled to the outputs thereof, said carrier phase recovery means comprising: sampling means coupled to sample the signal output from both said inphase demodulator channel and from said quadrature demodulator channel; threshold detection means having an input and an output with said input coupled to said sampling means to receive the sampled signal output from said inphase demodulator channel; and combining means coupled to combine said output from said threshold detection means with the sampled signal output from said quadrature demodulator channel to produce a control voltage indicative of the difference between the phase of said carrier signal and the phase of the said demodulating signal of said oscillator means.

Claim 18

In a data communications system a coherent demodulator circuit for demodulating the vestigal sideband of a linearly modulated carrier signal used to frequency translate a PAM baseband signal to passband, said demodulator circuit including both oscillator means producing a demodulating signal and coupled to provide an inphase demodulator channel and a quadrature demodulator channel and carrier phase recovery means coupled to the outputs thereof, said carrier phase recovery means comprising: sampling means coupled to sample the signal output from both said inphase demodulator channel and from said quadrature demodulator channel; threshold detection means having an input and an output with said input coupled to said sampling means to receive the sampled signal output from said inphase demodulator channel; and combining means coupled to combine said output from said threshold detection means with the sampled signal output from said quadrature demodulator channel to produce a control voltage indicative of the difference between the phase of said carrier signal and the phase of the said demodulating signal of said oscillator means.

Claim 19

The demodulator circuit as set forth in claim 14 further including sample time recovery means, said sample time recovery means comprising: differentiation means coupled to said inphase demodulator channel to provide a differentiated output; and further combining means coupled to combine the said differentiated output from said differentiation means with the said output from said threshold detection means to produce a further control voltage indicative of the difference between the sampling time of said sampling means and an optimum sampling time.

Claim 20

The demodulator circuit as set forth in claim 15 wherein said control voltage and said further control voltage are each fed back to respectively adjust the phase of said demodulating signal to carrier phase and the sampling time of said sampling means to optimum sampling time.

Claim 21

A demodulation system including carrier phase recovery means for recovering the phase of a received modulated carrier signal comprising: demodulation means including phase-adjustable local oscillator means and first and second demodulator means coupled to receive said modulated carrier, said first and second demodulator means coupled to said local oscillator means so as to form an inphase demodulator channel and a quadrature demodulator channel; equalizer means having an input and an output with the input coupled to receive the demodulated output signal from said inphase demodulator channel; first sampling means coupled to sample the said output from said equalizer means and second sampling means coupled to sampLe the demodulated output from said quadrature demodulator channel; means including combining means coupled to said first and second sampling means to combine the sampled output from said equalizer means with the sampled output from said quadrature channel to provide an output signal indicative of estimates of the amount of phase error between said received carrier signal and said local oscillator means; and feedback control circuit means coupled to said combining means and to said local oscillator means to adjust the phase of said local oscillator means in accordance with the said output signal indicative of estimates of the amount of phase error from said combining means.

Claim 22

A demodulation system including carrier phase recovery means for recovering the phase of a received modulated carrier signal comprising: demodulation means including phase-adjustable local oscillator means and first and second demodulator means coupled to receive said modulated carrier, said first and second demodulator means coupled to said local oscillator means so as to form an inphase demodulator channel and a quadrature demodulator channel; equalizer means having an input and an output with the input coupled to receive the demodulated output signal from said inphase demodulator channel; first sampling means coupled to sample the said output from said equalizer means and second sampling means coupled to sampLe the demodulated output from said quadrature demodulator channel; means including combining means coupled to said first and second sampling means to combine the sampled output from said equalizer means with the sampled output from said quadrature channel to provide an output signal indicative of estimates of the amount of phase error between said received carrier signal and said local oscillator means; and feedback control circuit means coupled to said combining means and to said local oscillator means to adjust the phase of said local oscillator means in accordance with the said output signal indicative of estimates of the amount of phase error from said combining means.

Claim 23

The system as set forth in claim 17 wherein threshold detection means coupled between said first sampling means and said combining means to provide a detected sample of the said output of said equalizer means for said combining means.

Claim 24

The system as set forth in claim 18 wherein the said means including also includes integration means coupling said combining means to said feedback control circuit means.

Claim 25

The system as set forth in claim 19 further including: differentiator means having an input and an output with said input coupled to the said output of said equalizer means; third sampling means coupled to sample the said output of said differentiator means; sample time adjusting means coupled to said first, second and third sampling means to adjust the sampling time thereof; further means including further combining means coupled to combine the said output from said differentiator means with the said detected sample from said threshold detection means to provide an output signal indicative of an estimate of the amount of sampling time error between the operating sampling time and optimum sampling time; and further feedback control circuit means coupled to said further combining means and to said sample time adjusting means to adjust the sample time in accordance with the said output signal indicative of an estimate of the amount of sampling time error from said further combining means.

Claim 26

The system as set forth in claim 20 wherein the said further means including also includes integration means coupling said further combining means to said further feedback control circuit means.

Claim 27

The system as set forth in claim 21 wherein said combining means and said further combining means each include multiplication means.

Claim 28

A demodulation system including oscillator means coupled to form an inphase demodulator channel and a quadrature demodulator channel and further including carrier phase and sample time recovery means for recovering carrier phase and sample time from a received modulated signal, said carrier phase and sample time recovery means comprising: differentiation means coupled to said inphase demodulator channel to provide a differentiated demodulated signal therefrom; sampling means coupled to said inphase demodulator channel, said quadrature demodulator channel and said differentiation means to provide respective sampled signals therefrom; sample time adjustment means coupled to said sampling means to adjust the sample time of said sampling means; equalizer means having an input and an output with said input coupled to receive the said sampled signals from said inphase demodulator channel; combining means coupled to combine the said output from said equalizer means respectively with the said sampled signals from said quadrature demodulator channel to produce a first error signal indicative of the difference inphase between said received carrier signal and said oscillator means and with said sampled signals from said differentiation means to produce a second error signal indicative of the difference between the operating sample time and optimum sampling time; first feedback control circuit means coupling said first error signal to said oscillator means to adjust the phase of said oscillator mEans in accordance with said first error signal; and second feedback control circuit means coupling said second error signal to said sample time adjustment means to adjust the sample time of said sampling means in accordance with said second error signal.

Claim 29

A demodulation system including oscillator means coupled to form an inphase demodulator channel and a quadrature demodulator channel and further including carrier phase and sample time recovery means for recovering carrier phase and sample time from a received modulated signal, said carrier phase and sample time recovery means comprising: differentiation means coupled to said inphase demodulator channel to provide a differentiated demodulated signal therefrom; sampling means coupled to said inphase demodulator channel, said quadrature demodulator channel and said differentiation means to provide respective sampled signals therefrom; sample time adjustment means coupled to said sampling means to adjust the sample time of said sampling means; equalizer means having an input and an output with said input coupled to receive the said sampled signals from said inphase demodulator channel; combining means coupled to combine the said output from said equalizer means respectively with the said sampled signals from said quadrature demodulator channel to produce a first error signal indicative of the difference inphase between said received carrier signal and said oscillator means and with said sampled signals from said differentiation means to produce a second error signal indicative of the difference between the operating sample time and optimum sampling time; first feedback control circuit means coupling said first error signal to said oscillator means to adjust the phase of said oscillator mEans in accordance with said first error signal; and second feedback control circuit means coupling said second error signal to said sample time adjustment means to adjust the sample time of said sampling means in accordance with said second error signal.

Claim 30

The system as set forth in claim 23 wherein said first and second feedback control circuit means each include integration means.

Claim 31

The system as set forth in claim 24 wherein said received modulated signal comprises a vestigal sideband of a carrier used to modulate a pulse amplitude modulation signal from baseband to passband.

Claim 32

The system as set forth in claim 25 wherein said inphase demodulator channel and said quadrature demodulator channel each include low-pass filter means.