Receiver for phase-shift modulated carrier signals
First Claim
1. A receiver for recovering digital data modulated upon a carrier waveform in a digital communications system, comprising:
- means for receiving said carrier modulated by daid digital data;
means for band-pass filtering the received modulated carrier;
loop means receiving the band-pass filtered modulated carrier for providing a loop signal having a frequency essentially locked to the frequency of the received modulated carrier;
means for mixing said loop signal with the bandpass-filtered modulated carrier to form a output signal responsive to the phase difference therebetween;
means for low-pass filtering said mixing means output signal to recover the digital data from said modulated carrer;
means receiving the low-pass-filtered output signal for recovering a baud synchronization signal therefrom, and including means for providing a pulse at each transition at the recovered digital data waveform received from said low-pass filtering means;
means for providing a local clock waveform at first and second frequencies respectively greater than and less than the nominal frequency of the transitions of the recovered digital data waveform;
means for detecting the magnitude of the timing difference between said transition pulses and the transitions of said local clock waveform; and
means for controlling the percentage of time during which each of said first and second frequencies is provided by said local clock waveform providing means responsive to the dectected transition timing difference information, to cause the local clock and digital data waveform transitions to occur essentially simultaneously;
said local clock waveform being the local baud synchronizing signal.
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Accused Products
Abstract
A receiver for recovering digital data from a phase-shift-modulated carrier in a data communications system, utilizes a relatively wide band-pass filter providing the received modulated signal to a pair of phase-locked loops. The first phase-locked loop provides a local oscillator signal tracking the exact frequency and phase of the received signal, which is itself locked to a multiple of a system-wide frequency. The second phase-locked loop acts as a synchronous data detector. Inversion circuitry, in the first phase lock loop, is controlled by the detected data output from the second phase-lock loop, for preventing the 180° phase modulation from disturbing the frequency-tracking local oscillator phase-lock loop.
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Citations
23 Claims
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1. A receiver for recovering digital data modulated upon a carrier waveform in a digital communications system, comprising:
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means for receiving said carrier modulated by daid digital data; means for band-pass filtering the received modulated carrier; loop means receiving the band-pass filtered modulated carrier for providing a loop signal having a frequency essentially locked to the frequency of the received modulated carrier; means for mixing said loop signal with the bandpass-filtered modulated carrier to form a output signal responsive to the phase difference therebetween; means for low-pass filtering said mixing means output signal to recover the digital data from said modulated carrer; means receiving the low-pass-filtered output signal for recovering a baud synchronization signal therefrom, and including means for providing a pulse at each transition at the recovered digital data waveform received from said low-pass filtering means; means for providing a local clock waveform at first and second frequencies respectively greater than and less than the nominal frequency of the transitions of the recovered digital data waveform; means for detecting the magnitude of the timing difference between said transition pulses and the transitions of said local clock waveform; and means for controlling the percentage of time during which each of said first and second frequencies is provided by said local clock waveform providing means responsive to the dectected transition timing difference information, to cause the local clock and digital data waveform transitions to occur essentially simultaneously;
said local clock waveform being the local baud synchronizing signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification