Phase controlled demodulator for digital communications system

Details Phase controlled demodulator for digital communications system Phase controlled demodulator for digital communications system

1988-06-30

1989-08-01

LaRoche, Eugene R.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

331 4, 331DIG2, H03D 300

Patent

active

048536423

ABSTRACT:
In a phase controlled demodulator, a modulated digital input signal is demodulated into quadrature signals with a carrier recovered by a voltage controlled oscillator. A phase difference between the quadrature signals is detected by a phase detector of Costas loop and applied through a loop filter to the voltage controlled oscillator to control the frequency and phase of the recovered carrier when the frequency deviation between the received and recovered carriers is within a phase control range. When the frequency deviation exceeds the phase control range, the output of the phase detector is a beat of the two carriers and a frequency sweep control voltage is applied to the VCO to search for the missing carrier. The magnitude of the beat is detected and compared with a predetermined threshold value. When the frequency deviation is far beyond the control range, the magnitude of the beat is lower than the threshold, but exceeds it at the instant the demodulator enters the control range, whereupon the frequency sweep control voltage is removed from the VCO.

REFERENCES:
patent: 4423390 (1983-12-01), Waters
patent: 4724401 (1988-02-01), Hogge, Jr. et al.

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