Method of 90 degree phase-shift modulation and demodulation usin

Details Method of 90 degree phase-shift modulation and demodulation usin Method of 90 degree phase-shift modulation and demodulation usin

1990-07-06

1992-03-03

Kostak, Victor R.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358 23, H04N 708

Patent

active

050937235

ABSTRACT:
A method for 90.degree. phase-shift modulation and demodulation in a circuit having a PLL. A phase-shift of 90.degree. between a main and an additional signal is provided. The method comprises the steps of: modulating by (a) selecting a specified position and inserting a pilot signal, (b) giving the phase-shift of 90.degree. to an image carrier wave and (c) generating a modulated signal; and demodulating by (d) receiving the modulated signal and demodulating the main and additional signals having phase-shift of 90.degree. to each other, (e) generating a frequency locked to the transmitted signal and controlling an output of a voltage controlled oscillator and reproducing the main and additional signals of step (d). By inserting the pilot signal into the overscanned interval of the horizontal line of the standard image signal and using it again as the reference signal of the remote PLL, the phase of the image carrier waves between the transmitter and receiver are locked to the same reference, so that phase error due to the 90.degree. phase-shift modulation and demodulation is removed and the signal attenuation and crosstalk are prevented.

REFERENCES:
patent: 3609223 (1971-09-01), Tajiri et al.
patent: 4626928 (1986-12-01), Nagano
patent: 4668997 (1987-05-01), Nagano et al.
patent: 4799102 (1989-01-01), Kobayashi
patent: 4947241 (1990-08-01), Basile et al.

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