Modulators – Amplitude modulator – Nonlinear device controlled by modulating signal
Patent
1986-04-07
1987-08-11
Laroche, Eugene R.
Modulators
Amplitude modulator
Nonlinear device controlled by modulating signal
375 62, 455 93, H03C 300
Patent
active
046864903
ABSTRACT:
A digital modulator for selectably generating differential phase shift keyed (PSK) data signals and frequency shift keyed (FSK) data signals is disclosed. A clock generator (10) provides carrier frequency clock signals and a plurality of phase-shifted high frequency clock signals. A CLX generator (11) selects the proper PSK or FSK carrier clock. A data scrambler (17) accepts a serial data input stream and provides the scrambled dibit to the dibit encoder (12). The dibit encoder (12) converts the scrambled dibit into two phase-shifting control signals. A three-tap finite impulse response filter (13) generates carrier phase signals by splitting each cycle of the selected carrier clock into eight phases, and, for PSK operation, provides phase shifting in response to the two phase-shifting control signals. A multiplexer (14) selects one of the phase-shifter high frequency clocks in response to the carrier phase signals. A signal selector (15) converts the selected phase-shifted high frequency clock signal into a pulsewidth-modulated clock signal. The signal filter (16) provides the PSK/FSK data signal by integrating the pulsewidth-modulated clock signal and also provides band pass filtering to clean up the waveform. The result is a selected PSK/FSK data signal with low distortion, reduced transient DC, and decreased sensitivity to temperature and component selection since bit weighting resistors are not required to generate the output waveform. Also disclosed is a versatile digital-to-analog converter/data modulator for generating FSK and PSK data signals, guard tones, answer tones, dual-tone multiple-frequency dialing signals, and a method for generating frequency-modulated signals.
REFERENCES:
patent: 4058772 (1977-11-01), Mogi et al.
patent: 4370747 (1983-01-01), Bugg et al.
Hayes Microcomputer Products, Inc.
LaRoche Eugene R.
Pascal Robert J.
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