Digital data modulator and digital-to-analog converter

Details Digital data modulator and digital-to-analog converter Digital data modulator and digital-to-analog converter

H - Electricity

03

K

332/34, 354/97

H03K 7/00 (2006.01) H03M 1/00 (2006.01)

Patent

CA 1239450

IMPROVED DIGITAL DATA MODULATOR AND DIGITAL-TO-ANALOG CONVERTER Abstract A digital modulator for selectably generating differential phased 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-shifted 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/FSX 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 tone, answer tone, dual tone mutiple-frequency dialing signal, and a method for generating frequency-modulated signals.

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