Pulse or digital communications – Repeaters – Testing
Patent
1991-07-08
1993-02-16
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
332101, H03C 300
Patent
active
051877210
ABSTRACT:
The present invention provides a modulator/generator circuit which includes the following features: a 1200 baud 4-phase differential phase shift keying (DPSK) modulator, a 300 baud frequency shift keying (FSK) modulator, a dual tone multi-frequency (DTMF) generator and 2100/2225 Hz answer tone generators. The DPSK modulator utilizes time-domain filtering techniques. It includes a spectrum controller that shapes the in-band frequency spectrum and attenuates the adjacent channel frequency components to eliminate the conventional requirement of band-pass filters after the modulator. The FSK modulator also utilizes a spectrum controller which, during each data transition, sends out six intermediate frequencies to smooth the frequency changeover. DTMF generation is accomplished by multiplexing two sine-wave counters into a DPSK sinewave look-up ROM. By varying the duty cycle of the multiplexing control signal, the DTMF generator provides a digital pre-emphasis function that boosts the amplitude of the high-band frequencies as referenced to the low-band frequencies. The answer tone section of the circuit is accomplished by sharing portions of the FSK section since the two tones are embedded in the FSK frequencies. A digital DAC is provided for converting the modulated signal (parallel) to a serial bit stream. The modulated signal in analog form is available after a low cost low pass filter.
REFERENCES:
patent: 3890581 (1975-06-01), Stuart
patent: 4748640 (1988-05-01), Staley et al.
patent: 5053728 (1991-10-01), Bogl
National Semiconductor Corporation
Safourek Benedict V.
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