MM74HC943 300 Baud Modem General Description The MM74HC943 is a full duplex low speed modem. It provides a 300 baud bidirectional serial interface for data communication over telephone lines and other narrow bandwidth channels. It is Bell 103 compatible. The MM74HC943 utilizes advanced silicon-gate CMOS technology. Switched capacitor techniques are used to peform analog signal processing. MODULATOR SECTION The modulator contains a frequency synthesizer and a sine wave synthesizer. It produces a phase coherent frequency shift keyed (FSK) output. LINE DRIVER AND HYBRID SECTION The line driver and hybrid are designed to facilitate connection to a 600X phone line. They can perform two to four wire conversion and drive the line at a maximum of b9 dBm. DEMODULATOR SECTION The demodulator incorporates anti-aliasing filters, a receive filter, limiter, discriminator, and carrier detect circuit. The nine-pole receive filter provides 60 dB of transmitted tone rejection. The discriminator is fully balanced for stable operation.