FSK Tone generator circuit

摘要

A tone generator circuit used in a frequency shift keying (FSK) channel in a frequency division multiplexing (FDM) system is disclosed. Each frequency shift between the mark and space tone frequencies is programmed to generate a sequence of discrete intermediate frequencies according to a sinusoidal modulation waveform to produce transmitted tone signals having minimum sideband energy and minimum distortion. A modulation clock generator produces a predetermined number of clock cycles per bit time of the baud rate of the channel. The modulation clock is used to produce a sequence of address signals used to address a PROM containing a set of multiplying code words. Each code word represents a different output tone frequency. The code words are used in a binary rate multipler to multiply a crystal controlled clock signal by the decimal equivalent of the binary code word. The multiplied digital frequency signal is also divided by fixed division factors to produce an output digital tone signal. This digital tone signal is passed through a bandpass filter to remove the sideband noise and thereby produce a sinusoidal output tone signal.