Abstract: A digital data transmission system for transmitting digital data from digital data handling hardware over a transmission line by analog signal representation and for receiving analog signal representation for reception of digital signals by the digital data handling hardware, incorporates an integrated circuit PSK modem. The modem has a transmitter which includes an encoder for encoding digital data into a first format for conversion to corresponding PSK signals and a transmitter modulator, implemented in switched capacitor circuits, for phase modulating a first carrier frequency according to the first format. The modem has a receiver that includes a demodulator, implemented in switched capacitor circuits, for demodulating PSK signals on a second carrier frequency to provide a second format for conversion to corresponding digital signals, and an encoder for encoding the second format into corresponding digital signals.

Abstract: An integrated circuit FSK transmitter and receiver combination form a modem for receiving and transmitting FSK signals. The FSK transmitter has a square wave generator for providing a clock output at a "mark" frequency or at a "space" frequency within a first frequency band. This clock output is shaped through a band pass filter, shared with the FSK receiver, to provide an FSK output signal which is output through a low pass filter. The input FSK signal is received through a low pass filter and then filtered through the band pass filter. One section of the band pass filter accommodates the clock output while another section accommodates the FSK input. The band pass filter is connected to a demodulating means to provide a filtered sine wave thereto at either a mark or a space frequency within a second frequency band. The demodulating means determines whether the sine wave is at a mark or a space frequency.