Digital signal processing in a LSI 4.8 kbit/s modem

Focusing on a 4.8 Kbit/s modem, the digital signal processing principles used to generate the transmitted signal, to equalize and demodulate the received signal are presented in this paper. They have been selected in order to minimize the amount and speed of computations and to avoid complex arithmetic operations, as divisions for instance. The LSI implementation has been simplified accordingly and carried out with two different approaches followed in the modem transmitter and receiver. In the transmitter, a single dedicated custom LSI integrated circuit is used. In the receiver, the approach is more "general purpose" oriented in order to cover a range of applications broader than strictly the 4.8 Kbit/s modem; it is based on a processor with an arithmetic unit, a sequencer and memories which is implemented by a set of 5 custom LSI circuits. The characteristics of all these custom LSI circuits are presented as well as the technology used.