Abstract: A communications transceiver constructed to minimize the additional external components required for interfacing to the communications medium. The invention includes a communications transceiver with a reduced number of filters comprising a host interface, a control module, a transmit portion and a receive portion. The host interface is coupled to a host computer and functions to exchange transmit, receive and control related data to and from the transceiver. A novel aspect of the invention includes using the same filter for both receiving and transmitting. The single filter plays a dual role, providing filtering function during both receive operation and transmit operation, thus serving to minimize the external components required, the cost of the device and its complexity. A switching device, such as an analog switch, connects the filter either to the output of the transmitter during transmit operation or to the output of the communications medium interface during receive operation.

Abstract: A spread spectrum data communication system utilizing a modulation technique referred to as differential code shift keying (DCSK) transmits data in the form of time shifts between consecutive circularly rotated waveforms of length T known as spreading waveforms. A plurality of bits are transmitted during each symbol period which is divided into a plurality of shift indexes with each shift index representing a particular bit pattern. The spreading waveform is rotated by an amount in accordance with the data to be transmitted or is conveyed in the difference between two consecutive rotations. A correlator employing a matched filter having a template of the chirp waveform pattern is used to detect the amount of rotation of the chirp within the received signal for each symbol. The received data is fed into a shift register and circularly rotated. For each rotation shift, the matched filter generates a correlation sum.