Data Modems with Integrated Digital Filters and Modulators

The application of a binary transversal filter as transmitting filter and a digital circuit as modulator makes it possible to construct data transmitters consisting only of transistors and resistors. The modulation distortion, caused by the keying of a low-frequency square-wave carrier, can be compensated by a modification of the transfer function of the transmitting filter, provided the carder frequency is chosen to be a multiple of half the bit rate. This principle makes it possible to realize the whole data transmitter in one single integrated circuit. The binary transversal filter, provided with an analog-to-digital converter, can also be used to construct the data receiver for the greater part with digital circuitry.