Eight channel parallel speech transmission circuit
For the construction of a low priced, high performance communication system, a CMOS mixed analog digital circuit has been developed. The programmable chip contains most of the circuitry required for multichannel speech transmission (50 dB microphone amplifier, eight channel transmitter, eight channel receiver, audio preamplifier). A special combination of single side band modulation and frequency multiplexing is used for the transmission of the speech channels on a single audio line. The eight channels are almost equidistantly located in the low frequency region between 20 kHz and 130 kHz. Clocks for the internal modulators and switched capacitor filters in the transceiver blocks and for an external µController are derived from an integrated oscillator. To reduce power consumption, the chip can be set into standby mode. Only a few additional components are needed to build a multifunctional communication device. The IC has been integrated in a 3 mu m single metal, double poly CMOS proce ss.