A first CMOS chip, containing line interface/speech, power extraction, loudhearing, handsfree, DC/DC converter and ringer amplifier in a 28 pin package powered only from the line, is presented. The chip provides an enhanced anti-Larsen circuit to prevent acoustic howling in loudhearing mode and a revolutionary "handsfree mode" voice control system which is virtually independent of any background noise and works in a dynamic half duplex as close to full duplex as the acoustic loop gain allows. This paper describes the architectural features of the system and the design of the main building blocks of the integrated circuit. >
['K. Hayat-Dawoodi', 'Oluf Alminde', 'V. Kunc', 'Manfred Pauritsch']
A universal telephone audio circuit with loudhearing and handsfree operation in CMOS technology