A first CMOS chip, containing line interjiace/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-Lursen cixuit to prevent acoustic howling in loudhearing mode arid a revolutionary "handsfree mode '' voice control system which is virtually independent of m y background noise and works in a dynamic half duplex as close to full duplex as the acoustic loop gain allows. This paper describes the axhitectiiral features of the system and the design of the main building blocks of the integrated cixuit.
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