AS2521

Preliminary AS2520/21/20B/21B Telephone Speech Circuit with Loudhearing and Handsfree Austria Mikro Systeme International AG Key Features u Line/speech circuit, loudhearing, handsfree and dc/dc converter on one 28 pin CMOS chip u Operating range from 13 to 100 mA (down to 5 mA with reduced performance) u Soft clipping control eliminating harsh distortion u Volume control of receive signal with squelch and automatic loop gain compensation u Line loss compensation pin selectable u Low noise (max. - 72 dBmp) u Real or complex impedance adjustable u NET 4 compatible u Dynamically controlled voice switching u Same monitor amplifier for loudhearing, handsfree and tone ringer u Very few external components u Power derived from ring signal by switching converter during ringing General Description The AS2520/21/20B/21B are CMOS integrated circuits that contain all the audio functions needed to form a high comfort, line-powered telephone. The devices incorporate line adaptation, speech circuit, loudhearing and handsfree - all supervised by the novel voice and power control circuit. A switching converter is also provided for converting the ring signal. The interface to a dialler/controller is made very simple to allow easy adaptation to a telecom microcontroller. The AS2520 series incorporate volume control for the earpiece and the loudspeaker (AS2520 digital with +/keys and AS2521 analogue with potentiometer). The volume control circuit automatically compensates the loop gain to en...