Preliminary

AS2520/21/20B/21B

Rev. 5.1

Page 1

May 1999

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

Typical Application

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 ensure acoustic stability.

Package

Available in 28 pin SOP and DIP.

Lb

3V

La

AS2520

DIALLER

µCONTROLLER

LCD DRIVER

1

2

3

4

5

6

7

8

9

*

0

#

HSM

HFM

TELEPHONE

SPEECH CIRCUIT

WITH

LOUDHEARING,

HANDSFREE,

DC/DC CONVERTER

Figure 1: Typical Handsfree Telephone Application

Austria Mikro Systeme International AG

Telephone Speech Circuit

with Loudhearing and Handsfree