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
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Operating range from 13 to 100 mA (down to 5
mA with reduced performance)
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Soft clipping control eliminating harsh distortion
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Volume control of receive signal with squelch and
automatic loop gain compensation
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Line loss compensation pin selectable
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Low noise (max. - 72 dBmp)
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Real or complex impedance adjustable
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NET 4 compatible
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Dynamically controlled voice switching
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Same monitor amplifier for loudhearing, handsfree
and tone ringer
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Very few external components
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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 ensure acoustic stability.
Typical Application
La
Package
Available in 28 pin SOP and DIP.
Lb
3V
1
4
7
2
5
8
0
3
6
9
#
DIALLER
µCONTROLLER
LCD DRIVER
TELEPHONE
SPEECH CIRCUIT
WITH
LOUDHEARING,
HANDSFREE,
DC/DC CONVERTER
HSM
*
HFM
AS2520
Figure 1: Typical Handsfree Telephone Application
Rev. 5.1
Page 1
May 1999
AMSCO [ AUSTRIAMICROSYSTEMS AG ]
