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ST5080

PIAFE PROGRAMMABLE ISDN AUDIO FRONT END

STMicroelectronics 

ST5080A

GENERAL DESCRIPTION

ST5080A PIAFE is a combined PCM CODEC/FIL-

TER device optimized for ISDN Terminals and Digi-

tal Telephone applications. This device is A-law

and Mu-law selectable and offers a number of pro-

grammable functions accessed through a serial

control channel.

Depending on mode selected, channel control is

provided by means of a separate serial channel

control MICROWIRE compatible or multiplexed

with the PCM voice data channel in a GCI com-

patible format requiring only 4 digital interface

pins. When separate serial control interface is se-

lected, PCM interface is compatible with Combo I

and Combo II families of devices such as

ETC5057/54, TS5070/71.

PIAFE is built using SGS-THOMSON’s advanced

HCMOS process.

Transmit section of PIAFE consists of an amplifier

with switchable high impedance inputs followed

by a programmable gain amplifier, an active RC

antialiasing pre-filter to provide attenuationof high

frequency noise, an 8th order switched capacitor

band pass transmit filter and an A-law/Mu-law se-

lectable compandig encoder.

Receive section consist of an A-law/Mu-law se-

lectable expanding decoder which reconstructs

the analog sampled data signal, a 3400 Hz low

pass filter with sin X/X correction followed by two

separate programmable attenuation blocks and

two power amplifiers: One can be used to drive

an earpiece, and the other to drive a 50 Ω loud-

speaker.

Programmable functions on PIAFE include a

Ring/Tone generator which provides one or two

tones and can be directed to earpiece or to loud-

speaker or alternatively a piezo transducer up to

600nF.

A separate programmable gain amplifier allows

gain control of the signal injected. Ring/Tone gen-

erator provides sinewave or squarewave signal

with precise frequencies which may be also di-

rected to the input of the Transmit amplifier for

DTMF tone generation.

An auxiliary analog input (EAIN) is also provided

to enable for example the output of an external

band limited Ring signal to the Loudspeaker.

Transmit signal may be fed back into the receive

ampifier with a programmable attenuation to pro-

vide a sidetone circuitry.

A switchable anti-accoustic feed-back system

cancels the larsen effect in speech monitoring ap-

plication.

Two additional pins are provided for insertion of

an external Handfree function in the Loudspeaker

receive path.

An output latch controlled by register program-

ming permits external device control.

PIN FUNCTIONS

Pin

1,2

Name

HFI, HFO

3,4

VFr+, VFr–

5

VCC

6,7

LS-,LS+

Description

Hands free I/Os:

These two pins can be used to insert an external Handfree

circuit such as the TEA 7540 in the receive path. HFO is an

output which provides the signal issued from output of the

receive low pass filter while HFI is a high impendance input

which is connected directly to one of the inputs of the

Loudspeaker amplifier.

Receive analog earpiece amplifier complementary outputs,

capable of driving load impedances between 100 and 400 Ω or

a piezo up to 150nF. These outputs can drive directly earpiece

transductor. The signal at this output can drive be the summ of:

- Receive Speech signal from DR,

- Internal Tone Generator,

- Sidetone signal.

Positive power supply input for the digital section.

+5 V + 10%.

Receive analog loudspeaker amplifier complementary outputs,

intended for driving a Loudspeaker: 80 mW on 50Ω load

impedance can be provided at low distorsion meeting

specifications.

Alternatively this stage can drive a piezo transducer up to

600nF. The signal at these outputs can be the sum of:

- Receive Speech signal from DR,

- Internal Tone generator,

- External input signal from EAIN input.

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