ST5088 datasheet(4/33 Pages) STMICROELECTRONICS

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GENERAL DESCRIPTION

ST5088 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 attenuation of 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 or a piezo transducer up to 600nF.

When the loudspeaker section is set up with

maximum gain (+27dB) the device provide inter-

nally a programmable digital anticlipping system

to avoid output distortion.

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 buzzer).

A simple ringer control interface can bypass

µP

control of sweep frequency and ring ON/OFF

phases.

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

PLCC

Name

Description

1,2

HFI, HFO

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.

3,4

VFr+,VFr–

Receive analog earpiece amplifier complementary

outputs, capable of driving load impedances between 100

and 400

Ω or a piezo ceramic transducer 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.

VCC

Positive power supply input for the digital section. +5 V + 10%.

6,7

LS-,LS+

Receive analog loudspeaker amplifier complementary outputs,

intended for driving a Loudspeaker: 80 mW on 50

Ω 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.

ST5088

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