ST75C540 datasheet(15/84 Pages) STMICROELECTRONICS

15 / 84 page

V.3.12 - Telephony Functions

ST75C530/540 telephony software provides both

handset and handsfree modes. ST75C530/540 is

connected to the phone line through a D.A.A.,

handset and loudspeaker are connected to

ST75C530/540 through amplifiers.

Though the D.A.A. has to comply with modem/fax

regulations in most of the applications, the micro-

phone and the earphone amplifier gains will be

adjusted in compliance with the telephony regula-

tions. The software implementedin ST75C530/540

allows functions such as softclipping, AGC in both

modes, and full duplex mode in handsfree(see Fig-

ure 3).

V.3.12.1 - Handset Mode

In handset mode, all the attenuations (_SPKGAIN,

_TXGAIN, _MIKGAIN) are from 0dB to -inf

(32768 steps). AGC and softclipping functions can

be enabledand disabled by software (see Figure 4).

DUAL

RAM

INTERFACE

ADC

MUTE

DAC

Line

HYBRID

TxA1

TxA2

RxA

ADC

10 MIC3

MIC1

MIC2

SPK2

MUTE

SPK3

MUTE

SPK1

MUTE

[0..-30]dB

Step 3dB

DAC

ATT_TX

CODER

HANDSFREE/

HANDSET

ALGORITHMS

ATT_MIC

2 TONE

GENERATOR

AGC

2 TONE

DETECTORS

AGC

Figure 3 : Handset/HandsfreeMode Operation

V - FUNCTIONAL DESCRIPTION (continued)

MIC2

SPK2_1

SPK2_2

_MIKGAIN

_SPKGAIN

Softclipping

AGC = F(I

LINE)

RxA

DP_RING

TxA1

TxA2

_TXGAIN

AGC = F(I

LINE)

Figure 4 : Handset Mode

ST75C530 - ST75C540

15/84

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