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ST75C530

SUPER INTEGRATED DEVICES WITH DSP, AFE & MEMORIES FORTELEPHONY, MODEM, FAX OVERINTERNET & POTS LINES

STMicroelectronics 

ST75C530 - ST75C540

V - FUNCTIONAL DESCRIPTION (continued)

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-

Figure 3 : Handset/HandsfreeMode Operation

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

beenabledand disabledby software (see Figure 4).

2 TONE

GENERATOR

ATT_TX

DAC

MUTE

TxA1

15

14

HYBRID

Line

TxA2

ADC

11

RxA

CODER

DUAL

RAM

INTERFACE

AGC

AGC

2 TONE

DETECTORS

DG

Figure 4 : Handset Mode

HANDSFREE/

HANDSET

ALGORITHMS

DAC

ATT_MIC

ADC

MUTE

[0..-30]dB

Step 3dB

MUTE

MUTE

1

2

SPK1

76

SPK3

77

78

79

SPK2

9 MIC2

8

MIC1

10 MIC3

MIC2

_MIKGAIN

AGC = F(ILINE)

_TXGAIN

TxA1

TxA2

SPK2_1

SPK2_2

Softclipping

_SPKGAIN

AGC = F(ILINE)

DP_RING

RxA

15/84

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