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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.3.12.2 - Handsfree Mode

The ha ndsfree uses a MIC1 and a SPK1 as microphone and loudspeaker interface (see Figure 6).

Figure 6 : Handsfree Mode : Full Duplex

MIC1

_MIKGAIN

+

-

ACOUSTIC

FILTER

ADAPTIVE

ATTENUATOR

AGC = F(IL)

_TXGAIN

TxA1

TxA2

ADAPTIVE

FIR

FILTER

NLMS

CONTROL

NLMS

ADAPTIVE

FIR

FILTER

SPK1P

SPK1N

_SPKGAIN

AGC = F(IL)

Softclipping

ADAPTIVE

ATTENUATOR

-

RxA

+

Tx Characteristics

Symbol

Parameter

Gtx Transmit Gain

Ntx

Mmic

Dtx

Transmit noise

Microphone mute

Transmit distortion

Test Conditions

Min.

_MIKGAIN=7FFF,_TXGAIN=7FFF ,AGC disabled,

VMIC1 = -21dBV

2kΩ between MIC1 and GND

VMIC1 = - dBV

_MIKGAIN=7FFF,_TXGAIN=7FFF ,AGC disabled,

VMIC1 = -9dBV

Typ.

24

-70

60

Max. Unit

dB

dBmp

dB

2%

Rx Characteristics

Symbol

Grx

Mrx

Dtx

Parameter

Receive Gain

Mute

Receive distortion

(SPK1 output)

Test Conditions

_SPKGAIN=7FFF, AGC disabled, VRXA = -33dBV

_SPKGAIN=7FFF, AGC disabled, VRXA = -33dBV

Min.

Typ.

24

60

Max.

2

Unit

dB

dB

%

AGC

The AGC has the same behavior as in Handset mode. Furthermore, the maximum gain added by AGC can

be fixed by using the RX_GAINMAX and TX_GAINMAX registers.

Softclipping

See Figure 7.

System Stability

Parameter

Test Conditions

Min.

Loop attenuation in Rx RxA to TxA1-TxA2

Speaker gain is 12dB, Mike gain is 14dB 20

Loop attenuation in Tx MICx to SPK1P-SPK1N Analogique sidetone not used

20

(see DAA schematics)

Typ.

Max.

Unit

dB

dB

It is possible to add some gain switching in the Tx and Rx path (to reduce the gain of the loop) by using

the GAIN_RCV and GAIN_XMT registers.

17/84

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