¡ Semiconductor

MSM7524

7/21

Special tone input and gain adjustment.

FXI- and GS3 are connected to the inverting input and the output of

the on-chip operational amplifiers (IV). The inverting input of the

amplifier (IV) is internally connected to SG.

When not using the special tone detect function, FXI- and GS3

should be wired to each other.

Regarding the gain adjustment, refer to Fig. 3.

Pin No.

Name

I/O

28

FXI–

I

Description

Two input and output pins of the on-chip operational amplifier (V).

These pins are useful to implement the pre-amplifier for Call

Progress Tone receiving.

Refer to Fig. 1.

Voltage gain should be less than 10 (20 dB).

Detect and non-detect amplitude are specified as the receive signal

level at GS2.

30

CPI+

I

R2

R3

SG

IN

C1

FXI-

GS3

–

+

• R2, R3,

≥ 50 kW, C1 = 2.2 µF

• Voltage Gain; R3/R2

£ 10 (20 dB)

Figure 3 Receive Gain Adjustment for FX

31

CPI–

I

32

GS2

O

29

GS3

O