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SA2532

sames

Receive

The receive input is the differential signal of RI and STB. The gain of the receive path is

2 dB (test circuit figure 5) with differential outputs, RO1/RO2 (0dB on SA2532C/U). When

mute is active during dialling the gain is reduced by > 60dB. During DTMF dialling a MF

comfort tone is applied to the receiver. The comfort tone is the DTMF signal with a level

that is -30dB relative to the line signal.

Side Tone

Side Tone is controlled along with Return Loss by a Double Balance Bridge as shown in

Fig. 1.

Figure 1

Double balance bridge (return loss and side tone) with one common ground

A good side tone cancellation is achieved by using the following equation:

ZBAL

=

R5

ZLINE

R1

The side tone cancellation signal is applied to the STB input.

Line Loss Compensation

When Line Loss Compensation is active the gain of the Transmit and Receive amplifiers

are changed by 6dB in accord with the DC conditions as measured at Pins LI and LS.

When the LLC Pin is Low this adjustment in gain occurs over the range I

When LLC is High the range is 45 to 75mA. Note that these figures apply for R1 = R30

Ω.

When the LLC Pin is open the amplifier gains remain fixed regardless of the Line Current.

ONE COMMON GROUND

DR-00708

RETURN LOSS

LINE

R2

R1

RI

SIDE TONE

R5

STB

SYN

LI