SA2532
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
RETURN LOSS
SIDE TONE
LINE
RI
R1
LI
SYN
R2
R5
STB
L
V
S S
ONE COMMON GROUND
DR-00708
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
ZLINE
=
R5
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
LINE
= 20 to 50 mA.
When LLC is High the range is 45 to 75mA. Note that these figures apply for R1 = R30Ω.
When the LLC Pin is open the amplifier gains remain fixed regardless of the Line Current.
4/22
sames
Z
B
Z
R
E
F
A
SAMES [ SAMES ]
