SA575DTBG Datasheet, PDF (7/16 Pages) ON Semiconductor – Low Voltage Compandor

SA575
Automatic Level Control
The typical Automatic Level Control circuit
configuration is shown in Figure 4. It can be seen that it is
quite similar to the compressor schematic except that the
input to the rectifier cell is from the input path and not from
the feedback path. The input is AC coupled through C₁₂
and C₁₃ and the output is AC coupled through C₈. Once
again, as in the previous cases, if the system input and
output signals are already AC coupled, then C₁₂, C₁₃ and
C₈ could be eliminated. Concerning the compressor,
removing R₆, R₇ and C₇ will cause motor-boating in
absence of signals. C_COMP is necessary to stabilize the
summing amplifier at higher input levels. This circuit
provides an input dynamic range greater than 60 dB with
the output within "0.5 dB typical. The necessary design
expressions are given by Equation 5 and Equation 6,
respectively.
3.8 kW x 100 mA
ALC gain =
4V_IN(avg)
(eq. 5)
t_R = t_A = 10 kW x C_RECT = 10 kW x C₉
(eq. 6)
V_REF
8
R₆
30kW
C7
R₇
30kW
1mF
C COMP
22pF
12
ALC IN
C₁₂
13
10mF
10kW
DG
S
14
11
10kW
C₁₃
16
4.7mF
3.8kW
15
C₉
2.2mF
C₈
10mF
ALC OUT
Figure 4. Typical ALC Configuration
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