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| SA575 Datasheet, PDF (6/16 Pages) NXP Semiconductors – Low voltage compandor | |||
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SA575
Compressor
The typical compressor configuration is shown in
Figure 3. In this mode, the rectifier cell and variable gain
cell are in the feedback path. R6 and R7 provide the DC
feedback to the summing amplifier. The input is AC
coupled through C12 and output is AC coupled through C8.
In a system with inputs and outputs AC coupled, C8 and C12
could be eliminated and only R6, R7, C7, and C13 would be
required. If the external components R6, R7 and C7 are
eliminated, then the output of the summing amplifier will
motor-boat in absence of signals or at extremely low
signals. This is because there is no DC feedback path from
the output to input. In the presence of an AC signal this
phenomenon is not observed and the circuit will appear to
function properly.
The compressor gain expression and the attack and
release time constant is given by Equation 3 and
Equation 4, respectively.
Compressor gain = 3.8 kW x 100 mA 1/2
4VIN(avg)
(eq. 3)
where VIN(avg) = 0.95VIN(RMS)
tR = tA = 10 kW x CRECT = 10 kW x C4
(eq. 4)
VREF
8
R6
30kW
C7
R7
30kW
1mF
12
COMP IN
C12
10mF
13
10kW
S
14
C8
10mF
COMP OUT
DG
11
10kW
16
3.8kW
15
C9
2.2mF
C13
4.7mF
Figure 3. Typical Compressor Configuration
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