SSM-2120 Analog, SSM-2120 Datasheet - Page 7

• Manufacturer Part Number: SSM-2120
• Description: (SSM-2122) Dynamic Range Processors/Dual VCA
• Manufacturer: Analog

Input Signal
Increase (dB)
20
20
20
20
20
20
20
20
*AGC for Compression Only.
REV. C
signal will be dependent on the noise of the current-to-voltage
converter amplifier if the expansion ratio is high enough.
As discussed in the Threshold Control section, the use of the
control circuit of Figure 6, including the R
diodes, yields positive unipolar control outputs.
COMPANDING NOISE REDUCTION SYSTEM
A complete companding noise reduction system is shown in
Figure 10. Normally, to obtain an overall gain of unity, the
value of R
compression/expansion ratio.
Table II shows compression/expansion ratios ranging from 1.5:1
to full limiting with the corresponding values of R
An example of a 2:1 compression/expansion ratio is plotted in
Figure 11. Note that signal compression increases gain for low
level signals and reduces gain for high levels while expansion
does the reverse. The net result for the system is the same as the
original input signal except that it has been compressed before
being sent to a given medium and expanded after recovery. The
compression/expansion ratio needed depends on the medium
SIGNAL
C
INPUT
is equal to R
Gain
(Reduction
or Increase)
(dB)
6.67
10.00
13.33
15.00
16.00
17.33
18.00
20.00
10k
1µF
36k
47
REC
E
. The values of R
IN
2200pF
200
200
|I
1µF
I N
|
+V
–V
V+
V–
C
C
Compressor
Only
Output Signal
Increase (dB)
13.33
10.00
6.67
5.00
4.00
2.67
2.00
0
LOG AV
4.7M
Figure 10. Companding Noise Rejection System
PV
C/E
1k
to V+ and two
will determine the
R
C
C/E
10pF
36
39k
.
V–
V+
Expander
Only
Output Signal
Increase (dB)
22.67
30.00
33.33
35.00
36.00
37.33
38.00
40.00
TRANSMISSION
10k
STORAGE
Table II.
MEDIUM
OR
–7–
being used. As an extreme example, a household tape player
would require a higher compression/expansion ratio than a
professional stereo system.
Figure 11. Companding Noise Reduction with 2:1
Compression/Expansion Ratio
10k
1µF
36k
–20
–40
–60
–80
47
20
0
REC
–80
Compression/
Expansion Ratio
1.5:1
2:1
3:1
4:1
5:1
7.5:1
10:1
AGC*/Limiter
IN
2200pF
I
R
REF
200
200
REF
|I
1µF
I N
|
= 4.7M
–60
3µA
–V
+V
V+
V–
INPUT SIGNAL LEVEL – dB
C
C
LOG AV
4.7M
–40
EXPANSION
SSM2120/SSM2122
1k
RESPONSE
OVERALL
R
E
2:1
–20
10pF
36k
R
5,800
5,133
4,800
4,244
11,800
7,800
4,415
3,800
39k
C/E
2:1
COMPRESSION
V–
V+
0
10k
SIGNAL
OUTPUT
(mV/dB)
2.0
3.0
4.0
4.5
4.8
5.2
5.4
6.0
V
CONTROL
20
25dB
–