SSM2165-1P

Manufacturer Part NumberSSM2165-1P
Description10V; 700mW; microphone preamplifier with variable compression and noise gating. For microphone preamplifier/processor, computer sound cards, public address/paging systems
ManufacturerAnalog Devices
SSM2165-1P datasheet
 
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GENERAL DESCRIPTION
The SSM2165 is a complete and flexible solution for condition-
ing microphone inputs in computer audio systems. It is also
excellent for improving vocal clarity in communications and
public address systems. A low noise voltage controlled amplifier
(VCA) provides a gain that is dynamically adjusted by a control
loop to maintain a set compression characteristic. The compres-
sion ratio is set by a single resistor and can be varied from 1:1 to
over 15:1 relative to the fixed rotation point. Signals above the
rotation point are limited to prevent overload and to eliminate
“popping.” A downward expander (noise gate) prevents amplifi-
cation of noise or hum. This results in optimized signal levels
prior to digitization, thereby eliminating the need for additional
gain or attenuation in the digital domain that could add noise or
impair accuracy of speech recognition algorithms. The flexibility
of setting the compression ratio and the time constant of the
level detector, coupled with two values of rotation point, make
the SSM2165 easy to integrate in a wide variety of microphone
conditioning applications.
The SSM2165 is an ideal companion product for audio codecs
used in computer systems, such as the AD1845 and AD1847.
The device is available in 8-lead SOIC and P-DIP packages, and
guaranteed for operation over the extended industrial temperature
range of –40 C to +85 C. As shown in Figure 1a, the SSM2165-1
has a rotation point of –25.7 dBu (40 mV)
and gives –7.7 dBu (320 mV) before limiting. As shown in Figure
1b, the SSM2165-2 has a rotation point of –17.8 dBu (100 mV),
Patents pending.
1
All signals are in rms volts or dBu (0 dBu = 0.775 V rms).
Microphone Preamplifier with
Variable Compression and Noise Gating
AUDIO
IN+
a VCA gain of 8 dB and gives –9.8 dBu (250 mV) before limiting.
Both have a noise gate threshold of –64 dBu (500 V), below
which downward expansion reduces the gain with a ratio of
approximately 1:3. That is, a –3 dB reduction of output signal
occurs with a –1 dB reduction of input signal. For applications
requiring adjustable noise gate threshold, VCA gain up to 18 dB,
and adjustable rotation point, please refer to the SSM2166.
1
, a VCA gain of 18 dB,
SSM2165
FUNCTIONAL BLOCK DIAGRAM
C2
10 F
V+
+
BUF
VCA
OUT
IN
V+
C1
R
R
A
A
0.1 F
2
2
+1
VCA
BUFFER
LEVEL
CONTROL
DETECTOR
SSM2165
AVG CAP
+
R1
C3
25k
GND
22 F
0
–10
–20
–30
–40
–50
–60
–80
–70
–60
–50
–40
–30
–20
INPUT – dBu
0
–10
–20
–30
–40
–50
–60
–70
–80
–70
–60
–50
–40
–30
–20
INPUT – dBu
V
OUT
COMPRESSION
RATIO SET
–10
–10

SSM2165-1P Summary of contents