SSM2166_15 Datasheet, PDF (1/20 Pages) Analog Devices – Microphone Preamplifier with Variable Compression and Noise Gating

Data Sheet
Microphone Preamplifier with
Variable Compression and Noise Gating
SSM2166
FEATURES
Complete microphone conditioner in a 14-lead SOIC package
Single 5 V operation
Adjustable noise gate threshold
Compression ratio set by external resistor
Automatic limiting feature—prevents ADC overload
Adjustable release time
Low noise and distortion
Power-down feature
20 kHz bandwidth (±1 dB)
APPLICATIONS
Microphone preamplifiers/processors
Computer sound cards
Public address/paging systems
Communication headsets
Telephone conferencing
Guitar sustain effects generators
Computerized voice recognition
Surveillance systems
Karaoke and DJ mixers
GENERAL DESCRIPTION
The SSM2166 integrates a complete and flexible solution for
conditioning 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
compression ratio is set by a single resistor and can be varied
from 1:1 to over 15:1 relative to a user-defined rotation point;
signals above the rotation point are limited to prevent overload
and to eliminate popping. In the 1:1 compression setting, the
SSM2166 can be programmed with a fixed gain of up to 20 dB;
this gain is in addition to the variable gain in other compression
settings. The input buffer can also be configured for front-end
gains of 0 dB to 20 dB. A downward expander (noise gate) prevents
amplification 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 may
add noise or impair accuracy of speech recognition algorithms.
The compression ratio and time constants are set externally. A
high degree of flexibility is provided by the VCA gain, rotation
point, and noise gate adjustment pins.
The SSM2166 is an ideal companion product for audio codecs
used in computer systems. The SSM2166 is available in a 14-
lead SOIC package and is guaranteed for operation over the
extended industrial temperature range of −40°C to +85°C.
10
0
COMP RATIO = 10:1
–10
COMP RATIO = 2:1
–20
COMP RATIO = 1:1
–30
–40
–50
–60
–70
–60
–50
–40
–30
–20
–10
0
INPUT (dBu)
Figure 1. Compression and Gating Characteristics with 10 dB of Fixed Gain (The
Gain Adjust Pin Can Be Used to Vary This Fixed Gain Amount)
FUNCTIONAL BLOCK DIAGRAM AND TYPICAL SPEECH APPLICATION
R1
10kΩ
10µF
+
10µF (OPTIONAL)
+
V+
BUF OUT VCAIN VCAR
5
3
4
V+
14
GAIN
ADJUST
AUDIO
+IN
–IN
6
0.1µF
7
BUFFER
1kΩ
1kΩ
VCA
2
2.3kΩ
OUTPUT
13 _{NOISE GATE}
SET
9
R2
10kΩ
+
1µF
LEVEL
DETECTOR
SSM2166
CONTROL
500kΩ
17kΩ
11
ROTATION
12
1
8
10
SET
POWER DOWN
GND
AVG CAP ₊
COMP RATIO SET
22µF 25kΩ
Figure 2.
Rev. E
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