SSM2166_03 Datasheet, PDF (1/16 Pages) Analog Devices – Microphone Preamplifier with Variable Compression and Noise Gating

Microphone Preamplifier with
Variable Compression and Noise Gating
SSM2166^*
FEATURES
Complete Microphone Conditioner in a 14-Lead 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)
Low Cost
APPLICATIONS
Microphone Preamplifier/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 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 opti-
mized 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 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, such as the AD1845 and AD1847.
The device is available in a 14-lead SOIC package, and is guar-
anteed for operation over the extended industrial temperature
range of –40°C to +85°C. For similar features and performance
in an 8-lead package, please refer to the SSM2165.
10
RATIO = 10:1
0
–10
RATIO = 2:1
–20
–30
RATIO = 1:1
–40
–50
–60
–70
–60
–50
–40
–30
–20
–10
0
INPUT – dBu
Figure 1. SSM2166 Compression and Gating Char-
acteristics with 10 dB of Fixed Gain (The Gain Adjust
Pin Can Be Used to Vary This Fixed Gain Amount)
*Patents pending.
REV. B
R1 = 10k⍀
10␮F
+
10␮F*
+
V+
5
34
14
–IN ⁶
AUDIO
7
+IN
0.1␮F
BUFOUT VCA_IN
VCA_R
V+
1k⍀
BUFFER
1k⍀ VCA
2 ^2.3k⍀
VCA GAIN
13 ADJ
OUTPUT
9 500k⍀
R2 = 10k⍀
SSM2166
LEVEL
DETECTOR
CONTROL
NOISE GATE
SET
11 ^17k⍀
+
1␮F
12
POWER
DOWN
1
GND
AVG
8 + ¹⁰
CAP ^22␮F
25k⍀
ROTATION
COMPRESSION ^{POINT SET}
RATIO
SET
*OPTIONAL
Figure 2. Functional Block Diagram and Typical Speech Application
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