Datasheet SSM2166 (Analog Devices)

Microphone Preamplifier with Variable Compression and Noise Gating Data Sheet SSM2166 FEATURES
and to eliminate popping. In the 1:1 compression setting, the SSM2166 can be programmed with a fixed gain of up to 20 dB;
Complete microphone conditioner in a 14-lead SOIC package
this gain is in addition to the variable gain in other compression
Single 5 V operation Adjustable noise gate threshold
settings. The input buffer can also be configured for front-end
Compression ratio set by external resistor
gains of 0 dB to 20 dB. A downward expander (noise gate) prevents
Automatic limiting feature—prevents ADC overload
amplification of noise or hum. This results in optimized signal
Adjustable release time
levels prior to digitization, thereby eliminating the need for
Low noise and distortion
additional gain or attenuation in the digital domain that may
Power-down feature
add noise or impair accuracy of speech recognition algorithms.
20 kHz bandwidth (±1 dB)
The compression ratio and time constants are set externally. A high degree of flexibility is provided by the VCA gain, rotation
APPLICATIONS
point, and noise gate adjustment pins.
Microphone preamplifiers/processors
The SSM2166 is an ideal companion product for audio codecs
Computer sound cards
used in computer systems. The SSM2166 is available in a 14-lead
Public address/paging systems
SOIC package and is guaranteed for operation over the
Communication headsets
extended industrial temperature range of −40°C to +85°C.
Telephone conferencing 10 Guitar sustain effects generators Computerized voice recognition 0 COMP RATIO = 10:1 Surveillance systems –10 Karaoke and DJ mixers COMP RATIO = 2:1 ) GENERAL DESCRIPTION Bu –20 d ( UT COMP RATIO = 1:1
The SSM2166 integrates a complete and flexible solution for
P –30 UT
conditioning microphone inputs in computer audio systems. It
O
is also excellent for improving vocal clarity in communications
–40
and public address systems. A low noise, voltage-controlled
–50
amplifier (VCA) provides a gain that is dynamically adjusted by a control loop to maintain a set compression characteristic. The
–60
2
–70 –60 –50 –40 –30 –20 –10 0
-00 compression ratio is set by a single resistor and can be varied 57
INPUT (dBu)
003 from 1:1 to over 15:1 relative to a user-defined rotation point; Figure 1. Compression and Gating Characteristics with 10 dB of Fixed Gain (The signals above the rotation point are limited to prevent overload Gain Adjust Pin Can Be Used to Vary This Fixed Gain Amount)
FUNCTIONAL BLOCK DIAGRAM AND TYPICAL SPEECH APPLICATION R1 V+ 10µF 10µF (OPTIONAL) 10kΩ + + BUF OUT VCA V+ IN VCAR GAIN 5 3 4 14 ADJUST 2 BUFFER 1kΩ 2.3kΩ –IN 6 OUTPUT 0.1µF 1kΩ VCA 13 AUDIO NOISE GATE 7 +IN SET 9 R2 LEVEL 500kΩ CONTROL 10kΩ DETECTOR 17kΩ 11 +1µF SSM2166 ROTATION SET 12 1 8 10 POWER DOWN GND AVG CAP COMP RATIO SET +22µF 25kΩ
01 0 7- 035 0 Figure 2.
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Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM AND TYPICAL SPEECH APPLICATION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLICATIONS INFORMATION SIGNAL PATH LEVEL DETECTOR CONTROL CIRCUITRY Compression Ratio Rotation Point VCA Gain Setting and Muting Downward Expansion Threshold POWER-DOWN FEATURE PCB LAYOUT CONSIDERATIONS OUTLINE DIMENSIONS ORDERING GUIDE