SSM2165 Analog Devices, SSM2165 Datasheet

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SSM2165

Manufacturer Part Number
SSM2165
Description
Microphone Preamplifier with Variable Compression & Noise Gating
Manufacturer
Analog Devices
Datasheet

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a
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),
1
All signals are in rms volts or dBu (0 dBu = 0.775 V rms).
Patents pending.
1
, a VCA gain of 18 dB,
Variable Compression and Noise Gating
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.
AUDIO
Microphone Preamplifier with
IN+
0.1 F
C1
–10
–20
–30
–40
–50
–60
–70
–10
–20
–30
–40
–50
–60
FUNCTIONAL BLOCK DIAGRAM
0
0
–80
–80
SSM2165
–70
–70
GND
V+
V+
+1
BUFFER
BUF
–60
–60
LEVEL
DETECTOR
OUT
INPUT – dBu
INPUT – dBu
AVG CAP
–50
–50
R
10 F
2
22 F
A
C2
C3
+
–40
–40
R
VCA
2
SSM2165
+
A
25k
–30
–30
IN
CONTROL
R1
VCA
–20
–20
COMPRESSION
RATIO SET
–10
–10
V
OUT

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SSM2165 Summary of contents

Page 1

... 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 – + 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 – ...

Page 2

... Input Voltage Range Output Voltage Range Gain Bandwidth Product SSM2165-1 SSM2165-2 CONTROL SECTION VCA Dynamic Gain Range VCA Fixed Gain SSM2165-1 SSM2165-2 Rotation Point SSM2165-1 SSM2165-2 Compression Ratio, Min Compression Ratio, Max Control Feedthrough POWER SUPPLY Supply Voltage Range Supply Current ...

Page 3

... ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the SSM2165 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality ...

Page 4

... –30dBu (– 100k L 1 SSM2165–1 0.1 SSM2165–2 0.050 20 100 1k FREQUENCY – Hz SSM2165–2 10:1 15 SSM2165– SSM2165–2 –10 – –30 –40 –50 –60 –70 10k 30k 100 COMPRESSION RATIO ...

Page 5

... A downward expansion (noise gating) feature reduces background and circuit noise below 500 V. The rotation point determines the output signal levels before limiting (referred to the input), and for the SSM2165-1 and 100 mV for the SSM2165-2. LIMITING THRESHOLD ...

Page 6

... C3 GND 22 F The bandwidth of the SSM2165 is quite wide at all gain set- tings. The upper –3 dB point is approximately 300 kHz. The GBW plots are shown in TPC 5. While the noise of the input buffer is fixed, the input referred noise of the VCA is a function of gain ...

Page 7

... That is, in the limiting region change of input results change of output. The rotation point is set (–26 dBu) for the SSM2165-1 and 100 mV (–18 dBu) for the SSM2165-2. In the SSM2165, limiting is compression at a fixed compression ratio of approxi- mately 15:1 ...

Page 8

... Reduce the input gradually until the output falls off more rapidly. This point is the noise gate threshold, and should be approximately 500 V (–64 dBu). The noise gate threshold on the SSM2165 is fixed at 500 V, a practical value for many microphones. Should a different noise gate threshold be required, consider using the SSM2166. ...

Page 9

... Power-down and mute functions are also built in. Custom- ized versions of the SSM2165 are available for large volume LIMITING REGION users. The wide dynamic range of the SSM2165 makes it useful in many applications other than microphone signal conditioning such as a sustain generator for guitars. For further information, contact your Analog Devices representative ...

Page 10

... SSM2165 Revision History Location Data Sheet changed from REV REV. B. Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Page ...

Page 11

... SEATING 0.070 (1.77) PLANE 0.014 (0.356) 0.045 (1.15) 8-Lead Narrow-Body SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80 0.2440 (6.20) 0.1574 (4.00) 0.2284 (5.80) 0.1497 (3.80 PIN 1 0.0500 (1.27) BSC 0.0688 (1.75) 0.0098 (0.25) 0.0532 (1.35) 0.0040 (0.10) 0.0192 (0.49) 0.0098 (0.25) SEATING 0.0138 (0.35) PLANE 0.0075 (0.19) SSM2165 0.195 (4.95) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) 0.0196 (0.50) 45 0.0099 (0.25) 8 0.0500 (1.27) 0 0.0160 (0.41) ...

Page 12

... SSM2165 ...

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