Low Voltage Microphone Preamplifier with
Variable Compression and Noise Gating
SSM2167
FEATURES
Complete microphone conditioner in a 10-lead package
Single 3 V operation
Low shutdown current < 2 μA
Adjustable noise gate threshold
Adjustable compression ratio
Automatic limiting feature prevents ADC overload
Low noise and distortion: 0.2% THD + N
20 kHz bandwidth
PIN CONFIGURATION
GND
1
VCA
IN 2
SHUTDOWN
3
BUF
OUT 4
INPUT
5
10
V
DD
OUTPUT
COMPRESSION RATIO
02628-001
SSM2167
TOP VIEW
(Not to Scale)
9
8
7
6
GATE THRS
AVG CAP
Figure 1. 10-Lead MSOP (RM Suffix)
APPLICATIONS
Desktop, portable, or palmtop computers
Telephone conferencing
Communication headsets
Two-way communications
Surveillance systems
Karaoke and DJ mixers
DOWNWARD
EXPANSION
THRESHOLD
(NOISE GATE)
LIMITING
THRESHOLD
(ROTATION POINT)
LIMITING
REGION
OUTPUT (dB)
COMPRESSION
REGION
1
r
VCA GAIN
GENERAL DESCRIPTION
The SSM2167 is a complete and flexible solution for conditioning
microphone inputs in personal electronics and computer audio
systems. It is also excellent for improving vocal clarity in com-
munications 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 charac-
teristic. The compression ratio is set by a single resistor and can
be varied from 1:1 to over 10:1 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 amplification of background 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. The flexibility of setting the compression ratio
and the time constant of the level detector, coupled with two
values of rotation point, make the SSM2167 easy to integrate in
a wide variety of microphone conditioning applications.
The device is available in a 10-lead MSOP package, and is
guaranteed for operation over the extended industrial
temperature range of −40°C to +85°C.
DOWNWARD
EXPANSION
REGION
1
1
V
DE
INPUT (dB)
V
RP
Figure 2. General Input/Output Characteristics
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2001–2007 Analog Devices, Inc. All rights reserved.
02628-002
SSM2167
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Pin Configuration ............................................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 4
Thermal Resistance ...................................................................... 4
ESD Caution .................................................................................. 4
Typical Performance Characteristics ............................................. 5
Applications Information ................................................................ 8
Theory of Operation .................................................................... 8
Signal Path ......................................................................................8
Level Detector ................................................................................9
Control Circuitry...........................................................................9
Setting the Compression Ratio ....................................................9
Setting the Noise Gate Threshold
(Downward Expansion) ............................................................ 10
Rotation Point (Limiting).......................................................... 10
Shutdown Feature....................................................................... 10
PCB Layout Considerations ...................................................... 10
Outline Dimensions ....................................................................... 11
Ordering Guide .......................................................................... 11
REVISION HISTORY
11/07—Rev. B to Rev. C
Updated Format .................................................................. Universal
Changes to PSRR .............................................................................. 3
Updated Outline Dimensions ....................................................... 11
Changes to Ordering Guide .......................................................... 11
9/03—Rev. A to Rev. B
Deleted SSM2167-2 Model ................................................ Universal
Changes to Ordering Guide ............................................................ 3
Edits to Figure 2 and Figure 3 ......................................................... 6
Updated Outline Dimensions ......................................................... 9
3/02—Rev. 0 to Rev. A
Edits to Specifications .......................................................................2
Edits to Figure 2 and Figure 3 ..........................................................6
7/01—Revision 0: Initial Version
Rev. C | Page 2 of 12
SSM2167
SPECIFICATIONS
V
S
= 3.0 V, f = 1 kHz, R
L
= 100 kΩ, R
COMP
= 0 Ω, T
A
= 25°C, V
IN
= 100 mV rms, R
GATE
= 2 kΩ, unless otherwise noted.
Table 1.
Parameter
AUDIO SIGNAL PATH
Voltage Noise Density
Noise
Total Harmonic Distortion + Noise
Input Impedance
Output Impedance
Load Drive
Input Voltage Range
Output Voltage Range
Gain Bandwidth Product
CONTROL SECTION
VCA Dynamic Gain Range
VCA Fixed Gain
Compression Ratio, Minimum
Compression Ratio, Maximum
Rotation Point
Noise Gate Range
POWER SUPPLY
Supply Voltage
Supply Current
DC Output Voltage
Power Supply Rejection Ratio
SHUTDOWN
Supply Current
Symbol
e
n
THD + N
Z
IN
Z
OUT
Conditions
10:1 compression
20 kHz bandwidth, V
IN
= GND
V
IN
= 100 mV rms
Min
Typ
20
−70
0.2
100
145
5
2
600
700
1
40
18
1:1
10:1
63
−40
2.5
2.3
1.4
45
2
5.5
5
Max
Unit
nV/√Hz
dBV
%
kΩ
Ω
kΩ
nF
mV rms
mV rms
MHz
dB
dB
Minimum resistive load
Maximum capacitive load
0.4% THD + N
0.4% THD + N
1:1 compression, VCA G = 18 dB
See Table 4 for R
COMP
Maximum threshold
V
SY
I
SY
PSRR
I
SY
V
SY
= 2.5 V to 6 V
Pin 3 = GND
mV rms
dBV
V
mA
V
dB
μA
8
Rev. C | Page 3 of 12
SSM2167
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter
Supply Voltage
Input Voltage
Operating Temperature Range
Junction Temperature
Lead Temperature (Soldering, 10 sec)
883 (Human Body) Model
Rating
6V
6V
−40°C to +85°C
150°C
300°C
500 V
THERMAL RESISTANCE
θ
JA
is specified for worst-case conditions, that is, θ
JA
is specified
for device soldered in 4-layer circuit board for surface-mount
packages.
Table 3.
Package Type
10-Lead MSOP (RM)
θ
JA
180
θ
JC
35
Unit
°C/W
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. C | Page 4 of 12
SSM2167
TYPICAL PERFORMANCE CHARACTERISTICS
100
T
A
= 25°C
V+ = 3V
R
LOAD
= 100kΩ
COMPRESSION RATIO 2:1
ROTATION POINT = 63mV rms
1
NOISE GATE (mV rms)
THD + N (%)
10
0.1
0
500
1000
1500
2000
2500
3000
3500
02628-003
0.1
INPUT VOLTAGE (V rms)
1
R
GATE
(Ω)
Figure 3. Noise Gate vs. R
GATE
Figure 6. THD + N vs. Input
1
T
A
= 25°C
V+ = 3V
V
IN
= 24.5mV rms
COMPRESSION RATIO 1:1
ROTATION POINT = 63mV rms
NOISE GATE SETTING = 1.4V rms
OUTPUT (dBV)
0
COMPRESSION RATIO 10:1
–10
–20
COMPRESSION RATIO 5:1
–30
COMPRESSION RATIO 2:1
–40
COMPRESSION RATIO 1:1
–50
–60
–70
T
A
= 25°C
V+ = 3V
R
LOAD
= 100kΩ
ROTATION POINT = 63mV rms
NOISE GATE SETTING = 1.4V rms
–70
–60
–50
–40
–30
–20
–10
02628-007
02628-008
THD + N (%)
0.1
100
1k
FREQUENCY (Hz)
10k
30k
02628-004
0.01
20
–80
–80
INPUT (dBV)
Figure 4. THD + N vs. Frequency
Figure 7. Output vs. Input Characteristics
35
30
25
20
PSRR (dB)
GAIN (dB)
–10
–20
–30
–40
–50
–60
V
IN
= 2mV rms
R
COMP
= 175kΩ
ROTATION POINT = 63mV rms
NOISE GATE SETTING = 1.4V rms
02628-005
V+ = 3V + 0.1
R
GATE
= 5kΩ
R
COMP
= 0V
15
10
5
0
–5
–10
–15
1k
–70
–80
10
10k
100k
FREQUENCY (Hz)
1M
10M
100
1k
FREQUENCY (Hz)
10k
100k
Figure 5. GBW Curves vs. VCA Gain
Figure 8. PSRR vs. Frequency
Rev. C | Page 5 of 12
02628-006
1
0.01
0.01
T
A
= 25°C
V+ = 3V
V
IN
FREQUENCY = 1kHz
R
LOAD
= 100kΩ
COMPRESSION RATIO 1:1
ROTATION POINT = 63mV rms
NOISE GATE SETTING = 1.4V rms
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