Analog Devices SSM2165 Datasheet

VCA

+1

VCA

IN

BUF

OUT

V+

V+

+

C2

10mF

BUFFER

LEVEL
DETECTOR

CONTROL

SSM2165

C1

0.1mF

AUDIO

IN+

V

OUT

R1

25kV

C3

22mF

AVG CAP

COMPRESSION
RATIO SET

GND

R

A

2

R

A

2

+

Microphone Preamplifier with

a

Variable Compression and Noise Gating

FEATURES
Complete Microphone Conditioner in an 8-Lead Package
Single +5 V Operation
Preset Noise Gate Threshold
Compression Ratio Set by External Resistor
Automatic Limiting Feature Prevents ADC Overload
Adjustable Release Time
Low Noise and Distortion
20 kHz Bandwidth (ⴞ1 dB)
Low Cost

APPLICATIONS
Microphone Preamplifier/Processor
Computer Sound Cards
Public Address/Paging Systems
Communication Headsets
Telephone Conferencing
Guitar Sustain Effects Generator
Computerized Voice Recognition
Surveillance Systems
Karaoke and DJ Mixers

GENERAL DESCRIPTION

The SSM2165 is 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 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 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),

*

Patents pending.

1

All signals are in rms volts or dBu (0 dBu = 0.775 V rms).

REV. A

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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

1

, a VCA gain of 18 dB,

SSM2165*

FUNCTIONAL BLOCK DIAGRAM

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 µV), 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.

0

–10

–20

–30

–40

OUTPUT – dBu

–50

–60

INPUT – dBu

Figure 1a. SSM2165-1 Compression and Gating Characteristics

0

–10

–20

–30

–40

OUTPUT – dBu

–50

–60

–70

INPUT – dBu

Figure 1b. SSM2165-2 Compression and Gating Characteristics

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1999

–10–80 –70 –60 –50 –40 –30 –20

–10–80 –70 –60 –50 –40 –30 –20

SSM2165–SPECIFICATIONS

(V+ = +5 V, f = 1 kHz, RL = 100 k⍀, R

= 0 ⍀, TA = +25ⴗC, unless otherwise noted)

COMP

Parameter Symbol Conditions Min Typ Max Units

AUDIO SIGNAL PATH

Voltage Noise Density

e

n

15:1 Compression, V

= GND 17 nV/√Hz

IN

Noise 20 kHz Bandwidth, VIN = GND –109 dBu

2

1

Total Harmonic Distortion THD+N

SSM2165-1 2nd and 3rd Harmonics, V
SSM2165-2 2nd and 3rd Harmonics, V

= –30 dBu 0.2 0.5 %

IN

= –20 dBu 0.2 0.5 %

IN

22 kHz Low-Pass Filter
Input Impedance Z
Output Impedance Z

IN

OUT

180 kΩ
75 Ω

Load Drive Resistive 5 kΩ

Capacitive 2 nF
Input Voltage Range 1% THD 1 V rms
Output Voltage Range 1% THD 1.4 V rms
Gain Bandwidth Product 1:1 Compression

SSM2165-1 VCA G = 18 dB 300 kHz
SSM2165-2 VCA G = 8 dB 100 kHz

CONTROL SECTION

VCA Dynamic Gain Range 40 dB
VCA Fixed Gain

SSM2165-1 18 dB
SSM2165-2 8dB

Rotation Point

SSM2165-1 40 mV rms

SSM2165-2 100 mV rms
Compression Ratio, Min 1:1
Compression Ratio, Max 15:1

Control Feedthrough 15:1 Compression ±5mV

POWER SUPPLY

Supply Voltage Range V
Supply Current I

S

SY

4.5 5.5 V

7.5 10 mA
Quiescent Output Voltage Level 2.2 V
Power Supply Rejection Ratio2PSRR 50 dB

NOTES

1

0 dBu = 0.775 V rms.

2

Referred to input.

Specifications subject to change without notice.

–2–

REV. A

SSM2165

ABSOLUTE MAXIMUM RATINGS

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +10 V

Audio Input Voltage . . . . . . . . . . . . . . . . . . . . . Supply Voltage

Operating Temperature Range . . . . . . . . . . . . –40°C to +85°C

Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C

Junction Temperature (T

) . . . . . . . . . . . . . . . . . . . . . .+150°C

J

Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . .+300°C

ESD RATINGS

883 (Human Body) Model . . . . . . . . . . . . . . . . . . . . . . . 2.0 kV

THERMAL CHARACTERISTICS

Thermal Resistance

8-Lead Plastic DIP

θ

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103°C/W

JA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43°C/W

θ

JC

8-Lead SOIC

θ

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158°C/W

JA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43°C/W

θ

JC

ORDERING GUIDE

Temperature Package Package

Model Range Description Options

SSM2165-1P –40°C to +85°C Plastic DIP N-8
SSM2165-2P –40°C to +85°C Plastic DIP N-8
SSM2165-1S –40°C to +85°C Narrow SOIC SO-8
SSM2165-2S –40°C to +85°C Narrow SOIC SO-8

PIN CONFIGURATION

GND

VCA

BUF

OUT

AUDIO +IN

1
2

IN

3
4

SSM2165

TOP VIEW

(Not to Scale)

8

V+

7

OUTPUT

6

COMP RATIO SET

5

AVG CAP

PIN FUNCTION DESCRIPTIONS

Pin # Mnemonic Function

1 GND Ground
2 VCA

IN

VCA Input Pin. A typical

connection is a 1 µF–10 µF

capacitor from the buffer output
pin (Pin 3) to this pin.

3 BUF

OUT

Input Buffer Amplifier Output
Pin. Must not be loaded by
capacitance to ground.

4 AUDIO +IN Input Audio Signal. The input

signal should be ac-coupled

(0.1 µF typical) into this pin.

5 AVG CAP Detector Averaging Capacitor.

A capacitor, 2.2 µF–22 µF, to

ground from this pin is the
averaging capacitor for the
detector circuit.

6 COMP RATIO SET Compression Ratio Set Pin. A

resistor to ground from this pin
sets the compression ratio as

shown in Figure 1.
7 OUTPUT Output Signal.
8 V+ Positive Supply, +5 V Nominal.

CAUTION

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.

REV. A

–3–

WARNING!

ESD SENSITIVE DEVICE