Analog Devices SSM2166 b Datasheet

Microphone Preamplifier with

Variable Compression and Noise Gating

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 (ⴞ1 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;

SSM2166

*

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 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 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 guar­anteed 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

–20

–30

OUTPUT – dBu

–40

–50

–60

–70 0–60 –50 –40 –30 –20 –10

RATIO = 2:1

RATIO = 1:1

INPUT – dBu

Figure 1. SSM2166 Compression and Gating Char­acteristics with 10 dB of Fixed Gain (The Gain Adjust
Pin Can Be Used to Vary This Fixed Gain Amount)

R1 = 10k⍀

BUFOUT

6

–IN

0.1␮F

7

POWER

DOWN

AUDIO

+IN

R2 = 10k⍀

+

1␮F

*Patents pending.

REV. B

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. 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 companies.

Figure 2. Functional Block Diagram and Typical Speech Application

SSM2166

12

BUFFER

1

GND

10␮F

53

VCA

LEVEL

DETECTOR

AVG
CAP

10␮F

++

IN

22␮F

*

4

VCA

R

1k⍀

VCA1k⍀

CONTROL

10

8

+

25k⍀

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] © 2003 Analog Devices, Inc. All rights reserved.

14

V+

COMPRESSION
RATIO
SET

*

2.3k⍀

2

VCA GAIN

ADJ

13

OUTPUT

500k⍀

9

NOISE GATE

11

ROTATION
POINT SET

OPTIONAL

SET

17k⍀

V+

SSM2166–SPECIFICATIONS

(V+ = 5 V, f = 1 kHz, RL = 100 k⍀, R
R1 = 0 ⍀, R2 = ⴥ⍀, TA = 25ⴗC, unless otherwise noted, VIN = 300 mV rms.)

= 600 k⍀, R

GATE

ROTATION

= 3 k⍀, R

COMP

= 0 ⍀,

Parameter Symbol Conditions Min Typ Max Unit

AUDIO SIGNAL PATH

Voltage Noise Density

e

n

Noise 20 kHz Bandwidth, VIN = GND –109 dBu

15:1 Compression 17 nV/√Hz

1

Total Harmonic Distortion THD+N 2nd and 3rd Harmonics, VIN = –20 dBu 0.25 0.5 %

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
Buffer

Input Voltage Range 1% THD 1 V rms
Output Voltage Range 1% THD 1 V rms

VCA

Input Voltage Range 1% THD 1 V rms
Output Voltage Range 1% THD 1.4 V rms

Gain Bandwidth Product 1:1 Compression, VCA G = 60 dB 30 MHz

CONTROL SECTION

VCA Dynamic Gain Range 60 dB
VCA Fixed Gain Range –60 to +19 dB
Compression Ratio, Min 1:1
Compression Ratio, Max See TPC 3 for R

COMP/RROT

15:1

Control Feedthrough 15:1 Compression, Rotation Point = –10 dBu ±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 Ratio PSRR 50 dB

POWER DOWN

Supply Current Pin 12 = V+

NOTES

1

0 dBu = 0.775 V rms.

2

Normal operation: Pin 12 = 0 V.

Specifications subject to change without notice.

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

2

10 100 µA

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

SSM2166S –40°C to +85°CNarrow SOIC R-14

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

ESD RATINGS

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

THERMAL CHARACTERISTICS

Thermal Resistance

14-Lead SOIC

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120°C/W

θ

JA

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36°C/W

θ

JC

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
SSM2166 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. B–2–

SSM2166

PIN FUNCTION DESCRIPTIONS

Pin No. Mnemonic Function

1GND Ground
2 GAIN ADJUST VCA Gain Adjust Pin. A resistor from this pin to ground sets the fixed gain of the VCA.

To check the setting of this pin, make sure the compression pin (Pin 10) is grounded for
no compression. The gain can be varied from 0 dB to 20 dB. For 20 dB, leave the pin
open. For 0 dB of fixed gain, a typical resistor value is approximately 1 kΩ. For 10 dB
of fixed gain, the resistor value is approximately 2 kΩ to 3 kΩ. For resistor values <1 kΩ,
the VCA can attenuate or mute. Refer to TPC 4.

3 VCA

4 VCA

IN

R

5 BUF OUT Input Buffer Amplifier Output Pin. Must not be loaded by capacitance to ground.
6 –IN Inverting Input to the Buffer. A 10 kΩ feedback resistor R1 from the buffer output Pin 5

7 AUDIO +IN Input Audio Signal. The input signal should be ac-coupled (0.1 µF typical) into this pin.
8 AVG CAP Detector Averaging Capacitor. A capacitor, 2.2 µF to 22 µF, to ground from this pin is the

9 NOISE GATE SET Noise Gate Threshold Set Point. A resistor to V+ sets the level below which input signals

10 COMP RATIO SET Compression Ratio Set Pin. A resistor to ground from this pin sets the compression ratio

11 ROTATION SET Rotation Point Set Pin. This is set by a resistor to the positive supply. This resistor together

12 POWER DOWN Power-Down Pin. Connect to ground for normal operation. Connect to positive supply

13 OUTPUT Output Signal

14 V+ Positive Supply, +5 V Nominal

VCA Input Pin. A typical connection is a 10 µF capacitor from the buffer output pin
(Pin 5) to this pin.

Inverting Input to the VCA. This input can be used as a nonground reference for the
audio input signal (see Application Information).

to this input pin, and a resistor R2, from this pin through a 1 µF capacitor to ground gives
gains of 6 dB to 20 dB for R2 = 10 kΩ to 1.1 kΩ.

averaging capacitor for the detector circuit.

are downward expanded. For a 0.7 mV threshold, the resistor value is approximately
380 kΩ. Increasing the resistor value reduces the threshold. See TPC 2.

as shown in Figure 1. TPC 3 gives resistor values for various rotation points.

with the gain adjust pin determines the onset of limiting. A typical value for this resistor is
17 kΩ for a 100 mV “rotation point.” Increasing the resistor value reduces the level at which
limiting occurs. Refer to TPC 7.

for power-down mode.

REV. B

PIN CONFIGURATION

GND

1

GAIN ADJUST

BUF OUT

AUDIO +IN

VCA

VCA

IN

R

–IN

2

3

SSM2166

4

TOP VIEW

(Not to Scale)

5

6

7

–3–

14

V+

13

OUTPUT

12

POWER DOWN

11

ROTATION SET

10

COMP RATIO SET

NOISE GATE SET

9

AVG CAP

8

SSM2166–Typical Performance Characteristics

0

–10

–20

–30

–40

–50

OUTPUT – dBu

–60

–70

–80

–80 0–70 –60 –50 –40 –30 –20 –10

COMP RATIO = 15:1

COMP RATIO = 10:1

COMP RATIO = 5:1

COMP RATIO = 1:1

TA = +25°C
V+ = 5V
VIN = 300mV rms @ 1kHz
R

= 100k⍀

L

NOISE GATE SETTING
ROTATION POINT 300mV rms
GAIN ADJUST (PIN 2) = 1.25k⍀

INPUT – dBu

INPUT – dBu

COMP RATIO = 2:1

TPC 1. Output vs. Input Characteristics

100

TA = +25°C
V+ = 5V

= 100k⍀

R

L

COMPRESSION RATIO = 2:1

10

1

NOISE GATE – mV rms

ROTATION POINT
GAIN ADJUST (PIN 2) = 1.25k⍀

1V rms

550µV rms

20

18

16

14

12

10

GAIN – dB

8

6

4

2

0

0262 4681012 14 16 18 20 22 24

TPC 4. VCA Gain vs. R

5

TA = +25°C
V+ = 5V
COMPRESSION RATIO = 1:1
NOISE GATE SETTING

ROTATION POINT
GAIN ADJUST (PIN 2) = 1.25k⍀

1

THD + N – %

0.1

FREQUENCY = 1kHz

V

IN

TA = +25°C
V+ = 5V

= 100k⍀

R

L

= 100mV rms @ 1kHz

V

IN

NOISE GATE SETTING
ROTATION POINT (PIN 11)
COMPRESSION RATIO = 1:1

GAIN ADJUST RESISTOR – k⍀

(Pin 2 to GND)

GAIN

550␮V rms

1V rms

RL = 10k⍀

RL = 100k⍀

550␮V rms

1V rms

28 30

0.1
0 45050 100 350 400150 200 250 300 500 550 600 650

TPC 2. Noise Gate vs. R

COMPRESSION

RATIO

ROTATION POINT

100mV rms 0

300mV rms 0

1V rms 0

TPC 3. Compression Ratio vs. R

R

– k⍀

GATE

(Pin 9 to V+)

GATE

1:1 2:1 5:1 10:1 15:1

96

12.5

96

12.5

96

12.5

R

– k⍀, TYPICAL

COMP

COMP

215

395

215

395

215

395

(Pin 10 to GND)

0.05

0.01 10.1
INPUT VOLTAGE – V rms

TPC 5. THD + N (%) vs. Input (V rms)

5

TA = +25°C
V+ = 5V
V

= 77.5mV rms @ 1kHz

IN

COMPRESSION RATIO = 1:1
NOISE GATE SETTING

ROTATION POINT

1

GAIN ADJUST (PIN 2) = 1.2k⍀
MEASUREMENT FILTER BW: 22Hz TO 30kHz

THD + N – %

0.1

0.05
20 30k100

550␮V rms

1V rms

1k 10k

FREQUENCY – Hz

TPC 6. THD + N (%) vs. Frequency (Hz)

REV. B–4–

1.0

FREQUENCY – Hz

–10

–80

20 30k100 1k

–20

–30

–40

–50

–60

–70

R

COMP

= 0⍀

R

GAIN

= 1.24k⍀

R

GATE

= 500k⍀

R

ROT

= 1.74k⍀

10k

V+ = 5±1V p-p

V+ = 5±0.5V p-p

PSRR – dB

0.1

ROTATION POINT – V rms

TA = +25°C

V+ = 5V

= 100k⍀

R

L

COMPRESSION RATIO = 1:1
NOISE GATE SETTING

GAIN ADJUST (PIN 2) = 1.25k⍀

550␮V rms

SSM2166

0.01
045510 354015 20 25 30 50 55

TPC 7. Rotation Point vs. R

5␮V

100

90

TA = +25ⴗC

10

0%

COMPRESSION RATIO = 15:1
NOISE BW = 20kHz

R

ROT PT

RESISTOR – k⍀

ROT PT

TPC 8a. Wideband Output Noise

70

G = 60dB

60

50

G = 40dB

40

30

G = 20dB

20

GAIN – dB

10

ROTATION POINT = 1.13V rms

0

NOISE GATE SETTING = 336␮V rms
R

= 40k⍀

COMP

= 400␮V rms

V

–10

IN

–20

1k 1M10k 100k

FREQUENCY – Hz

TPC 8b. GBW Curves vs. VCA Gain

60 65 70 75 80 85 90

(Pin 11 to V+)

1s

TPC 8c. PSRR vs. Frequency

20mV

100

90

TA = +25ⴗC

= 2.2␮F

C

AVG

SYSTEM GAIN = 0dB

= 10k⍀

10

0%

R

L

COMP RATIO = 1:1

TPC 9. Small Signal Transient Response

200mV

100

90

TA = +25ⴗC
C

= 2.2␮F

AVG

SYSTEM GAIN = 0dB
R

10

0%

= 10k⍀

L

COMP RATIO = 1:1

TPC 10. Large Signal Transient Response

10␮s

10␮s

REV. B

–5–