SSM2167-1RMZ-R7 - ANALOG DEVICES

Low Voltage Microphone Preamplifier with

Variable Compression and Noise Gating

Data Sheet

SSM2167

Rev. G

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

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

APPLICATIONS

Desktop, portable, or palmtop computers

Telephone conferencing

Communication headsets

Two-way communications

Surveillance systems

Karaoke and DJ mixers

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.

PIN CONFIGURATION

GND

VCA

IN 2

SHUTDOWN

BUF

OUT 4

INPUT

OUTPUT

COMP RE S S ION RATIO

GAT E THRS

AVG CAP

SSM2167

TOP VIEW

(Not t o Scal e)

02628-001

Figure 1. 10-Lead MSOP (RM Suffix)

LIMITING

REGION

LIMITING

THRESHOLD

(ROTATION POINT)

COMPRESSION

REGION 1

DOWNWARD

EXPANSION

THRESHOLD

(NOISE GATE)

DOWNWARD

EXPANSION

REGION

VCA G AIN

OUTPUT (dB)

INP UT (dB)

02628-002

Figure 2. General Input/Output Characteristics

SSM2167 Data Sheet

Rev. G | Page 2 of 12

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

9/11—Rev. F to Rev. G

Changes to Ordering Guide .......................................................... 11

2/11—Rev. E to Rev. F

Added Storage Temperature Range Parameter to Table 2 ........... 4

Deleted Figure 15; Renumbered Figures Sequentially ................. 7

Change to Level Detector Section and Figure 17 ......................... 9

Updated Outline Dimensions ....................................................... 11

6/09—Rev. D to Rev. E

Change to Signal Path Section ........................................................ 8

Updated Outline Dimensions ....................................................... 11

2/09—Rev. C to Rev. D

Changes to Figure 4, Figure 5, Figure 6, and Figure 7 ................. 5

Changes to Ordering Guide .......................................................... 11

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

Data Sheet SSM2167

Rev. G | Page 3 of 12

SPECIFICATIONS

VS = 3.0 V, f = 1 kHz, RL = 100 kΩ, RCOMP = 0 Ω, TA = 25°C, VIN = 100 mV rms, RGATE = 2 kΩ, unless otherwise noted.

Table 1.

Parameter Symbol Test Conditions/Comments Min Typ Max Unit

AUDIO SIGNAL PATH

Voltage Noise Density en 10:1 compression 20 nV/√Hz

Noise 20 kHz bandwidth, VIN = GND −70 dBV

Total Harmonic Distortion + Noise THD + N VIN = 100 mV rms 0.2 %

Input Impedance ZIN 100 kΩ

Output Impedance ZOUT 145 Ω

Load Drive

Minimum resistive load

kΩ

Maximum capacitive load 2 nF

Input Voltage Range 0.4% THD + N 600 mV rms

Output Voltage Range 0.4% THD + N 700 mV rms

Gain Bandwidth Product 1:1 compression, VCA G = 18 dB 1 MHz

CONTROL SECTION

VCA Dynamic Gain Range 40 dB

VCA Fixed Gain 18 dB

Compression Ratio, Minimum 1:1

Compression Ratio, Maximum See Table 4 for RCOMP 10:1

Rotation Point 63 mV rms

Noise Gate Range Maximum threshold −40 dBV

POWER SUPPLY

Supply Voltage VSY 2.5 5.5 V

Supply Current ISY 2.3 5 mA

DC Output Voltage 1.4 V

Power Supply Rejection Ratio PSRR VSY = 2.5 V to 6 V 45 dB

SHUTDOWN

Supply Current ISY Pin 3 = GND 2 8 µA

SSM2167 Data Sheet

Rev. G | Page 4 of 12

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage 6 V

Input Voltage 6 V

Operating Temperature Range −40°C to +85°C

Storage Temperature Range −65°C to +150°C

Junction Temperature 150°C

Lead Temperature (Soldering, 10 sec) 300°C

883 (Human Body) Model 500 V

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.

THERMAL RESISTANCE

θJA is specified for worst-case conditions, that is, θJA is specified

for a device soldered in a 4-layer circuit board for surface-mount

packages.

Table 3.

Package Type

Unit

10-Lead MSOP (RM) 180 35 °C/W

ESD CAUTION

Data Sheet SSM2167

Rev. G | Page 5 of 12

TYPICAL PERFORMANCE CHARACTERISTICS

100

10500 1000 1500 2000 2500 3000 3500

NOISE G ATE (mV rms)

GATE

(Ω)

= 25° C

V+ = 3V

LOAD

= 100k Ω

COM P RE S S ION RAT IO 2: 1

ROTATI ON PO INT = 63mV rms

02628-003

Figure 3. Noise Gate vs. RGATE

0.1

0.0120 100 1k 10k 30k

THD + N ( %)

FRE QUENCY (Hz )

TA = 25° C

V+ = 3V

VIN = 24.5mV rms

COM P RE S S ION RAT IO 1: 1

ROTATI ON PO INT = 63mV rms

NOISE GATE SETTING = 2mV rms

02628-004

Figure 4. THD + N vs. Frequency

–5

–10

–151k 10k 100k 1M 10M

GAIN (dB)

FRE QUENCY (Hz )

= 2mV rms

COMP

= 175kΩ

ROTATI ON PO INT = 63mV rms

NOISE GATE SETTING = 2mV rms

02628-005

Figure 5. GBW Curves vs. VCA Gain

0.1

0.01

0.01 0.1 1

THD + N ( %)

INP UT VOLTAGE (V rms)

= 25° C

V+ = 3V

FRE QUENCY = 1kHz

LOAD

= 100kΩ

COM P RE S S ION RAT IO 1: 1

ROTATI ON PO INT = 63mV rms

NOISE GATE SETTING = 2mV rms

02628-006

Figure 6. THD + N vs. Input Voltage

–80

–70

–60

–50

–40

–30

–20

–10

–80 –70 –60 –50 –40 –30 –20 –10

OUTPUT (dBV)

INP UT (dBV )

COM P RE S S ION RAT IO 10: 1

COM P RE S S ION RAT IO 5: 1

COM P RE S S ION RAT IO 2: 1

COM P RE S S ION RAT IO 1: 1

TA = 25° C

V+ = 3V

RLOAD = 100kΩ

ROTATI ON PO INT = 63mV rms

NOISE GATE SETTING = 2mV rms

02628-007

Figure 7. Output vs. Input Characteristics

–10

–80

–70

–60

–50

–40

–30

–20

10 100 1k 10k 100k

PSRR ( dB)

FRE QUENCY (Hz )

V+ = 3V + 0.1

GATE

= 5kΩ

COMP

= 0Ω

02628-008

Figure 8. PSRR vs. Frequency

SSM2167 Data Sheet

Rev. G | Page 6 of 12

VOLTAGE (50mV/DIV)

TIME (10µs/DIV)

TA = 25° C

CSYS = 10µF

SYSTEM GAIN = 19dB

RLOAD = 100kΩ

COM P RE S S ION RAT IO 1: 1

02628-009

Figure 9. Small Signal Transient Response

VO LTAG E ( 500mV /DIV )

TIME (10µs/DIV)

TA = 25° C

CSYS = 10µF

SYSTEM GAIN = 8.6dB

RLOAD = 100kΩ

COM P RE S S ION RAT IO 1: 1

02628-010

Figure 10. Large Signal Transient Response

VOLTAGE (50mV/DIV)

TIME (10µs/DIV)

TA = 25° C

CSYS = 10µF

SYSTEM GAIN = 8dB

RLOAD = 100kΩ

COM P RE S S ION RAT IO 1: 1

02628-011

Figure 11. Small Signal Transient Response

VO LTAG E ( 200mV /DIV )

TIME (10µs/DIV)

TA = 25° C

CSYS = 10µF

SYSTEM GAIN = 2.6dB

RLOAD = 100kΩ

COM P RE S S ION RAT IO 1: 1

02628-012

Figure 12. Large Signal Transient Response

Data Sheet SSM2167

Rev. G | Page 7 of 12

VO LTAG E ( 100mV /DIV )

TIME (1s/DIV)

–6dBV

–66dBV

–85dBV

02628-013

Figure 13. RMS Level Detector Performance with CAVG = 22 µF

VO LTAG E ( 100mV /DIV )

TIME (500ms/DIV )

–6dBV

–66dBV

–85dBV

02628-014

Figure 14. RMS Level Detector Performance with CAVG = 2.2 µF

SSM2167 Data Sheet

Rev. G | Page 8 of 12

APPLICATIONS INFORMATION

The SSM2167 is a complete microphone signal conditioning

system on a single integrated circuit. Designed primarily for

voice-band applications, this integrated circuit provides ampli-

fication, limiting, variable compression, and noise gate. User

adjustable compression ratio, noise gate threshold, and two

different fixed gains optimize circuit operation for a variety of

applications. The SSM2167 also features a low power shutdown

mode for battery-powered applications.

SSM2167

10µF

GND

500kΩ

SHUTDOWN

INPUT 0.1µF 10µF

+10µF

GND

COMP

GATE

100kΩ

OUTPUT

10µF

02628-016

Figure 15. Typical Application Circuit

VCA+1

CONTROL

0.1µF

10µF

1kΩ 1kΩ

OUTPUT

NOISE G ATE AND

COMPRESSION

SETTINGS

LEVEL

DETECTOR

BUFFER

INPUT

GND

CAVG

10µF

SHUTDOWN RC

RGVDD

VDD

BUFOUT VCAIN

02628-017

Figure 16. Functional Block Diagram

THEORY OF OPERATION

The typical transfer characteristic for the SSM2167 is shown in

Figure 2 where the output level in dB is plotted as a function of

the input level in dB. The dotted line indicates the transfer char-

acteristic for a unity-gain amplifier. For input signals in the range

of VDE (downward expansion) to VRP (rotation point), an “r” dB

change in the input level causes a 1 dB change in the output level.

Here, r is defined as the compression ratio. The compression ratio

may be varied from 1:1 (no compression) to 10:1 via a single

resistor, RCOMP. Input signals above VRP are compressed with a

fixed compression ratio of approximately 10:1. This region of

operation is the limiting region. Varying the compression ratio

has no effect on the limiting region.

The breakpoint between the compression region and the limiting

region is referred to as the limiting threshold or the rotation point.

The term, rotation point, derives from the observation that the

straight line in the compression region rotates about this point on

the input/output characteristic as the compression ratio is changed.

The gain of the system with an input signal level of VRP is the fixed

gain, 18 dBV for the SSM2167, regardless of the compression ratio.

Input signals below VDE are downward expanded; that is, a

−1 dB change in the input signal level causes approximately a

−3 dB change in the output level. As a result, the gain of the

system is small for very small input signal levels, even though

it may be quite large for small input signals above VDE. The

external resistor at Pin 7, RGATE, is used to set the downward

expansion threshold (VDE).

Finally, the SSM2167 provides an active low, CMOS-compatible

digital power-down feature that reduces device supply current

to typically less than 2 µA.

SIGNAL PATH

Figure 16 illustrates the block diagram of the SSM2167. The

audio input signal is processed by the input buffer and then by

the VCA. The input buffer presents an input impedance of

approximately 100 kΩ to the source. A dc voltage of approximately

400 mV is present at INPUT (Pin 5) of the SSM2167, requiring the

use of a blocking capacitor (C1) for ground-referenced sources.

A 0.1 µF capacitor is a good choice for most audio applications.

The input buffer is a unity-gain stable amplifier that can drive

the low impedance input of the VCA and an internal rms detector.

The VCA is a low distortion, variable gain amplifier whose gain

is set by the side-chain control circuitry. An external blocking

capacitor (C2) must be used between the buffer output and the

VCA input. The 1 kΩ impedance between amplifiers determines

the value of this capacitor, which is typically between 4.7 µF and

10 µF. An aluminum electrolytic capacitor is an economical choice.

The VCA amplifies the input signal current flowing through C2

and converts this current to a voltage at the output pin (Pin 9) of

the SSM2167. The net gain from input to output can be as high

as 40 dB, depending on the gain set by the control circuitry.

The output impedance of the SSM2167 is typically less than

145 Ω, and the external load on Pin 9 should be >5 kΩ. The

nominal output dc voltage of the device is approximately 1.4 V;

therefore, a blocking capacitor for grounded loads must be used.

The bandwidth of the SSM2167 is quite wide at all gain settings.

The upper 3 dB point is over 1 MHz at gains as high as 30 dB.

The GBW plots are shown in Figure 5. The lower 3 dB cutoff

frequency of the SSM2167 is set by the input impedance of the

VCA (1 kΩ) and C2. Whereas the noise of the input buffer is

fixed, the input-referred noise of the VCA is a function of gain.

The VCA input noise is designed to be at a minimum when the

gain is at a maximum, thereby maximizing the usable dynamic

range of the part.

Data Sheet SSM2167

Rev. G | Page 9 of 12

LEVEL DETECTOR

The SSM2167 incorporates a full-wave rectifier and a true rms

level detector circuit whose averaging time constant is set by an

external capacitor (CAVG ) connected to the AVG CAP (Pin 6).

For optimal low frequency operation of the level detector down

to 10 Hz, the value of the capacitor should be 2.2 μF. Some experi-

mentation with larger values for CAVG may be necessary to reduce

the effects of excessive low frequency ambient background noise.

The value of the averaging capacitor affects sound quality: too

small a value for this capacitor may cause a pumping effect for

some signals, whereas too large a value can result in slow response

times to signal dynamics. Electrolytic capacitors are recommended

here for lowest cost and should be in the range of 2 μF to 22 μF.

The rms detector filter time constant is approximately given by

10 × CAVG milliseconds where CAVG is in μF. This time constant

controls both the steady state averaging in the rms detector as well

as the release time for compression, that is, the time it takes for

the system gain to increase due to a decrease in input signal. The

attack time, the time it takes for the gain to be reduced because

of a sudden increase in input level, is controlled mainly by internal

circuitry that speeds up the attack for large level changes. In most

cases, this limits overload time to less than 35 ms.

The performance of the rms level detector is illustrated in

Figure 14 for a CAVG of 2.2 μF and Figure 13 for a CAVG of 22 μF.

In Figure 13 and Figure 14, the input signal to the SSM2167

(not shown) is a series of tone bursts in six successive 10 dB

steps. The tone bursts range from −66 dBV (0.5 mV rms) to

−6 dBV (0.5 V rms). As illustrated in these figures, the attack

time of the rms level detector is dependent only on CAVG, but the

release times are linear ramps whose decay times are dependent

on both CAVG and the input signal step size. The rate of release is

approximately 240 dB/s for a CAVG of 2.2 μF, and 12 dB/s for a

CAVG of 22 μF.

CONTROL CIRCUITRY

The output of the rms level detector is a signal proportional to

the log of the true rms value of the buffer output with an added

dc offset. The control circuitry subtracts a dc voltage from this

signal, scales it, and sends the result to the VCA to control the

gain. The gain control of the VCA is logarithmic—a linear change

in control signal causes a dB change in gain. It is this control

law that allows linear processing of the log rms signal to provide

the flat compression characteristic on the input/output charac-

teristic shown in Figure 2.

OUTPUT ( dB)

INPUT (dB) VRP

VDE

10:1

5:1

2:1

1:1

VCA GAIN

02628-018

Figure 17. Effect of Varying the Compression Ratio

SETTING THE COMPRESSION RATIO

Changing the scaling of the control signal fed to the VCA causes

a change in the circuit compression ratio, r. This effect is shown

in Figure 17. Connecting a resistor (RCOMP) between Pin 8 and

VDD sets the compression ratio. Lowering RCOMP gives smaller

compression ratios as indicated in Table 4. AGC performance is

achieved with compression ratios between 2:1 and 10:1, and is

dependent on the application. Shorting RCOMP disables the AGC

function, setting the compression equal to 1:1. If using a compres-

sion resistor, using a value greater than 5 kΩ is recommended.

If a value lower than 5 kΩ is used, the device may interpret this

as a short, 0 Ω.

Table 4. Setting Compression Ratio

Compression Ratio Value of RCOMP

1:1 0 Ω (short to V+)

2:1 15 kΩ

3:1 35 kΩ

5:1 75 kΩ

10:1 175 kΩ

SSM2167 Data Sheet

Rev. G | Page 10 of 12

SETTING THE NOISE GATE THRESHOLD

(DOWNWARD EXPANSION)

The noise gate threshold is a programmable point using an external

resistor (RGATE) that is connected between Pin 7 (GATE THRS)

and VDD. The downward expansion threshold may be set between

−40 dBV and −55 dBV, as shown in Table 5. The downward

expansion threshold is inversely proportional to the value of this

resistance: setting this resistance to 0 Ω sets the threshold at

approximately 10 mV rms (−40 dBV), whereas a 5 kΩ resistance

sets the threshold at approximately 1 mV rms (−55 dBV). This

relationship is illustrated in Figure 18. It is not recommended

to use more than 5 kΩ for the RGATE resistor because the noise

floor of the SSM2167 prevents the noise gate from being

lowered further without causing problems.

Table 5. Setting Noise Gate Threshold

Noise Gate (dBV) Value of RGATE

−40 0 Ω (short to V+)

−48 1 kΩ

−54 2 kΩ

−55 5 kΩ

OUTPUT ( dB)

INPUT (dB)

DE1

DE3

DE2

r:1

VCA GAIN

2628-019

Figure 18. Effects of Varying the Downward

Expansion (Noise Gate) Threshold

ROTATION POINT (LIMITING)

Input signals above a particular level, the rotation point, are

attenuated (limited) by internal circuitry. This feature allows the

SSM2167 to limit the maximum output, preventing clipping of

the following stage, such as a codec or ADC. The rotation point

for the SSM2167 is set internally to −24 dBV (63 mV rms).

SHUTDOWN FEATURE

The supply current of the SSM2167 can be reduced to under

10 μA by applying an active low, 0 V CMOS-compatible input

to the SHUTDOWN pin (Pin 3) of the SSM2167. In this state,

the input and output circuitry of the SSM2167 assumes a high

impedance state; as such, the potentials at the input pin and the

output pin are determined by the external circuitry connected

to the SSM2167. The SSM2167 takes approximately 200 ms to

settle from a shutdown to power-on command. For power-on to

shutdown, the SSM2167 requires more time, typically less than

1 sec. Cycling the power supply to the SSM2167 can result in

quicker settling times: the off-to-on settling time of the SSM2167 is

less than 200 ms, whereas the on-to-off settling time is less than

1 ms. The SSM2167 shutdown current is related to both temper-

ature and voltage.

PCB LAYOUT CONSIDERATIONS

Because the SSM2167 is capable of wide bandwidth operation

and can be configured for as much as 60 dB of gain, special care

must be exercised in the layout of the PCB that contains the IC

and its associated components. The following applications hints

should be considered for the PCB.

The layout should minimize possible capacitive feedback from

the output of the SSM2167 back to its input. Do not run input

and output traces adjacent to each other.

A single-point (star) ground implementation is recommended

in addition to maintaining short lead lengths and PCB runs. In

applications where an analog ground and a digital ground are

available, the SSM2167 and its surrounding circuitry should be

connected to the analog ground of the system. As a result of

these recommendations, wire-wrap board connections and

grounding implementations are to be explicitly avoided.

Data Sheet SSM2167

Rev. G | Page 11 of 12

OUTLINE DIMENSIONS

COMPLIANT TO JEDEC STANDARDS MO-187-BA

091709-A

6°

0°

0.70

0.55

0.40

0.50 BSC

0.30

0.15

1.10 MAX

3.10

3.00

2.90

COPLANARITY

0.10

0.23

0.13

3.10

3.00

2.90

5.15

4.90

4.65

PIN 1

IDENTIFIER

15° MAX

0.95

0.85

0.75

0.15

0.05

Figure 19. 10-Lead Mini Small Outline Package [MSOP]

(RM-10)

Dimensions shown in millimeters

ORDERING GUIDE

Model1 Temperature Range Package Description Package Option Branding

SSM2167-1RMZ-REEL −40°C to +85°C 10-Lead MSOP RM-10 B11

SSM2167-1RMZ-R7 −40°C to +85°C 10-Lead MSOP RM-10 B11

SSM2167Z-EVAL Evaluation Board

1 Z = RoHS Compliant Part, # denotes RoHS compliant product may be top or bottom marked.

SSM2167 Data Sheet

Rev. G | Page 12 of 12

NOTES

registered trademarks are the property of their respective owners.

D02628-0-9/11(G)