SSM2166 Analog Devices, SSM2166 Datasheet

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SSM2166

Manufacturer Part Number
SSM2166
Description
Microphone Preamplifier with Variable Compression & Noise Gating
Manufacturer
Analog Devices
Datasheet

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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 set-
ting the SSM2166 can be programmed with a fixed gain of up to
*Patents pending.
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.
REV. A
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 ( 1 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
+
R2 = 10k
1 F
AUDIO
Figure 2. Functional Block Diagram and Typical Speech Application
+IN
0.1 F
R1 = 10k
POWER
7
DOWN
6
SSM2166
12
BUFFER
GND
1
BUF
Variable Compression and Noise Gating
DETECTOR
OUT
5
LEVEL
AVG
CAP
10 F
VCA
+
22 F
3
IN
8
4
1k
20 dB; this gain is in addition to the variable gain in other com-
pression 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 opti-
mized 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 14-lead SOIC and P-DIP packages,
and guaranteed for operation over the extended industrial tempera-
ture range of –40 C to +85 C. For similar features/performance
in an 8-lead package, please refer to the SSM2165.
Figure 1. SSM2166 Compression and Gating Characteris-
tics with 10 dB of Fixed Gain (The Gain Adjust Pin Can Be
Used to Vary This Fixed Gain Amount)
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
+
10 F
1k
VCA
+
25k
Microphone Preamplifier with
10
VCA
R
CONTROL
*
COMPRESSION
RATIO
SET
–10
–20
–30
–40
–50
–60
10
0
–70
V+
14
–60
RATIO = 10:1
*
OPTIONAL
13
11
2
9
V
RATIO = 1:1
OUT
RATIO = 2:1
VCA GAIN
World Wide Web Site: http://www.analog.com
NOISE GATE
ROTATION
POINT SET
2.3k
–50
ADJ
500k
17k
SET
–40
INPUT – dBu
–30
V+
© Analog Devices, Inc., 1999
SSM2166*
–20
–10
0

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SSM2166 Summary of contents

Page 1

... In the 1:1 compression set- ting the SSM2166 can be programmed with a fixed gain 10k AUDIO +IN ...

Page 2

... 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 ...

Page 3

... Output Signal. Positive Supply Nominal. PIN CONFIGURATION GND GAIN ADJUST 2 13 OUTPUT 12 VCA 3 POWER DOWN IN SSM2166 4 11 VCA ROTATION SET R TOP VIEW (Not to Scale) BUF OUT 5 10 COMP RATIO SET 6 NOISE GATE SET –IN 9 AVG CAP AUDIO + –3– SSM2166 ...

Page 4

... SSM2166 0 COMP RATIO = 15:1 COMP RATIO = 10:1 COMP RATIO = 5:1 –10 –20 –30 – +25 A – 300mV rms @ 1kHz IN – 100k L NOISE GATE SETTING ROTATION POINT –70 COMP RATIO = 1:1 GAIN ADJUST (PIN 2) = 1.25k –80 –80 –70 –60 –50 –40 INPUT – dBu INPUT – ...

Page 5

... V rms –40 –50 –60 –70 – (Pin 11 to V+) 1s Figure 11. Small Signal Transient Response 100k 1M Figure 12. Large Signal Transient Response –5– SSM2166 COMP R = 1.24k GAIN R = 500k GATE R = 1.74k ROT V+ = 5±1V p 5±0.5V p-p 100 1k 10k FREQUENCY – ...

Page 6

... The gain of the VCA at the rotation point is set by the value of a resistor connected between Pin 2 and GND, R tionship between the VCA gain and R The AGC range of the SSM2166 can be as high as 60 dB. The is fixed RP VCA ...

Page 7

... Figure 14. Functional Block Diagram and Typical Application bandwidth is unaffected). The GBW plots are shown in Figure 10b. The lower 3 dB cutoff frequency of the SSM2166 is set by the input impedance of the VCA ( and C6. While the noise of the input buffer is fixed, the input referred noise of the VCA is a function of gain ...

Page 8

... COMP Figure 17. Effect of Varying the Rotation Point VCA Gain Setting and Muting. The maximum gain of the SSM2166 is set by the GAIN ADJUST pin (Pin 2) via R This resistor, with a range between 1 k and will cause the nominal VCA gain to vary from approximately 20 dB, respectively. To set the VCA gain to its maximum can also be achieved by leaving the GAIN ADJUST pin in an OPEN condition (no connect) ...

Page 9

... SSM2166 using a resistor, R connected between the positive supply and the NOISE GATE SET pin (Pin 9) of the SSM2166. The effect of varying this threshold is shown in Figure 20. The downward expansion threshold may be set between 300 V rms and 20 mV rms by varying the resistance value between Pin 9 and the supply volt- age ...

Page 10

... As a design aid, the layouts for the topside silkscreen, topside and backside metallization layers are shown in Figures 23a, b, and c. Although not shown to scale, the finished dimen- sion of the evaluation board is 3.5 inches by 3.5 inches, and comes complete with pin sockets and a sample of the SSM2166 0.1 F ...

Page 11

... BUF pin (Pin 5) of the SSM2166. OUT The output stage of the SSM2166 is capable of driving > rms (3 V p-p) into > loads, and is externally available through an RCA phono jack provided on the board. If the out- put of the SSM2166 is required to drive a lower load resistance – ...

Page 12

... GENERATOR VOLTMETER STEP 1. Configure the Buffer The SSM2166 has an input buffer that may be used when the overall gain required exceeds 20 dB, the maximum user- 1-15 mV selectable gain of the VCA. In our example, the desired output is 500 mV for an input around 15 mV, requiring a total gain of 500 ...

Page 13

... STEP 8. Listening At this time, you may want to connect an electret microphone to the SSM2166, and listen to the results. Be sure to include the proper power for the microphone’s internal FET (usually + through a 2.2 k resistor). Experiment with the settings to hear how the results change. Varying the averaging capacitor, C4, changes the attack and decay times, which are best determined empirically ...

Page 14

... SSM2166 SSM2166 Demo Board Parts List R1 10k* R2 10k R3 50k Pot 100k Pot R7 1M Pot R10 20k Pot R11 330 R12 100k 2.2– IC1 SSM2166P IC2 OP113FP S1 SPST J1 1/8" Mini Phone Plug J2 RCA Female *Note: R values values in F. Figure 28. Evaluation Board Parts List ...

Page 15

... SEATING PLANE –15– SSM2166 14-Lead Narrow-Body SOIC (SO-14) 0.3444 (8.75) 0.3367 (8.55 0.2440 (6.20 0.2284 (5.80) 0.0688 (1.75) PIN 1 0.0196 (0.50) x 45° ...

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