SSM2166 데이터 시트보기 (PDF) - Analog Devices

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SSM2166

Microphone Preamplifier with Variable Compression and Noise Gating

Analog Devices 

Pin #

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Mnemonic

GND

GAIN ADJUST

VCAIN

VCAR

BUF OUT

–IN

AUDIO +IN

AVG CAP

NOISE GATE SET

COMP RATIO SET

ROTATION SET

POWER DOWN

OUTPUT

V+

SSM2166

PIN DESCRIPTION

Function

Ground

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 the compression pin (Pin 10) should be grounded for no com-

pression. 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–3␣ kΩ. For resistor values < 1 kΩ, the VCA can attenu-

ate or mute. Refer to Figure 6.

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 notes).

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

Inverting Input to the Buffer. A 10 kΩ feedback resistor R1 from the buffer output Pin 5 to

this input pin, and a resistor R2, from this pin through a 1 µF to ground gives gains of 6 dB

to 20 dB for R2 = 10 kΩ to 1.1 kΩ.

Input Audio Signal. The input signal should be ac-coupled (0.1 µF typical) into this pin.

Detector Averaging Capacitor. A capacitor, 2.2 µF–22 µF, to ground from this pin is the

averaging capacitor for the detector circuit.

Noise Gate Threshold Set Point. A resistor to V+ sets the level below which input signals are

downward-expanded. For a 0.7 mV threshold, the resistor value is approximately 380 kΩ.

Increasing the resistor value reduces the threshold. See Figure 4.

Compression Ratio Set Pin. A resistor to ground from this pin sets the compression ratio as

shown in Figure 1. Figure 5 gives resistor values for various rotation points.

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

with the gain adjust pin determines the onset of limiting. A typical value for this resistor is

17K for a 100 mV “rotation point.” Increasing the resistor value reduces the level at which

limiting occurs. Refer to Figure 9.

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

power-down mode.

Output Signal.

Positive Supply, +5 V Nominal.

PIN CONFIGURATION

GND 1

14 V+

GAIN ADJUST 2

13 OUTPUT

VCAIN 3

12 POWER DOWN

SSM2166

VCAR 4 TOP VIEW 11 ROTATION SET

BUF OUT 5 (Not to Scale) 10 COMP RATIO SET

–IN 6

9 NOISE GATE SET

AUDIO +IN 7

8 AVG CAP

REV. A

–3–

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