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NJW1165

AUDIO PROCESSOR

Japan Radio Corporation  

NJW1165

s APPLICATION NOTE

1. AGC (Auto Gain Control) Circuit

AGC circuit adjusts the input signal level with Boost/Attenuate circuit. AGC boost the low input signal level

and attenuate high input signal level automatically.

The AGC flat levels (150mV, 300mV, 400mV and 540mV) are selectable via I2C bus. (Refer to the following

figure.)

AGC Control

V+=9V, Vin(Ach+Bch), f=1kHz, Vo(Ach)OUTPUT

Rg=600Ω, Ta=25oC

1

540mV

0.1

AGC ON

400mV

300mV

150mV

0.01

AGC OFF

Attack-Recovery

0.001

0.001

0.01

0.1

1

Input Voltage [Vrms]

Ra=4kΩ

Ir=0.5µA

9pin

Ca

Rb=8kΩ

11pin

12pin

Cb

Smoothing circuit of Attenuate

Smoothing circuit of Boost

Attack and recovery time in the attenuation processing depends on external part Ca, and it in the boost

processing depends on external part Cb. They become longer as the capacity bigger and become shorter as

it gets smaller. (Recommendation value: Ca=1µF, Cb=4.7µF)

Reducing the capacity of Ca may cause the distortion. As for Cb, since it serves as the click noise

prevention, reducing the capacity may cause the click noise upon volume changing.

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