AS3665 datasheet(36/78 Pages) AMSCO

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AS3665

Datasheet, Confidential - D e taile d D e scri pti on Audi o I np ut

AGC (Automatic Gain Control)

The AGC is used to ‘compress’ the input signal and to attenuate very low input amplitude signals (this is performed to

ensure no light output for low signals especially for noisy input signals).

The AGC monitors the input signal amplitude and filters this amplitude with a filter with a short attack time, but a long

decay time (decay time depends on the register agc_ctrl). This amplitude measurement (represented by an integer

value from 0 to 15; the decay time of this measurement is controlled by agc_time) is then used to amplify or attenuate

the input signal with one of the following amplification ratios (output to input ratio) – the curve A, B, or C is selected

depending on the register agc_ctrl:

audio_cmdset

R/W

Modifies the behavior for over/underflow with the

sequencer adder and subtract commands

A over/underflow rolls over

The adder/subtract command saturate

at zero and full scale

audio_buf_on

R/W

Enable audio input buffer

Off

any selection of adc_select possible

adc_select=0 (audio buffer) mandatory

5:3

audio_buf_gain

000b

R/W

Audio input buffer gain setting

000

-12dB

001

-6dB

010

0dB

011

+6dB

100

+12dB

101

+18dB

110

+24dB

111

+30dB

7:6

reserved

00b

R/W

reserved - always set to 00b

1. For audio processing always set audio_cmdset=1

Table 46. AGC gain curves

Input Amplitude

AGC gain

curve A

curve B

curve C

0.0

7.5

5.0

3.5

7.0

4.0

3.0

4.5

3.5

2.5

3.5

3.0

2.0

3.0

2.5

1.5

2.5

1.5

Table 45. Audio_Control Register (Continued)

Addr: 1Ch

Audio_Control Register

Bit

Bit Name

Default Access

Description

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