WM8235 datasheet(49/154 Pages) CIRRUS

49 / 154 page

WM8235

Rev 4.6

AUTOMATIC GAIN CONTROL (AGC)

The Automatic Gain Control (AGC) function is to adjust the gain to an appropriate level for a range of

input signal levels. The AGC function is enabled by AGC_EN register set to 1. The gain control

process has three stages as shown in Figure 32 below:

AGAIN

PEAK

(read only)

Peak

(1)

Peak

(2)

DGAIN

AGAIN

DGAIN

Again(N)

DGAIN(x1)

AGC_EN

PEAK_DET

(internal)

Status

of AGC

N line = AGC_APD[2:0]

M line = AGC_DPD[2:0]

1line

Gain caluculation

FLAG_AGC

(read only)

Dgain(M)

SPI

Cleared peak

value

First rising edge of

PEAK_DET after

AGE_EN=0

Disable

Peak detection for analogue gain

Peak detection for digital gain

Applied calibrated gain

Disable

Peak

(N)

Peak

(1)

Peak

(2)

Peak

(M)

Figure 32 Automatic Gain Control

Analogue Gain Calibration

The analogue gain keep the previous setting (AGAIN) and the digital gain set to x1

(DGAIN=12’d2048) automatically. During the PEAK_DET=high period, peak detection is executed

then calculate an appropriate analogue gain (Again(N)) while PEAK_DET=low period. This period

needs 200 pixels at least. The number of peak detection cycle is selectable by AGC_APD register.

Minimum cycle is 0 (In this case the analogue gain calibration is not executed), Maximum cycle is 7

lines. The peak value is cleared when analogue peak detection finished.

Digital Gain Calibration

The analogue gain is set to the calibrated value (Again(N)), and the digital gain is set to x1

(DGAIN=12’d2048) automatically. Then peak detection and digital gain calibration are executed. Also,

the number of peak detection line is selectable by AGC_DPD register. Minimum cycle is 0 (In this

case the digital gain calibration is not executed), Maximum cycle is 7 lines.

Applied Calibrated Analogue and Digital Gain

The analogue and digital gain are holding calibrated value until AGC_EN register set to 0.

Again(N) = AGC_TARGETINP* / peak(n) x AGAIN

Dgain(M) = (AGC_TARGETINP*

– TARGETINP*) / (peak(M) – TARGETINP*)

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