PixArt Imaging Inc.

PAC7312

VGA PC Camera Single-Chip with Audio

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PixArt Imaging Inc.

V1.5 Oct. 2005

3

. Function Description

3.1Analog DataPath

The PixArt VGA sensor is a 1/4inch CMOS imaging sensor with 644x488 physical pixels. The active

region of sensor array is 644x484. The sensor array is cover with Bayer pattern color filters and micro lens.

After a programmable exposure time, the image is sampled first with CDS (Correlated Double Sampling) block

to improve S/N ration and reduce fixed pattern noise.

Three analog gain stages are implemented before signal transferred by the 10bit ADC. The front gain stage

(FG) can be programmed to fit the saturation level of sensor to the full-range input of ADC. The programmable

color gain stage (CG) is used to balance the luminance response difference between B/G/R. The global gain

stage (GG) is programmed to adapt the gain to the image luminance.

The fine gained signal will be digitized by the on-chip 10bit ADC. After the image data has been digitized,

further alteration to the signal can be applied before the data is output.

The gain stage can be set by digital register, please refer to the following equation to get the mapping gain.

Front Gain =

2 + (n/4),

n = 0, 1, 2, …7

Color Gain =

1 + (m/16),

m= 0, 1, 2, …15

Global Gain =

1 + (q/16),

q = 0, 1, 2, …15