OV9121 datasheet(3/30 Pages) ETC1

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Functional Description

Version 1.3, September 15, 2003

Proprietary to OmniVision Technologies

Omni

ision

Image Sensor Array

The OV9625/OV9121 sensor is a 1/2-inch format CMOS

imaging device. The sensor contains 1,359,232 pixels.

Figure 3 shows the active regions of sensor array.

Figure 3 Sensor Array Region

The color filters are Bayer pattern. The primary color

BG/GR array is arranged in line-alternating fashion. Of the

1,359,232 pixels, 1,310,720 are active. The other pixels

are used for black level calibration and interpolation.

The sensor array design is based on a field integration

read-out

system

with

line-by-line

transfer

and

electronic shutter with a synchronous pixel read-out

scheme.

Gain Control

When the column sample/hold circuit has sampled one

row of pixels, the pixel data will shift out one-by-one into

an analog amplifier. The amplifier gain can either be

programmed by the user or controlled by the internal

automatic gain control circuit (AGC). The gain adjustment

range is 0-24 dB.

Channel Balance

The amplified signals are then balanced with a channel

balance block. In this block, Red/Blue channel gain is

increased or decreased to

match

Green channel

luminance level and gamma correction is performed. The

adjustment range is 54 dB. This function can be done

manually by the user or with the internal automatic white

balance controller (AWB).

1035

1034

1033

Column

Dummy

Optical

Black

Dummy

1032

1024

Active

Lines

10-Bit Analog-to-Digital Converter

The balanced signal then will be digitized by the on-chip

10-bit ADC. It can operate at up to 12 MHz, and is fully

synchronous to the pixel clock. The actual conversion rate

is determined by the frame rate.

Black Level Compensation

After the pixel data has been digitized, black level

calibration can be performed before the data is output.

The black level calibration block subtracts the average

signal level of optical black pixels to compensate for the

dark current in the pixel output. Black level calibration can

be disabled by the user.

Windowing

OV9625/OV9121 allows the user to define window size or

region of interest (ROI), as required by the application.

Window size setting (in pixels) ranges from 2 x 4 to

1280 x 1024 (SXGA) or 2 x 2 to 640 x 480 (VGA), and can

be anywhere inside the 1312 x 1036 boundary. Note that

modifying window size or window position does not alter

the frame or pixel rate. The windowing control merely

alters the assertion of the HREF signal to be consistent

with the programmed horizontal and vertical ROI. The

default window size is 1280 x 1024. See Figure 4 and

registers HREFST, HREFEND, VSTRT, VEND, and

COMM for details. The maximum output window size is

1292 columns by 1024 rows.

Note that after writing to register COMH (0x12) to change

the sensor mode, registers related to the sensor’s

cropping window will be reset back to its default value.

Figure 4 Windowing

Column

End

Sensor Array

Boundary

HREF

Column

Display

Window

Column

Start

Row Start

Row End

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