VV6501 datasheet(20/60 Pages) STMICROELECTRONICS

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Functional Description

VV6501

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3.1.11 Exposure/gain control

The sensor does not contain any form of automatic exposure or gain control. To produce a correctly

exposed image, exposure and gain values must be calculated externally and written to the sensor

via the serial interface.

Exposure calculation

The exposure time for a pixel and the ADC range (therefore the gain) are programmable via the

serial interface. The explanation below assumes that the gain and exposure values are updated

together as part of a 5 byte serial interface auto-increment sequence.

Exposure time combines coarse, fine exposure, pixel rate also related to frame and line lengths, all

defined in

Table 6.

Example of exposure calculation in default VGA video mode

coarse exposure = 522

fine exposure = 762

Input clock frequency - Fclkin = 24MHz,

Pixel period = 2/(24 x 106) = 8.33 x10-8 s

Calculation: exposure time = 8.33 x10-8 x [(522 x 762) +762] = 33.2 ms

101X

110X

111X

Table 6: Definitions related to exposure

Frame length

Number of lines per frame [default=524]

The frame length may be increased to 1023 by writing to the frame length register.

Line length

Number of pixels in a line [default = 762]

The line length may be increased to 1023 by writing to the line length register.

Exposure

The pixel exposure time is determined by the course and fine exposure values

Coarse exposure

value

The number of lines a pixel exposes for.

Limited by frame length.

Coarse exposure value is in the range [0 - (frame length -2)].

Fine exposure value

Number of additional pixel periods a pixel exposes for.

Limited by line length.

Fine exposure value is in the range [11 - (line length)].

Pixel period

Determined by the input clock frequency (Fclkin) and user clk_div setting.

PixPeriod=(2*N)/Fclkin where N = clock divider ratio

Exposure time

PixPeriod x [(Coarsenum_lines x Line_Lengthnum_pixels) + Finepixels]

Table 5: User programmable clock divider values

clk_div[3:0]

divide by

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