VS6663CB datasheet(45/64 Pages) STMICROELECTRONICS

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VS6663CB

Video timing

6.3

Exposure and gain control

VS6663CB does not contain any form of automatic exposure control. To produce a correctly

exposed image the integration period and analog gain for the pixels must be calculated by

an exposure control algorithm implemented externally. The parameters are then written to

the VS6663CB through the CCI interface.

The exposure control parameters available on VS6663CB are:

•

fine integration time

•

coarse integration time

•

analog gain

•

digital gain

The exposure control parameter registers are defined in Section 4.2.6: Integration time and

gain registers [0x0200 to 0x02FF] on page 27.

Integration time and analog gain capability registers should be used to determine the

exposure control parameter limits for a given video timing configuration.

6.3.1

Gain model

VS6663CB only supports the single global analog gain mode.The gain is monotonic to avoid

instabilities in the exposure loop VS6663CB has a 16-bit register (0x0204 and 0x0205) to

control analog gain.

Figure 18 shows how the analog gain bits are used for VS6663CB.

Figure 18. Analog gain register format

The following generic equation describes VS6663CB gain behavior specified by the analog

gain description registers 0x008A to 0x0093:

where:

m1 = -1

c0 = 256

c1 = 256

Table 25 specifies the valid analog gain values for VS6663CB.

Table 25. Analog gain control

Gain value (0x0204/0x0205)

Coarse gain code [A7:A4]

Coarse analog gain

0x0000

0000

0.00 dB (x1.00)

0x0010

0001

0.6 dB (x 1.07)

0x0020

0010

1.1 dB (x1.14)

0x0030

0011

1.8 dB (x1.23)

A15 A14 A13 A12 A11 A10

Coarse gain

Not used

gain

( 1x

⋅

⁄

)

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