VS6663CC Datasheet, PDF (44/63 Pages) STMicroelectronics – 1.3 megapixel camera module

Video timing
VS6663CC
6.3
6.3.1
Exposure and gain control
VS6663CC 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 VS6663CC through the CCI interface.
The exposure control parameters available on VS6663CC 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 26.
Integration time and analog gain capability registers should be used to determine the
exposure control parameter limits for a given video timing configuration.
Gain model
VS6663CC only supports the single global analog gain mode.The gain is monotonic to
avoid instabilities in the exposure loop VS6663CC has a 16-bit register (0x0204 and
0x0205) to control analog gain.
Figure 18 shows how the analog gain bits are used for VS6663CC.
Figure 18. Analog gain register format
A15 A14 A13 A12 A11 A10 A9 A8
Not used
A7 A6 A5 A4
Coarse gain
A3 A2 A1 A0
Not used Not used
The following generic equation describes VS6663CC gain behavior specified by the analog
gain description registers 0x008A to 0x0093:
gain = c0 ⁄ (m1 ⋅ x + c1)
where:
m₁ = -1
c₀ = 256
c₁ = 256
Table 25 specifies the valid analog gain values for VS6663CC.
Table 25. Analog gain control
Gain value (0x0204/0x0205) Coarse gain code [A7:A4]
0x0000
0000
0x0010
0001
0x0020
0x0030
0010
0011
Coarse analog gain
0.00 dB (x1.00)
0.6 dB (x 1.07)
1.1 dB (x1.14)
1.8 dB (x1.23)
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