Omnivision CameraChip OV9650, Implementation Manual

Page: 17 / 56

Timing Generator
Version 1.1, December 7, 2004 Proprietary to OmniVision Technologies 17
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AEC Convergence Limits
Table 3-3 lists the registers used for setting AEC convergence limits.
As shown in Figure 3-2 , the AEC/AGC convergence uses two regions, the inner stable operating
region and the outer Control Zone, which defines the convergence step size change as follows:
• Outside Control Zone
Exposure time increase: 2
×
(AEC[15:0])
Exposure time decrease: (AEC[15:0]) / 2
• Inside Control Zone
Exposure time increase: (AEC[15:0]) / 16
Exposure time decrease: (AEC[15:0]) / 16
Once the current value is inside the stable operating region, the AEC/AGC value has converged.
Figure 3-2 Desired Convergence
Control Zone Upper Limit: { VPT [7:4] (0x26) (MSB), 4’b0000 (LSB)}
Control Zone Lower Limit: { VPT [3:0] (0x26) (MSB), 4’b0000 (LSB)}
Stable Operating Region Upper Limit: AEW [7:0] (0x24)
Stable Operating Region Lower Limit: AEB [7:0] (0x25)
Table 3-3. AEC Convergence Limits
Function Register Address
Control Zone – Upper Limit high nibble VPT [7:4] 0x26
Control Zone – Lower Limit high nibble VPT [3:0] 0x26
Stable Operating Region – Upper Limit AEW [7:0] 0x24
Stable Operating Region – Lower Limit AEB [7:0] 0x25
Step Size Limit COM8 [6] 0x13
Control Zone Stable Operating Region
Desired
Convergence