Silicon Imaging , Inc. 2004 Page 23 of 39 Company Confidential
Signal Path &
Black Level Controls
The SI-3300 analog signal path consists of the pixel array, the column sample and hold (S/H) circuitry, the
programmable gain stage, the analog offset correction and the analog-to-digital converter (ADC). The reset and
signal voltages from the pixel are sampled onto the column sample and hold circuitry on a row-wise basis. After
signal sampling is complete, the differential signal (reset-signal) is transferred to the programmable gain stage.
After the gain stage, the differential signal goes through the analog offset correction circuitry. The user can decide if
a positive or negative offset or no offset needs to be added to the differential signal. The signal is then sampled onto
the sample and hold circuitry of the ADC before being digitized.
Register
Name
Default
Description
0x62
Auto Black Level Control
X0000
0 0= Auto Black Calc, 1= Use Manual Black Levels (x60, x61, x63, x64)
1 0 = Enable Correction, 1 = Disable Correction Voltage
0x60, 0x61
0x63, 0x64
Manual Black Offsets
Green1,
Green2,
Red,
Blue
0x0020
Two's compliment representation of analog offset correction value.
Bit[8] =1 causes the analog offset correction to be negative. Bit[7-0] = value
Green1 (x60),
Green2 (x61),
Red (x63),
Blue (x64)
6-0 Low Coarse Threshold. Max =less than High Target Threshold.
0x5D
Auto Black
Coarse Thresholds
0x2D13
14-8 High Coarse Threshold. Min = greater than Low Target Threshold.
If the average black value for a color is higher than this value or lower than
Low Coarse Threshold, the coarse mode will be activated (if enabled).
Once the black level is in range the fine method will be used.
6-0 Thresh_lo: default = 29 Lower threshold for black level in ADC LSBs
0x5F
Auto Black
Fine Thresholds
0x231D
14-8 Thresh_hi: default = 35. Upper threshold for black level in ADC LSB.
When the black value is within these thresholds, it is considered on target.
0x49
Black Level Target
0x00A8
Target Black Level (Bits 15~0). Digital offset will be applied such that the
average black level of a frame in a resulting image equals the value of this
register. This adjustment happens after black level calibration.
Auto Black Level Thresholds
(Registers: 0x5D & 0x5F)
The digitized black level of the camera will potentially vary with temperature or gain setting changes. The SI-3300
allows the user the flexibility of automatic black level calibration or manual black level control. In automatic mode,
the black level will be adjusted to be within the high and low thresholds set in Reg5D and 5F. The final black level
digital output can be further adjusted by Reg49.
