Silicon Imaging , Inc. 2004 Page 5 of 39 Company Confidential
The array has 2048 pixels on a line and 1536 rows, which result in a 4:3 aspect ratio.
The sensor array design is based
on a field integration read-out system with line-by-line transfer and an electronic shutter with a synchronous pixel read-out scheme
(aka. Rolling Shutter Method)
Analog Gain Amplifier & Offset
The imager signal path consists of two stages, a programmable gain stage and a programmable analog offset stage.
The gain settings can be independently adjusted for the colors Green1, Blue, Red, and Green2 and are programmed
through registers. A total programmable gain of 18x is available. The programmable analog offset stage corrects for
analog offset that might be present in the analog signal. The analog offset settings can be independently adjusted for
each color (R/G1/G2/B).
Automatic Black Level Compensation
The automatic black level calibration measures the average value of 256 pixels from two dark rows of the imager for
each of the four colors. The pixels are averaged as if they were light-sensitive and passed through the appropriate
color gain. This average is then digitally filtered over many frames. For each color, the new filtered average is
compared to minimum and a maximum acceptable level. If the average is lower than the minimum acceptable level,
the offset correction voltage for that color is increased. If it is above the maximum level, the level is decreased. The
upper threshold is automatically adjusted upwards whenever an upward shift in the black level from below the
minimum results in a new black level above the maximum. This prevents black level oscillation from below the
minimum to above the maximum. The lower threshold is increased with the maximum gain setting (out of all four
colors), according to Register settings. This prevents clipping of the black level. After changes to the sensor
configuration, large shifts in the black level calibration can result. To quickly adapt to this shift, a rapid sweep of the
black level during the dark-row readout is performed on the first frame after certain changes to the sensor registers.
2.) 10-Bit Digital Sampling System
A 10-Bit Analog-to-digital (A/D) converter samples each pixel value and quantizes it into 1024 levels inside the
sensor. Pixel clock sampling ensures precise measurement of the photonic charge without the jitter and sampling
uncertainty associated with traditional analog video systems, such as RS-170 and CCIR. This produces images
which can deliver improved photometry accuracy and sub-pixel metrology. The use of 10-bit converters versus
traditional 8-bit systems further enhances the image dynamic range. The combination of 10-bit vertical resolution
and pixel clock sampling provide precise sub-pixel measurement accuracy (ex. 1/10 pixel).
