MT9P001 Datasheet, PDF (35/48 Pages) ON Semiconductor – CMOS Digital Image Sensor

MT9P001: 1/2.5-Inch 5Mp Digital Image Sensor
Features
analog multiplier is specified by Green1_Analog_Multiplier, Red_Analog_Multiplier,
Blue_Analog_Multiplier, and Green2_Analog_Multiplier. These combine to form the
analog gain for a given color C as shown in this equation:
AG_C = (1 + C_Analog_Multiplier) × (C_Analog_Gain / 8)
The gain component can range from 0 to 7.875 in steps of 0.125, and the multiplier
component can be either 0 or 1 (resulting in a multiplier of 1 or 2). However, it is best to
keep the “gain” component between 1 and 4 for the best noise performance, and use the
multiplier for gains between 4 and 8.
Digital Gain
Offset
The digital gain is specified independently for each color channel in steps of 0.125. It is
controlled by the register fields Green1_Digital_Gain, Red_Digital_Gain, Blue_Digi-
tal_Gain, and Green2_Digital_Gain. The digital gain for a color C is given by:
DG_C = 1 + (C_Digital_Gain / 8)
The MT9P001 sensor can apply an offset or shift to the image data in a number of ways.
An analog offset can be applied on a color-wise basis to the pixel voltage as it enters the
ADC. This makes it possible to adjust for offset introduced in the pixel sampling and
gain stages to be removed, centering the resulting voltage swing in the ADC's range. This
offset can be automatically determined by the sensor using the automatic black level
calibration (BLC) circuit, or it can be set manually by the user. It is a fairly coarse adjust-
ment, with adjustment step sizes of 4 to 8 LSBs.
Digital offset is also added on a color-wise and line-wise basis to fine tune the black level
of the output image. This offset is based on an average black level taken from each row's
dark columns, and is automatically determined by the digital row-wise black level cali-
bration (RBLC) circuit. If the RBLC circuit is not used, a user-defined offset can be
applied instead. This offset has a resolution of 1 LSB.
A digital offset is added on a color-wise basis to account for channel offsets that can be
introduced due to "even" and "odd" pixels of the same color going through a slightly
different ADC chain. This offset is automatically determined based on dark row data, but
it can also be manually set.
Analog Black Level Calibration
The MT9P001 black level calibration circuitry provides a feedback control system since
adjustments to the analog offset are imprecise by nature. The goal is that within the dark
row region of any supported output image size, the offset should have been adjusted
such that the average black level falls within the specified target thresholds.
The analog offsets normally need a major adjustment only when leaving the Reset state
or when there has been a change to a color's analog gain. Factors like shutter width and
temperature have lower-order impact, and generally only require a minor adjustment to
the analog offsets. The MT9P001 has various calibration modes to keep the system stable
while still supporting the need for rapid offset adjustments when necessary.
The two basic steps of black level calibration are:
1. Take a sample.
2. If necessary, adjust the analog offset.
MT9P001_DS Rev. L 4/15 EN
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