MT9V024 datasheet(37/62 Pages) ONSEMI

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MT9V024_DSRev. G Pub. 4/15 EN

©Semiconductor Components Industries, LLC, 2015.

MT9V024: 1/3-Inch Wide-VGA Digital Image Sensor

Feature Description

Black Level Calibration

Black level calibration is controlled by:

•Frame Dark Average: R0x42

• Dark Average Thresholds: R0x46

• Black Level Calibration Control: R0x47

• Black Level Calibration Value: R0x48

• Black Level Calibration Value Step Size: R0x4C

The MT9V024 has automatic black level calibration on-chip, and if enabled, its result

may be used in the offset correction shown in Figure 28.

Figure 28:

Black Level Calibration Flow Chart

The automatic black level calibration measures the average value of pixels from 2 dark

rows (1 dark row if row bin 4 is enabled) of the chip. (The pixels are averaged as if they

were light-sensitive and passed through the appropriate gain.)

This row average is then digitally low-pass filtered over many frames (R0x47, bits 7:5) to

remove temporal noise and random instabilities associated with this measurement.

Then, the new filtered average is compared to a minimum acceptable level, low

threshold, and a maximum acceptable level, high threshold.

If the average is lower than the minimum acceptable level, the offset correction voltage

is increased by a programmable offset LSB in R0x4C. (Default step size is 2 LSB Offset = 1

ADC LSB at analog gain = 1X.)

If it is above the maximum level, the offset correction voltage is decreased by 2 LSB

(default).

To avoid oscillation of the black level from below to above, the region the thresholds

should be programmed so the difference is at least two times the offset DAC step size.

In normal operation, the black level calibration value/offset correction value is calcu-

lated at the beginning of each frame and can be read through the two-wire serial inter-

face from R0x48. This register is an 8-bit signed two’s complement value.

However, if R0x47, bit 0 is set to “1,” the calibration value in R0x48 is used rather than the

automatic black level calculation result. This feature can be used in conjunction with the

“show dark rows” feature (R0x0D[6]) if using an external black level calibration circuit.

Pixel Output

(reset minus signal)

Offset Correction

Voltage (R0x48 or

result of BLC)

10 (12) bit ADC

ADC Data

(9:0)

Gain Selection

(R0x35 or R0x36 or

result of AGC)

VREF

(R0x2C)

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