MT9M034 datasheet(21/56 Pages) ONSEMI

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MT9M034_DS Rev. G Pub. 4/15 EN

©Semiconductor Components Industries, LLC,2015.

MT9M034: 1/3-Inch CMOS Digital Image Sensor

High Dynamic Range Mode

HDR Specific Exposure Settings

In HDR mode, pixel values are stored in line buffers while waiting for all 3 exposures to

be available for final pixel data combination. There are 42 line buffers used to store inter-

mediate T1 data. Due to this limitation, the maximum coarse integration time possible is

equal to 42*T1/T2 lines.

For example, if R0x3082[3:2] = 2, the sensor is set to have T1/T2 ratio = 16x. Therefore the

maximum number of integration lines is 42*16 = 672 lines. If coarse integration time is

greater than this, the T2 integration time will stay at 42. The sensor will calculate the

ratio internally,enabling the linearization to be performed. If companding is being than

relinearization would still follow the programmed ratio. For example if the T1/T2 ratio

was programmed to 16x but coarse integration was increased beyond 672 than one

would still use the 16x relinearization formulas.

An additional limitation is the maximum number of exposure lines in relation to the

frame_length_lines register. In Linear mode, as described on page 20, maximum

coarse_integration_time = frame_length_lines - 1. However in HDR mode, since the

coarse integration time register controls T1, the max coarse_integration time is

frame_length_lines - 45.

Putting the two criteria listed above together, it can be summarized as follows:

(EQ 3)

In HDR mode, subline integration is not utilized. As such, fine integration time register

changes will have no effect on the image.

There is also a limitation of the minimum number of exposure lines that can be used.

This is summarized in the following formula:

(EQ 4)

Due to limitation on the internal floating point calculation, the exact ratio specified by

the RATIO_T2_T3 (R0x3082[5:4]) may not be achievable.

When using companded output in combination with certain exposure ratios (other than

T1/T2 = 16x and T2/T3 = 16x), digital gain needs to be set to a fixed value. Table below

provides the proper digital gain settings for each T1/T2 and T2/T3 ratio.

Table 7:

Digital Gain Setting for Each T1/T2 and T2/T3Ratio

T1/T2 Ratio

T2/T3 Ratio

Setting for Digital Gain Register

(0x305E Context A or 0x30C4 Context B)

0x02h

0x04h

416

0x08h

0x04h

0x08h

816

0x10h

0x08h

0x10h

Any legal value

maximum coarse_integration_time

minimum 42

T1 T2, frame_length_lines

–







minimum coarse_integration_time

0.5

*T1 T2



 T2 T3





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