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DRAGSTER
CONFIDENTIAL
3.2
ADC Gain calibration
To calibrate the gain the best is to use a very stable light source with the possibility to regulate
the light energy. LEDs are recommended. Use the maximum light energy available or tune it so that the
histogram is between 3000DN and 3500DN
Set the sensor to the operating point, especially the gain programmed on the sensor to the
desired setting in your application. Tune the analogue gain on/off ( bit 5 Control 2) and the inverse
ADC gain register.
The histogram should look like this:
Use the 4K_1 SPI and 8K_1 SPI to fine tune the Inverse ADC gain of the individual segments.
Set again a value ±10 of what was set in the Inverse ADC gain of All segments so that we can identify
which segment to tune.
Once the histograms are one over the other the calibration is done and the sensor shows a good
response over all range, just with the remark that the saturation level is not 4096 any more. Because the
on chip offset subtraction is activated, the ADC range is smaller.
As last step, the “End of range” register should be increased so that the ADC covers again a 12
bit range. In the Illustration 1 it's shown that the black level was set around 100DN so this is the value
that is recommended to be increased in the “End of range” register.
DATE:
25/06/09
DRAGSTER Evaluation
Version 0.0.04
PAGE:
5/6
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Figure 3: Initial ADC gain calibration
