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5.5. How to calibrate it?

The final goal of calibration is to get an uniform image with unnoticeable artifacts related to gain or offset mismatches. To achieve a good calibration is mandatory to tune the ADC offset and gain between segments and that can be made in at least i2 necessary steps. One calibration step without light and another with the light, preferentially green (~ 520nm) at about 80% of saturation.

On XK3.5 sensor versions  calibration should be between Even and Odd Pixels 


Odd Pixels : SPI Block CD1 CD2  GH1 GH2

Even Pixels :  SPI Block AB1 AB2  EF1 EF2


Colored versions calibration should be done between the Green Colored channels :

Green Channel :


Black level calibration:

The goal is to get both segment histograms right  one over the other.

Prevent any light of getting to the sensor by switching off the light and placing a black cap over it. Make a "Send All" of the default settings with DragsterComm. First we'll make a rough tuning so that all segments show a histogram over 0. Once this is achieved a fine tuning of the individual black levels has to be made so all histograms overlap and look like a single one. Activate the image histogram. If it is clamped to zero, decrease the black level in "All segments" and send this register. If both segments are far away from zero, increase the black level until one of the histograms start getting close to 0.

After this the histogram should look like this :




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 theinverse ADC gain register.

The histogram should look like this:



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. If the on chip offset subtraction is activated, the ADC range is smaller . 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.


The guide attached contains the basics for the calibration process.


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