Awaiba Dragster V3-8K-3.5 Calibration Manual

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DRAGSTER

CONFIDENTIAL

DRAGSTER

Calibration

Revision : 0.0.04

Date : 25/06/09

Contact :

AWAIBA GmbH

Am Wegfeld 30

90427 Nurnberg

Germany

www.awaiba.com

1 Introduction

DATE: 25/06/09

DRAGSTER Evaluation

Version 0.0.04

PAGE: 1/6

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DRAGSTER

CONFIDENTIAL

This document gives a brief explanation about how to configure the Dragster sensors in order to

reduce the effects of the mismatch between pixel segments and to make the light response

linear for all sensor.

2 Setup

For this calibration the system will include an Eval board configured as medium camera link, a

Dragster sensor V3-8K-3.5, the communication software DragsterComm and the frame grabber Me4

from SiliconSoftware.

Although this calibration is made with a V3, the process is similar to the other versions.

3 Calibration

The final goal of the calibration is to tune the ADC offset and gain error between segments so

than we get a uniform image out of the sensor. For that 2 steps are necessary. One calibration step

without light and another with the light, preferentially green (~ 520nm) at about 80% of saturation.

The image histogram is the guide over all the calibration process.

Before starting it's recommended to reset the sensor and sending the default values with the

DragsterComm. Check that from pixels 4 to 7 there are the black and white reference pixels and after

that only black pixels are present until the 63

rd

.

3.1 Black level calibration

The goal is to get both segment histograms right over 0 and one over the other.

DATE: 25/06/09

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Figure 1: Image in light with default settings and no calibration.

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DRAGSTER

CONFIDENTIAL

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:

Now the fine tuning has to adjust the higher histogram to go over the other. For this we need to

identify which of them is the higher one. By setting a black level ± 10 of what was set in the Black

level All Segments it should be easy to identify it.

Note: To set the black level of individual segments use only the 4K_1 SPI and 8K_1 SPI.

After the fine calibration, the black level should look like this:

DATE: 25/06/09

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Figure 2: Initial black level

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DRAGSTER

CONFIDENTIAL

After this we should make the offset correction in order to use again all the ADC range,

otherwise the first DN are wasted for the black signal and we'll never get pixels with values under what

was set. This should be made on chip using the Control 2 and Control 1 register. The next sequence is

the most adequate and although others might also work these steps are the safest.

Using the “Send” buttons of the individual registers, follow this sequence:

1. Start by making sure that in Control 1 "Subtract offset" bit is 0 and "Update request" to 1. Click

“Send”

2. Set the sensor to dark condition and adjust the black level to the smallest output value over 0,

like described in this document. Avoid any pixel value of 4DN,i.e., the lowest ADC output

value.

3. Set in Control 2 "Write Offset" bit to 1. Click “Send”.

4. Using Control 1 send the "Update request" on 1. Click “Send”. The image will ALWAYS

freeze, i.e, is not light sensitive, and the new acquired values are written to the internal offset

register. Looking at the histogram, if it did not freeze, the sequence has to be restarted.

5. Set in Control 2 "Write Offset" bit to 0. Then “Send”.

6. Set in Control 1 "Subtract offset" bit to 1 and "Update request" to 0. Click “Send”.

7. Set again in Control 1 the "Update request" bit to 1 and click “Send”.

Now the dark image will be subtracted on chip from the illuminated image.

When turning "Subtract offset" bit in Control 1 to 0 the stored offset image is lost and needs to

be reacquired with the same step sequence.

DATE: 25/06/09

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Version 0.0.04

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Illustration 1: Black level calibrated

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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

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Figure 3: Initial ADC gain calibration

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DRAGSTER

CONFIDENTIAL

DATE: 25/06/09

DRAGSTER Evaluation

Version 0.0.04

PAGE: 6/6

Figure 4: ADC gain calibrated

Awaiba Dragster V3-8K-3.5 Calibration Manual

Awaiba Dragster V3-8K-3.5 Calibration Manual

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