Improving and characterising the threshold equalisation process for multi-chip Medipix3 cameras in Single Pixel Mode

The Medipix3 (MP3) detector is the most recent addition to the family of Medipix spectral x-ray detectors. It offers many advantages to the previous version of the Medipix detector, such as charge summing mode, dual counters, improved radiation hardening and the ability to operate in continuous read/write mode. Although these added features provide beneficial advantages, there are still some drawbacks. The variation in the pixel to pixel applied thresholding across the MP3 chip is much larger than in the second generation of the Medipix chips. To help with this, each pixel has 5 bits to adjust the threshold. There are also two global current sources that are applied to these adjustment bits, allowing for a fine grain of threshold control. With this, the spectral performance of the MP3 detector is comparable to the second generation of detectors. To use MP3 chips effectively, a well designed chip equalisation process is required. The original equalisation process employed by the MARS research group relies on a predetermined threshold distribution based on single chip detectors. This allows for a reasonable threshold response to be acquired quickly, but has room for improvement by adjusting more parameters. To improve the equalisation process, the MP3 detectors need to be characterised. Specifically, measurements are required relating threshold response to threshold adjustment parameters. Results of these measurements are shown and used to implement an improved threshold equalisation process for multi-chip MP3 detectors.