Calibrating CMOS Detectors for Scientific Measurement

Solar physicists study the hot plasma, waves, magnetic fields, and energy release of solar flares
by imaging them in x-ray and extracting data from those images. The digital image sensors that
are used today—called CCD (charged coupled device)—have major limitations in imaging solar
flares. Solar flares’ soft x-ray and EUV emission varies in intensity along magnetic loops and
varies over short time frames. Current CCD imager pixels readout is sequential through a single
amplifier (gain) resulting in relatively slow readout speeds. Thus during solar flares, CCD suffer
from saturation and blooming. Because of this, CCD images of solar flares often contain very
little usable data. To avoid this we can use CMOS (complementary metal oxide semiconductor)
detectors, which have signal amplification on each pixel and parallel column readout, resulting
in 10-100s times faster performance than CCD. Hence CMOS will mitigate saturation and
blooming.
The ultimate goal of this project is to develop processing software to determine the gain per
individual pixel for any CMOS device given a CMOS measurement and a known source flux.
The first step to achieve this goal during the summer of 2020 I simulated a CCD detector signal
with a predefined illumination of monoenergetic photons.This included a fixed signal offset
(signal bias), random noise (gaussian distribution), and fixed gain across all pixels. I created a
histogram with the charge values of each pixel and fit two gaussian curves to the histogram data
(one to the bias curve and one to the signal curve). The gain can be determined by fitting the
gaussian amplitude, centroid, and standard deviation. Further improvements to the code will
help future researchers characterize CMOS detectors, operate them on space observatories,
and better capture dynamic phenomena in solar flares.