B. Conversion Gain Measurement
In order to measure the conversion gain of the readout chain,
the photon transfer curve (PTC) measurement technique is
used [18]. Fig. 12(a) shows the variance versus the signal PTC
of the sensor measured from 5000 pixels. It is obtained using
the analog output of the sensor and the column-level gain set to
64. The sensor is exposed uniformly to different levels of light
provided by the LED and controlled with the voltage source.
Fig. 11. The designed PCB board and the assembled optical objective used
to test the presented image sensor.
Fig. 12. Variance versus signal photon transfer curve (PTC) of the image
sensor with (a) ×64 column-level gain and (b) ×1 column-level gain.
The variance and mean value are extracted from 100 images
for each light level. The PTC curve collapses around 2 V due
to the column-level readout chain saturation. The measured
conversion gain is 160μV/e−. It is measured by estimating
the slope factor in the linear part of the PTC and dividing it
by the measured gain of the readout chain. Fig. 12(b) shows