At low light illumination, the frames in video stream might need to be combined to get a sufficient SNR for identification purposes. In most sensors, the frame addition also adds the read noise, so the SNR grows as square root of the number of frames. Due to the non-destructive read capability, Pixpolar's MIG pixel can be reset once per many video frames. Then the video frames are extracted by subtraction, while the integrated long frame between the resets carry just one-time read noise component.
Pixpolar's demo of the idea is marred by the fact it assumed the CIS sensor to have lower QE than its MIG pixel (not sure why), but it illustrates the approach:
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| Simulation result presenting the signal-to-noise ratio enhancement when multiple frames are merged together in high end CIS and MIG technologies. The simulation was done for low intensity NIR illumination (50 photons / second in brightest areas). QE in CIS was assumed to be 28 % and in MIG 70 %. The read noise in both sensors was assumed to be 1 e-. Dark current in CIS was 0 e-/s and in MIG 1 e-/s. The frame rate was 25 fps and in total 50 frames was merged together. |