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Scientific CMOS (SCMOS) image sensor

The latest development in imaging technology, scientific CMOS (SCMOS) sensors simultaneously deliver high sensitivity, fast readout speeds, and low noise without the addition of multiplicative noise associated with EM-CCDs. The combination of high sensitivity and low noise ensures high signal-to-noise ratio during low-light imaging.These image sensors have pixels composed of a photodiode and an amplifier that converts charge into voltage. The voltage of each pixel is output by turning on the switch one by one, and the data of each horizontal line is read by the on-chip column amplifier and A/D in parallel and simultaneously. This results in very fast readout speed while keeping the readout noise very low. Hamamatsu SCMOS cameras are designed to offer unprecedented sensitivity (because of high QE and low noise) with minimal pixel gain variation and fast frame rate.

Popular cameras are listed below.

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Effects of Camera Specifications on Relative SNR. Historically, Nr has been the primary camera spec used to define sensitivity. With the performance of Gen II sCMOS, it is crucial to understand how QE, Nr and Fn all affect SNR. The purple line is the relative SNR for a perfect camera. The numbers above this line indicates the SNR ratio at a series of intensities and SNR = 1 is indicated by a star on each curve. Because this is a perfect camera, these SNRs are only limited by photon shot noise. For each of the three real cameras on this graph, there are bars below that represent regions of each curve. At lowest light level, shown in region (A), Nr dominates relative SNR calculations (S < Nr2/(QE * Fn2) and the crossover into shot noise dominated regions is the upper boundary of this low light region (triangle, 2.3 photons for ORCA-Flash4.0 and 50 photons for CCD). The (B) region is the intermediate zone, where Nr, eQE and Fn all contribute to the relative SNR. We define the upper boundary of this region as the point at which the curve is 95% of the maximum relative SNR for that camera (arrow, 20 photons for ORCA-Flash4.0 versus 550 photons for CCD). The (C) region is the high light region where eQE is the only camera parameter that matters (SNR loss shown by vertical brackets). These three regions are easily defined for the ORCA-Flash4.0 and for an interline CCD, both of which have Fn = 1. For EM-CCD the curve is flat. Except at the very lowest light levels, the EMCCD curve mirrors the shape of the perfect camera almost exactly, except that SNR reduced to 0.68 of the value of the perfect camera. Thus, it is clear that in spite of low Nr and high apparent QE, the SNR of the EM-CCD is greatly affected by Fn = 1.4, and all input light levels in the EM-CCD reside in the region where eQE dominates.

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Comparison of image uniformity between the Gen II ORCA-Flash4.0 and a Gen I sCMOS camera. (A) sCMOS requires careful sensor and camera design to ensure uniform response for every pixel in the image. The ORCA-Flash4.0 has excellent image uniformity. (B) Gen I sCMOS shows vertical stripes. Because such patterns may not appear at low light levels it is important to look for these stripes at other intensities.

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