High Dynamic Range Imaging with sCMOS (Scientific CMOS)

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Fairchild Imaging, PCO and Andor Technology adapt CMOS technology specially for the needs of scientific imaging.

Scientists are reporting that the new sCMOS technology is proving essential for scientific imaging applications because, for the first time, it is allowing for the accurate measurement of structures that are very dim as well as structures that are very bright in the same field of view. Scientific imaging applications such as fluorescence microscopy will realize significant benefit from this high dynamic range delivered by sCMOS technology. In addition to intra-scene variation, inter-scene variations in intensity also require a camera with a large dynamic range. An example of this is calcium ratiometric imaging where signals can vary greatly in intensity on a frame to frame basis.

The dynamic range of an image sensor is defined as the ratio of the maximum to minimum signal that can be measured. In practice, this is determined by the ratio of pixel full well capacity to the readout noise. Therefore, large pixel full well and small readout noise are both necessary for optimal dynamic range. In order to utilize the full well of a CMOS pixel, the amplifier gain must be kept low. For example, given a 1.5V swing on the output of the amplifier, a 30,000 electron signal will require a gain of 1.5V/30,000e- = 50uV/e-. This will allow measurement of the full well signal but will not allow for the lowest possible read noise. In order to get a very low readout noise and the resulting superior sensitivity, a value of 1500uV/e- would be ideal but this would mean that the largest signal would be limited to 1000e- maximum which is only 1/30th of the total well size. This leaves a quandary of whether to choose maximal sensitivity or high dynamic range imaging.

PCO, Andor and Fairchild together have taken a novel design approach in sCMOS technology by implementing both approaches simultaneously. sCMOS technology has a high-gain amplifier to get the lowest possible noise on one output and a low-gain amplifier to get the largest possible signal on another output. These two amplifiers are simultaneously read out and converted into digital values allowing both signals to be combined for a higher dynamic range image.

As shown in the sCMOS White Paper released on June 16th at the Laser World of Photonics show, both circuits incorporate high performance 11 bit ADCs to produce 2048 gray levels of significant data. Both outputs are sent to the camera which could either combine the data into one 16 bit image or leave it in two 11-bit data streams. This means, depending on the camera system, that a user could select high sensitivity data for one application, high signal data for another application or a combined high dynamic range data that maintains high SNR for both the low and the high end of the data range.

This approach allows the scientific user to get high quality linear data for both dim and bright targets within the field of view while getting unparalleled sensitivity due to the ultra-low noise of the readout. This high dynamic range combination makes sCMOS technology a compelling solution for many scientific imaging applications.


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