Method for extending the dynamic range of CCD instruments

Charge coupled devices (CCDs) are the detector of choice for instruments that detect low levels of light for wavelengths 300 nm <EQ (lambda) <EQ 1100 nm. Contemporary devices have read noise level equivalents of a few electrons, and the ability to store over 100,000 electrons per pixel. In order to take full advantage of these characteristics, while ensuring that digital quantization noise will not dominate over readout noise, the dynamic range of the readout system must exceed 18 bits. We present a simple scheme that exploits the fact that Poisson noise dominates the error budget in most contemporary CCD systems in order to achieve an effective dynamic range of over 20 bits by suing dual 16 bit A/D converters of different sensitivity.