Theoretical analysis and optimization of CDS signal processing method for CCD image sensors

The correlated double sampling (CDS) signal processing method used in processing of video signals from CCD image sensors is theoretically analyzed. The CDS signal processing is frequency used to remove noise, which is generated by the reset operation of the floating diffusion charge detection node, from the signal. The derived formulas for the noise power spectral density provide an invaluable insight into the choice of the circuit parameters affecting the noise spectrum. The obtained results are useful for determining the optimum cutoff frequency of the low-pass filter which precedes the sample-and-hold circuit and for finding the optimum size of the input transistor in the first amplifier stage. Once the optimum parameters are determined it is possible to find the minimum electron equivalent noise and the maximum signal-to-noise ratio achievable with this signal processing method. The validity of the derived theoretical results is confirmed by making comparisons with the experimental data