A new low-noise CCD signal acquisition method based on a commutable band-pass filter

A new Correlated Double Sampling (CDS) method for low-noise CCD signal acquisition is presented. The method is based on the utilization of an active band-pass filter with adjustable frequency characteristics. By varying the filter parameters in sequence with the pixel readout, the signal information may be extracted while keeping the equivalent noise bandwidth low. This new acquisition method is simple to implement, offers low-noise performance (close to double integrators), and has several other advantages compared to the other acquisition systems in use. We also present the derivation of a mathematical model to simulate the signal-to-noise ratio for a given CCD output noise characteristic and pixel readout frequency. Our model considers the nonstationary nature of the signal at the sampling instant which implies that the usual way of calculating average noise power (using the filter's transfer function) is not valid. Theoretical results are compared with experimental data and the noise performance of this approach is compared with other CDS methods now in use.