An improved correlated double sampling circuit for low noise charge coupled devices

Correlated double sampling (CDS) is discussed as a signal processing method to reduce low-frequency amplifier noise and kTC noise of sampled systems. The different noise contributions in a typical CCD output stage and their transformation through a CDS circuit are discussed. An improved CDS method (CDS2) is presented that completely eliminates the pixel crosstalk and kTC-noise contribution, but maintains a low noise bandwidth. The noise reduction achieved with the method lies in the range of 3-8 dB, with the lower limit valid for white noise and the upper limit for pixel crosstalk and kTC noise. The improved CDS circuit approaches optimum filtering of the combined noise spectrum. From the hardware point of view only one additional switch is required. Measured values with an experimental CCD output stage and CDS setup are shown to confirm the theory