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

Abstract

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.

Non-stationary noise responses of some fully differential on-chip readout circuits suitable for CMOS image sensors

“…When the input noise is dominated by -noise, especially for low pixel readout rates (for example, less than 50 frames/s for a 256 256 pixels array), the commutable bandpass filter is very suitable. However, it can be pointed out that, while it shows good noise performance for CCD's [7], with the common CMOS active-pixel image sensor readout architecture [1, Fig. 1], it has no effect on the noise generated by the in-pixel source follower MOSFET, because this noise is already stored on the sampling capacitors and .…”

“…A different and nondifferential version of this circuit is proposed and studied in [7] for a Thomson 7895M scientificgrade CCD off-chip signal acquisition systems, with low pixel (25 kpixels/s typically) readout speeds.…”

“…The approach for the generating process used here is based on a Markovian input-output representation of fractional noises, elaborated from an infinite-dimension stochastic differential equation developed in [11], [12], and in a slightly different way in [7]. If (5) then is -noise.…”

“…The noise response may be calculated directly by using the stochastic differential equations [7]. But it requires the handling of large matrices and the simulation needs large time computations.…”

Analysis and reduction of signal readout circuitry temporal noise in CMOS image sensors for low-light levels

“…In other words, the signal and noise transients are ended and both signal and noise means are no more varying. Otherwise, the MOS transistor noise models used would not be usable and a nonstationary state variable method should be used [17]- [19].…”