Application of analogue charge-coupled devices to adaptive signal processing

• Main Author: Cowan, Colin Frederick Nathaniel
• Published: University of Edinburgh 1980
• Subjects: 621.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645053

In this thesis the application of analogue charge-coupled devices (CCD's) to adaptive signal processing is considered. This research has lead to the design of several novel signal processing modules which have been evaluated here with reference to the inherent error sources in analogue CCD circuits. Error sources such as charge-transfer inefficiency and dark current integration have been evaluated in the context of specific circuit architectures and appropriate techniques for the minimisation of these effects have been advocated. The problem of drift in analogue circuits has also been examined and a particular system implementation which appears to be largely immune from this problem is described. The processors described in this thesis are all baseband systems working at clocking rates between a few hundred Hertz and about 500 kHz. The areas of application being investigated therefore include voiceband processing, high speed modems and sonar applications, including some applications in medical electronics which also fall within the operational range of these processors. Basically, two classes of CCD signal processing module are considered; open-loop and closed-loop modules. These two classes of filter may be broadly defined as processors which have fixed impulse response characteristics (open-loop) and those which employ feedback to adjust their own filter weights according to an estimate of the accuracy of the filter output (closed-loop or true adaptive processors). Two open-loop experimental modules are described: (1) a statistical analyser module which is capable of detecting pulses in noise by the use of an adaptive thresholding technique which automatically measures noise level at the system input: and (2) a module which adaptively cancels the fixed pattern noise on the output of a serial-parallel-serial CCU delay line by the use of a coherent integration technique. Both these modules illustrate the advantage of analogue CCD circuits over standard digital techniques in terms i of power consumption and speed of operation. However, they also illustrate a major problem with analogue CCU circuits which is that of d.c. stability. Under the heading of closed-loop processors two experimental CCU adaptive filters are described. One of which is based on a monolithic 64-point programmable filter (PTF) and the other based on a monolithic 256-point PTF. The main features demonstrated using these modules is the inherent correction of the errors described above when the CCD filter is in a closed-loop configuration and also the inherent d.c. stability of these systems in this configuration. Results are presented which demonstrate the predictability of these modules from theoretically ideal models and also their operation in such key applications as adaptive cancellation and line equalisation.