Shafeeu, Hassan; (1995) Implementation of ultra-narrow-band switched capacitor filters. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

This thesis is concerned with the monolithic implementation of Switched Capacitor circuits for applications requiring bandpass filters with selectivities greater than 100 and at frequencies below 5MHz. Filters with these requirements have wide applications in telecommunications systems and in instrumentation, and are currently implemented using either electro-mechanical components or digital signal processing techniques. Fully integrated systems have potential advantages in terms of size and cost over these solutions. However, to realise these potential advantages, new circuit design and implementation techniques are needed for complex, single-chip filtering systems. SC design techniques available from the literature are used as the starting point for this project. High level building blocks that are required for high-Q filters are identified, and designed and implemented using MIETEC 2.4μm CMOS technology. Throughout the design, novel circuits were developed and verified with measured results. In total, over 60 mm2 of silicon area was used, which was spread over 5 ICs. The experimental results high-lighted the sensitivity of clock feedthrough in the architectures used. The results are used to propose a new circuit that will substantially reduce clock-feedthrough and the circuit is partially verified using the implemented ICs. The experience gained from the project was also used to develop a design methodology that can be used, for example, to implement high-Q filters using a high level specification, such as a mask definition. Finally, an important by-product of the investigation is a novel technique that can be used for wide ranging and continuous tuning of any circuit parameter that is determined by a capacitor ratio. This is useful for high-Q filters, since it will enable continuous on-line control of centre frequency and Q, thus allowing them to be used in adaptive filter applications.

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