Date

2018

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Electrical Engineering

First Adviser

Frey, Douglas R.

Abstract

The design of high-performance low-noise bandpass filtering systems has been studied from several aspects: (1) applying the synchronous filtering idea to the development of externally linear, time-invariant filters which can be internally nonlinear and/or time-varying, (2) seeking solutions to improve the noise performance of these filters, from parameter configuration to architecture design, and (3) implementing the systems of interest as transistor level circuits and verifying their function.Particularly, the state space representations for a biquad AM mode synchronous bandpass filter and a biquad FM mode synchronous complex filter have been proposed and realized with ideal Gm-C networks and log-domain circuits. Both systems utilize the modulator-core filter-modulator architecture to synchronize the internal signal processing. The core filter in an AM mode synchronous filter has constant center frequency and time-variant bandwidth, and the terminal modulators perform amplitude modulation to maintain the system’s external linearity and input/output characteristics. An FM mode synchronous filter typically has time-invariant bandwidth and performs frequency modulation before and after the signal filtering. Depending on whether the center frequency and terminal modulating frequency vary with time, there are static and dynamic types of FM mode synchronous filters. They both have the advantage of being able to filter the high frequency input signals in a low frequency range, which greatly alleviates the design and integration challenge due to the high frequency limitation of active components. Moreover, some dynamic filters effectively suppress the injected single-tone noise and generate an output with much higher SNR in comparison to the output from a static filter that implements the same transfer function.As a variation of an AM mode synchronous bandpass filter, the system derived by removing its back end modulator has been verified to have impressive noise reduction capability when processing noisy AM signals. Furthermore, it inspired the development of a feedback filtering system, the effective bandwidth of which could be tuned by scaling the feedback signal that time varies the core filter’s instantaneous bandwidth. It further provides an innovative approach to the design of a high-Q filter with superior immunity to internal noise, using a filter with very low Q factor. Finally, a design that combines the feedback architecture and the biquad FM mode synchronous complex filter is proposed and implemented as a log-domain filtering circuit. Appealing features of this system include wide dynamic range, flexible bandwidth and center frequency tunability. Since there is a low requirement for the high-frequency performance of active components, these filters make a good fit for monolithic integration, and greatly improved immunity to in-filter noise in comparison to that of an open loop complex filter with similar external filtering capability.

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