The Research On The Design And Application Of Log-domain Companding Filters (Circuits)

Log-domain companding technique takes advantage of the exponential I/V characteristics of the active devices such as bipolar junction transistors (BJT), compressing the dynamic range of the input sigal and reducing internal voltage amplitudes, it can maintain large dynamic range and high operating frequency under low supply voltage , the main area of application for this technique is the implementation of continuous-time fully integrated filters (or circuits) with low voltage, wide dynamic range, high-frequency, and wide tenability.First of all, the thesis introduces the the exponential I/V characteristics of the active devices and the principles of both static and dynamic translinear circuits, and based on the basic topology of log-domain integrators, presents the circuits of non-inverting signal-input log-domain integrator, inverting signal-input log-domain integrator, differential dual-input log-domain integrator and class-AB log-domain integrator, investigates and compares the power efficiency of log-domain integrator and the linear Gm-C integrator, it is shown that log-domain filters are better suited for low-power signal processing at low supply voltages, then effects of transistor nonidealities on log-domain filters are investigated and the compensation schemes are also proposed.Secondly, several sythesis methods of log-domain filters are introduced, the first method is a modular approach, it is based on the operational simulation of the LC ladder networks, the method is used to design a third-order Chebyshev low-pass log-domain filter, a fifth-order Chebyshev low-pass log-domain filter and a second-order band-pass filter, and the behavior of these filters is verified through the PSPICE simulation; the second method is a systematic transistor-level analysis andsythesis method of log-domain filters--the Bernoulli Cell approach, a lossylog-domain integrator and a second-order low-pass log-domain filter are designed based on the method and the results of the simulation are also presented; the third method is state space synthesis of log-domain.filters, based on the novel all-NPN positive and negative exponential transconductance cell, an improved second-order log-domain oscillator is designed using the state-space sythesis method, then a third-order universal log-domain filter is designed also using the state-space sythesis method.Lastly, the thesis investigate the application of log-domain filter in the hard-disk-drive (HDD) read channels, audio-frequency filtering, the design of current-mode phase-locked loop ( PLL) and the VLSI implementation of wavlet transformation etc, then introduces the square-root domain filters using quadratic law of MOSFET in strong inversion region which also belong to the class of companding filters, a square-root domain integrator is also presented.