MEMS-CMOS Heterogenous Mixed Signal Circuit Design
Sankhala, Devangsingh G.
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Various mixed-signal circuits form an integral part of modern electronic systems, whether portable or bench-top in size. Power converters, data converters and communication circuits are the three major categories of mixed-signal circuit paradigm. Switching power converters have been an area of interest for power conversion with a large conversion ratio. These have been demonstrated to exhibit a high power efficiency and smaller size. The switches in such power converters are implemented using Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET), however they are prone to various parasitic losses and leakages which in turn reduce the overall energy and area efficiency of the converter. Switch capacitor circuits have been in academic research since the late 1970s and have become a very important part of the data converter topology since the early 1990s. Accuracy and speed inevitably decides the figure of merit of such circuits. Thus, parasitic losses and leakages mar performance of these circuits. In the recent years, Micro-ElectroMechanical (MEM) and Nano-ElectroMechanical (NEM) relays have been manufactured reliably and demonstrated to work in applications like combinational and sequential logic, memory and power management circuits. The primary interest behind using such relays is the zero leakage current and constant on resistance. There have also been explorations in the NEMS-CMOS heterogeneous integration and back-end-of-line (BEOL) NEMS integration on CMOS. This dissertation explores aspects of hardware implementation of MEMS switches in various mixed signal circuits. Owing to a constant on resistance over a slewing gate voltage and infinite off resistance, it offers a new design perspective for low power mixed-signal designs. A charge pump is demonstrated to explore implementation constraints and efficiency of the switch when used in a power converter. For a data converter implementation, a switch capacitor voltage amplifier and a sample and hold amplifier is demonstrated to analyze the accuracy of the proposed implementation. MEMS switches show exceptional results in terms of area, power efficiency and accuracy when implemented in the aforesaid designs. However, certain restraints are shown based on commercially available switches and an attempt is made to overcome them.