Design of Fully Digital Inductors for Low Bandwidth Filter Applications

Abstract

We are currently living in the age of intelligent machines, where we are interested in acquiring data and making decisions all from some sort of embedded environment. Of particular value are personal health metrics, such as the analysis of heart rate, muscle action potentials, and brain waves. Collecting this data requires new advances in the circuitry behind much of classical filter design. In this thesis, we present a digital inductor based on time-domain signal processing. This approach uses the phase-domain theory that is well-known and understood in the fields of clocking and serial links and applies it to analog circuit design. By using a ring oscillator to integrate the input voltage and a switched transconductor to inject current into the input node, the proposed time-domain gyrator achieves inductive input impedance without using either large resistors or capacitors. Realizing the gyrator in this manner makes it significantly more amenable for technology scaling. Fabricated in 65 nm CMOS process, the inductor operates from a 0.7 V supply voltage and consumes 528 µW. Measurement results show inductance values in the range of 150 µH to 1.5 mH can be achieved.

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Master’s Thesis
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