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Low-power, small-form factor angle sensing circuit for an electrostatic, quasi-static MEMS mirror in AR applications

Bergen Albert Fletcher
Daniel Malea
Matt Wakelin
Sangtak Park
SPIE AR VR MR 2022 (2022)

Abstract

This paper presents a new, low-voltage, small-form factor analog front-end (AFE) circuit that measures the torsional angle of an electrostatically-actuated, quasi-static MEMS mirror, while it operates at a frame rate of 50 Hz to 60 Hz, following a given reference profile, such as a sawtooth or triangle profile. The quasi-static MEMS mirror is actuated with two high voltage (HV) differential signals. To enforce this quasi-static MEMS mirror to track a given angle profile or trajectory with minimum error, the MEMS mirror is driven by feedback control that requires a sensor capable of measuring its mechanical or optical angle in real time with high enough bandwidth and sensitivity. Hence, we design and implement the angle sensing circuit (ASC) that meets the low-power, low-cost, and small form-factor requirements to reduce power consumption, size, and weight for AR applications. This ASC consists of a variable gain amplifier (VGA) and an envelope detector that operates at 3.3 V and draws about 1 mA during operation.

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