A New Discrete Analog Circuit Solution for Capacitive Rotary Encoders

Abstract

In the time of global chip crisis, it is clear that alternative electronic solutions are necessary; particularly for capacitive rotary encoders, or similar capacitive sensors where demodulation techniques are extensively used. In this work, a discrete analog switch based circuit solution is proposed for the capacitive rotary encoders for the first time in the literature to the best of our knowledge. A 3-layer uniquely designed capacitive encoder prototype is used as a capacitive sensor. The analog switch with OPAMP based demodulation configuration designed for this work is both cheaper and it works at higher frequencies than the analog multiplier configuration. Also, unlike ASIC, it does not require high-tech for production. With the established test setup; noise, smallest perceptible capacitance, nonlinearity and temperature analyses of the circuit were made and competing results were achieved. The noise levels in terms of degree and voltage are measured as 0.0063° and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$36.62~\mu \text{V}\sqrt {\text {Hz}}$ </tex-math></inline-formula> ; respectively. Minimum measurable capacitance achieved with the discrete analog circuit is 2.54 aF <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\text {Hz}}$ </tex-math></inline-formula> . Nonlinearity was found to be 0.29% which is highly correlated with the mechanical misalignments of the capacitive encoder. Although this particular study is carried out on capacitive encoders, the proposed circuit solution can be used for similar types of sensors.