Electronic compensation of capacitive micro-machined sensors parasitic modes in force-feedback interface systems

摘要

Operating capacitive sensors in force feedback mode has many benefits, such as improved bandwidth, and lower sensitivity to process and temperature variation. To overcome, the non-linearity of the voltage-to-force relation in capacitive feedback, a two-level feedback signal is often used. Therefore, a single-bit Σ-Δ modulator represents a practical way to implement capacitive sensors interface circuits. However, high-Q parasitic modes that exist in high-Q sensors (operating in vacuum) cause a stability problem for the Σ-Δ loop, and hence, limit the applicability of Σ-Δ technique to such sensors. A solution is provided that allows stabilizing the Σ-Δ loop, in the presence of high-Q parasitic modes. The solution is applicable to low or high order Σ-Δ based interfaces for capacitive sensors.

主权项

1. A method of electronically interfacing with a MEMS sensor using an interface circuit, the MEMS sensor and the interface circuit together forming a sigma-delta modulator loop, the method comprising:
identifying a potential parasitic resonant mode of the sigma-delta modulator loop, the potential parasitic resonant mode having a frequency and a quality factor; inserting into the sigma-delta modulator loop a filter having characteristics chosen in accordance with at least one of the frequency and the quality factor of the potential parasitic resonant mode.