Capacitive micro-machined sensor force-feedback mode interface system

Description

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 stabilising 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.

Aspects

The problem of stabilizing Σ-Δ electro-mechanical loops in the presence of high-Q parasitic modes is addressed. In one embodiment, introducing a second order finite impulse response (FIR) filter into the Σ-Δ electro-mechanical loop stabilizes the loop. This solution is supported by both theoretical and empirical results and is much simpler than other proposed techniques.

Patenting Status

Pending

Status

Idea/Concept

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