Continuous MEMS Capacitance Measurement Using Lock-In Amplifier

The patent applies periodic action by using alternating current (AC) signals at specific frequencies to excite the capacitance measurement circuit. The AC signal is periodically applied across the capacitor under test, allowing continuous measurement without disconnecting power. The lock-in amplifier detects the capacitive reactance at the signal frequency, enabling ongoing capacitance tracking while the MEMS actuator remains powered and functional.

The patent introduces an intermediary measurement circuit that includes a voltage divider network and current measurement path. Instead of directly measuring capacitance disruption, the system uses an intermediary current signal that flows through the capacitor and measures the resulting current response. This intermediary approach allows capacitance to be inferred from current measurements while maintaining continuous power delivery to the MEMS actuator.

The patent uses periodic AC excitation at a specific frequency and employs a lock-in amplifier that is synchronized to this frequency. The lock-in amplifier filters out all noise and interference that does not occur at the reference frequency, effectively separating the signal of interest from background noise. This periodic action with synchronous detection enables high-precision measurements while maintaining continuous power connection.

The patent converts the harmful effect of noise and interference into a beneficial filtering mechanism. By using a lock-in amplifier tuned to the specific excitation frequency, the system exploits the fact that noise and interference typically occur at different frequencies. The lock-in amplifier's narrow bandwidth effectively filters out these unwanted signals, transforming the noisy environment into a controlled measurement condition that enhances precision.