# Sustaining amp circuit for MEMS oscillator

A MEMS oscillator can be modelled as a lumped mass-spring-damper with a high resonant frequency and Q factor.

According to Wikipedia "All commercial MEMS oscillators use electrostatic transduction". i.e the resonator motion is detected with a capacitor. An Electronic sustaining amplifier detects the resonator motion and drives additional energy into the resonators driving the resonator in continuous oscillation.

What is a simple circuit that will achieve this? I need a circuit that will drive the oscillator at its resonant frequency. I need the simplest circuit possible, just for mathematical modelling purposes, so I'm not interested in advanced features or practical considerations.

• I'm pretty sure you can use the same kind of circuit as you would use for a crystal oscillator. Since you'll be modelling/simulating, you can check whether this is true. See this question for some ideas: electronics.stackexchange.com/questions/36256/… Commented Apr 3, 2015 at 13:54

Try this although I'm a bit out of my depth: -

The mems resonator above looks like a double cantilever to me and it appears that input to and output from are via capacitive coupling (see drive electrode and sense electrode). The dimension of 50um is on one of the cantilevers and, I imagine that it's movement creates a twisting effect on the sense electrode thus altering capacitance and generating a sense signal when polarized with DC.

Here is a useful document (entitled CMOS Micromechanical Resonator Oscillator) that importantly has this diagram that kind of puts into perspective what I said above: -

It also contains the picture below that gives a detailed interface circuit: -

What is a simple circuit that will achieve this? I need a circuit that will drive the oscillator at its resonant frequency. I need the simplest circuit possible, just for mathematical modelling purposes, so I'm not interested in advanced features or practical considerations.

Ah, if only everything in life were simple but maybe the circuit in this document (entitled Drive Amplitude Dependence of Micromechanical Resonator Series Motional Resistance) will help: -

There are a few other documents listed here

• Thanks, this is useful, especially the first link. It's also a lot more complex than I thought it would be. Can I just ask, do you think its likely that the frequency of the sustaining amplifier output (The TIA) will be equal to the resonant frequency of mechanical micro resonator at steady state? This is what I'm trying to prove with a mathematical model, but the model for the TIA will be too complex, so I think a guess will have to do. Commented Apr 3, 2015 at 15:12
• The sustaining amplifier will produce a frequency output that mimics the input or it ain't doing a good job! Commented Apr 3, 2015 at 15:41