Characterization and control of a high-Q MEMS inertial sensor using low-cost hardware

We propose a high-performance, low-cost system for control and characterization of MEMS rate and rate-integrating gyroscopes and other resonant sensors. MEMS gyroscopes, some accelerometers and clocks utilize mechanical resonators. High-quality factor, low-frequency resonator devices with damping time constants from seconds to several minutes pose special characterization challenges. The proposed system uses the commercial “USRP” software defined radio (SDR) hardware and open source GnuRadio software as a platform for the proposed characterization and control system. For characterization of resonators, we developed software to perform dual channel swept-frequency gain-phase analysis, impulse response real-time spectral analysis, and ring down testing which achieve performance comparable to dedicated commercial hardware. To highlight the capabilities of the characterization tools, we implemented an automatic mode matching algorithm in the software. The same hardware is used for control of gyroscopes in either rate or rate integrating modes. We present here two control schemes; a rate-only control implemented entirely in the FPGA of a USRP1, and a hybrid software/firmware control which is capable of rate and rate-integrating operation. Experimental results of characterization, automatic tuning and rate-mode operation of a rate and rate-integrating MEMS gyroscope are presented to demonstrate the viability of the proposed system.

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