Digital Signal Tuning System for MEMS Excitation

P. Wiegand, A.A. Ahmad, B. Spetzler, R. Rieger (Kiel Univ., Germany)

This paper presents an ASIC system for the precise tuning of an excitation signal frequency with a very high resolution on the order of 4 ppm. It is used to drive a resonant micromechanical sensor at its exact resonance frequency. The system receives a low-jitter reference clock at its input and produces a signal with a lower fundamental frequency at its output, programmed by a 9-bit digital control word. Measured results from an ASIC implemented in 350 nm CMOS technology are shown. Also, a setup is demonstrated in which the signal is precisely tuned to the resonance frequency of a custom-made resonant micromechanical magnetic field sensor. Magnetic field measurements are carried out that show that the miniaturized ASIC system achieves performance comparable to a bench-top laboratory frequency generator regarding noise, sensitivity and limit of detection in this application.