A MEMS BPSK demodulator : micromechanical mixing and filtering using MetalMUMPs

Abstract

In this paper two MEMS structures that are intended to demodulate a BPSK low data rate signal are compared. They are designed in conformity with the MetalMUMPs process. Target applications for such devices would be low-rate, wireless personal area networks (LR-WPANs) such as those described in the IEEE 802.15.4 standard onto which the ZigBee standard is built. The presented MEMS structures mix the Radio Frequency (RF) and Local Oscillator (LO) signals electrostatically and also filter this mixed signal prior to electrostatic sensing. These MEMS structures can also be used as the building blocks to demodulate higher order PSK schemes. The first structures' mode of vibration is torsional in nature and the use of torsional vibrations for BPSK demodulation is innovative. The first structure has an undamped resonant frequency of 2 MHz. The second structure is an extension of the first and is also supported on tethers exhibiting torsional vibrations. This structure resonates at 680 kHz.