A Micromechanical RF Channelizer

Clark Nguyen

Defense Advanced Research Projects Agency

This project aims to demonstrate an RF channelizer utilizing micromechanical elements in its signal path, and in the long term, a fully micromechanical radio. RF pre-select filters in use today (SAW’s, FBAR’s) employ resonator tanks with Q’s not much higher than 1,000 on average. This constrains their bandwidths to rather large values, making them only capable of rejecting out-of-band interferers and incapable of rejecting in-band interferers at adjacent channels. This then forces the rest of the receiver to handle the unattenuated in-band interferers, which raises the needed dynamic range of the processing circuitry, in turn raising the needed power consumption. If filters using resonators with Q’s > 10,000 were available, channel selection right at RF frequencies might become possible, which would then greatly relax the linearity, NF and phase noise specs for the LNA and subsequent demodulation electronics, in turn reducing the complexity, power consumption, and cost, of RF transceivers. The exceptional Q’s >10,000 of capacitively transduced ╬╝mechanical resonators makes possible filters capable of selecting channels right at RF. This in turn makes possible an RF channel-select filter bank capable of eliminating not only out-of-band interferers, but also out-of-channel interferers. Also, by using ╬╝mechanical mixer-filter devices, plus resonators as local oscillators, RF front-ends with transistorless signal paths are even conceivable. In this way, the high quality factor, stability, small size, and low cost of these devices enables a paradigm shift in transceiver design.