Differential-input piezoresistively-sensed square-extensional mode resonator for parasitic feedthrough cancellation

We have previously shown that parasitic capacitive feedthrough can be reduced by 60 dB for a resonator excited in an asymmetric mode shape. On the other hand, piezoresistive sensing offers substantial enhancements in transduction over capacitive sensing which are typically associated with symmetric modes. This makes any form of differential transduction difficult to implement for a piezoresistively-sensed resonator. In this work, we apply a passive differential input to a piezoresistively-sensed bulk mode square-plate MEMS resonator for suppressing parasitic capacitive feedthrough. We here show that an 11 dB decrease in feedthrough level is achieved using this new transduction configuration. We also show that the concept can be extended to other modes, in this case a length-extensional mode resonator where a feedthrough reduction of 21 dB was achieved.