A Fully-Differential CMOS-MEMS Resonator Integrated with an On-Chip Amplifier

A fully-differential CMOS-MEMS ring resonator integrated with a differential-type transimpedance amplifier (TIA) has been demonstrated using a commercially available CMOS process with 30-dB feedthrough suppression as compared to its singled-ended counterparts. To achieve such performance, the flexural-mode ring resonator with a desired mode shape features an inherent differential mode of mechanical operation, therefore not only enabling feedthrough (i.e., common-mode) signal cancellation to attain a clean frequency characteristic of the motional signal but attaining high Q due to its symmetrical structure and nodal support design. The nodal locations of the ring can be precisely accessed by the supporting beams due to its geometrical symmetry by which the process variation would not affect the motionless positions of the ring, therefore assuring low vibration energy loss and high Q. In addition, the on-chip differential TIA provides both the signal gain and impedance matching to further enhance the transmission of the motional current for future single-chip oscillator implementations. As a result, such a CMOS-MEMS ring resonator together with its on-chip circuitry offers a potential benefit from capacitive feedthrough cancelation by means of differential signaling scheme. Theoretical predications and simulations are in good agreement with the experimental demonstration.