單晶片微機電諧振器整合之振盪器設計及其延伸應用於多元感測

Abstract

本論文提出可於標準1P6M 0.18μm電路製程下，完成可單晶片整合之電容式高品質因素微機電震盪器以及轉阻讀出電路設計。震盪器設計上採用梳狀式結構並以靜電力致動產生共振現象。在氣壓20帕下之真空腔內可測得品質因素高達2600，共振頻率設計在32.768 kHz以應用於時脈產生器。 震盪器之電容變化轉換可得到輸出電流變化，利用轉阻放大電路讀取電流並輸出電壓訊號回授至震盪器產生共振。轉阻放大電路採用電容式回授架構並利用電容源極退化(Capacitive Source Degeneration)技巧拓展頻寬與補償相位移，其增益高達107MΩ以克服微機電震盪器之高介入損耗，頻寬為235.8kHz使得在32.768kHz時僅有1.3度的相位移，核心電路功耗僅1.836μW達成低功率之微機電時脈產生器。 為了從整合的前端電路取得精準值，採用感測器電腦輔助設計軟體與電子設計自動化軟體模擬整合後的微機電震盪器暨低功耗轉阻放大電路，藉以具體分析模擬與實際量測之差異，並完成微機電製程與積體電路整合設計流程。

A monolithic low-power MEMS oscillator is proposed for 32-kHz real-time clock based on the 0.18 μm 1-poly-6-metal standard CMOS-MEMS process and monolithically integrated with TIA readout circuitry. The system consists of an electrostatic-actuated resonator along with the TIA readout circuitry inside the oscillator loop. The MEMS resonator is measured for high Q value of 2600 at 40 pa pressure with moderate motional impedance under strict design constraints of the fabrication process. A high gain low-power capacitive-feedback TIA readout circuitry is designed to overcome the high insertion loss from the input to the output of the MEMS resonator. The proposed TIA takes advantage of the capacitive source degeneration technique as well as Shunt-Series feedback topology converting output current to voltage through a load resistance to achieve 107 MDC gain and 1.3° phase shift respectively at target frequency and the bandwidth is 235.8 kHz with power consumption of 1.836 μW. It can be compactly integrated with the MEMS resonator structure on a single die for low-power 32 kHz clock generation. The proposed MEMS oscillator can be embedded monolithically as a real-time clock source in common SoC applications with the standard CMOS process.