- 學位論文
低雜訊讀取電路應用於電容式壓力感測器之研究
A Study of Low Noise Readout Circuit on Capacitive Pressuree Sensor Device
摘要
本論文提出一種利用MEMS壓力計結合COMS電路，將感測訊號直接與讀取電路相接，此訊號處理單元為電容量測單元，因此能夠直接量測及為極微小電容訊號變化。主要目的為偵測高度的壓力。後階段可利用MEMS壓力計陣列形式，以提高不同的壓力感測範圍，以發揮電容感測器的辨識能力，實現可穿戴式（Wearable）或植入式(Implantable)單晶片（SoC）之目的。 由於MEMS壓力感測器在感測壓力時，電容訊號變化約為1fF~100fF等級經由公式推算出微結構的初始電容值和電容變化值，利用讀取電路做偵測。在感測讀取電路方面，採用開關電容(Switched-Capacitor,SC)電路架構，並採用雙相關取樣技術(Correlated Double Sampling,CDS)來減少電路本身的偏移(offset)以及降低放大器本身的雜訊 。為了增加輸出動態量測範圍，在電路增加一可編程增益放大器。本文的晶片是經由TSMC 0.18μm 1P6M CMOS製作，電壓1.8V，在正常運作模式下，功率消耗約為0.7mW。本文完成了一個低雜訊的電容式感測器讀取系統，其電路模擬上解析度可達12bits，約可達到1fF電容變化量的感測靈敏度。
並列摘要
In this thesis, a new type of MEMS capacitor sensor composed of pressure and CMOS circuitry is proposed. The tiny capacitor variation can be measured directly by means of the proposed sensing circuit, which is composed of an read-out circuit. The goal of the designed sensor is used to detect the pressure of altitude. Furthermore, an array-typed MEMS pressure sensor can be detect altitude in various pressure ranges, and it is desired to become a wearable or an implantable device. The sensing capacitor range of the proposed sensor is about several fF ~ hundreds of fF, by using readout circuits and comparing the I/O wavforms, and we can calculate the capacitor initial value and variation of MEMS pressure sensor. As to measurement of capacitor, we chose switched-capacitor (SC) interface circuits and Correlated double sampling(CDS) technique is used in SC circuits to minimize offset and noise of the amplifier. In order to improve the dynamic range of output, we use programmable gain amplifier to add third stage in read-out circuit. The chip was fabricated in TSMC 0.18um 1P6M CMOS process, dissipates 0.7mW at 1.8V in a typical sensors application utilizing periodic operation mode. It achieves low noise performance while the resolution of capacitive mode sensors is about 12 bits. This paper presents a circuit of weak capacitive variation measurement .