應用於冷鏈物流之環境感測器讀出電路設計與實現

Abstract

在本篇論文中，我們使用時脈-數位轉換器(TDC)分別實踐於兩種不同的讀出電路。相對於傳統的類比-數位轉換器，我們先將類比訊號轉換成時脈，進而直接轉換成數位碼讀出。第一種TDC的實現電路為差動式電容轉數位讀出電路。差動式讀出電路只會轉換差模電容之間的變異情形，而可直接忽略雙端共模電容的變化。另一種TDC的實現電路為應用在單端輸出感測器的雙延遲鎖相迴路式(dual-DLL)時脈轉數位讀出電路。這類單端輸出感測器具有較大的寄生電容，因此dual-DLL讀出電路補償了寄生電容，並藉由自動矯正機制來增加感測範圍。在電路的應用上，分別針對不同的環境感測器，我們的差動式電容轉數位讀出電路可適用在雙端差動指叉電容式加速度感測器，而dual-DLL時脈轉數位讀出電路則可適用在單端感測器，例如：濕度計與溫度計。從晶片的量測結果中可得到，我們所設計的差動式讀出電路以單軸加速度為例，可操作在125K赫茲的取樣頻率下，可分辨出80個層級共±8g的加速度差異，並且消耗約50uW的功率。我們使用的是聯電0.18μm CMOS製程。另外在濕度計的量測中，在操作模式下有52μW的功率消耗，而在休眠模式下則只有13μW的功率消耗。我們所使用的取樣頻率為8K赫茲以及使用台積電0.35μm CMOS製程。由量測結果可顯示，本論文所提出的電路具有低功耗與高解析等優點。

In this thesis, we present two types of readout circuits by using time-to-digital convertors (TDC). In contrast to traditional analog-to-digital converter (ADC), our approach converts the analog signal into the time pulse, and directly outputs the digital code without the voltage-to-digital or current-to-digital converter. The first type of TDCs is the differential capacitance-to-digital readout circuit. The differential readout circuit only converts the variation of differential capacitance and ignores the common-mode capacitance. Another type of TDCs is dual-DLL time-to-digital readout circuit. This circuit is used to the sensors with single-ended output. These sensors have large parasitic capacitances, and this readout circuit can compensate the parasitic capacitance and increase the sensing range with an auto-trimming mechanism. To implement the environmental sensor with our readout circuits, the differential capacitance-to-digital readout circuit is used in an accelerometer with differential finger-type electrodes. And dual-DLL time-to-digital readout circuit is used in the single-ended output sensors, humidity sensor and temperature sensors. From chip measurement results, our accelerometer can differentiate the 80-level accelerations between ±8g, and just consumes around 50uW for 1-axis, 82uW for 3-axis under 125KHz of sampling frequency with 1.8v of supply voltage. The humidity sensor is 52uW in the operating mode, and 13uW in the sleeping mode under 8KHz of sampling frequency with 1.3v of supply voltage.