應用於血糖監測之無線供電式電流類比數位轉換器

A Wirelessly-Powering Current-Mode Analog-to-Digital Converter for Blood Glucose Monitoring

曹舒堯(Shu-Yao Tsao)

指導教授 ： 蔡宗亨 ； 廖育德

國立中正大學/工學院/電機工程學系/碩士(2015年)

摘要

糖尿病是二十一世紀罹患率增加最快的慢性疾病，2013年全球罹患糖尿病的人數已高達3億8200萬人。而且，在台灣糖尿病位居102年國人十大死因第四名。為了維持血糖的穩定，糖尿病患必須長期自我檢測血糖。此外，近年來生醫晶片越來越受歡迎，因為它可以整合感測、訊號處理和無線傳輸在一個微小晶片上，易於攜帶以及可以達到即時監控。
血糖試紙的原理是葡萄糖與酵素的生化反應進而產生氧化電流。根據電流的大小可以對應出血液中葡萄糖的濃度。本論文提出一個應用於血糖監測之無線供電式電流類比數位轉換器，以CMOS 0.18um製程來實現。系統中採用電流式類比數位轉換器來直接轉換氧化電流成為數位碼。相對於電壓式類比數位轉換器，電流式類比數位轉換器不需要電流轉電壓的轉換器，所以較不容易引入雜訊和較寬的動態範圍。加上，電流式類比數位轉換器沒有用到電容陣列，可以達到小面積，進而節省製作成本而且易於攜帶。由於本系統將會結合電子紙來顯示轉換後的血糖值，所以整體電路的功率消耗不可以太大。因此，在類比數位轉換電路上，採用連續逼近式架構來實現。
此研究有對市售的血糖試紙所做的葡萄糖濃度與電流特性的實驗，根據實驗結果決定了1~3uA為電流式類比數位轉換器的輸入電流範圍。本論文呈現一個低功率9位元且取樣頻率為20KS/s的連續逼近式電流類比數位轉換器。當供應電壓為1.3伏特且輸入訊號頻率為2KHz時，由佈局後的模擬結果可得知，訊號雜訊失真比為46.9dB，有效位元為7.5位元。當供應電壓為1.6伏特且輸入訊號頻率為1.5KHz時，由量測的結果可得知，訊號雜訊失真比為26.96dB，有效位元為4.19位元。

關鍵字

低功率設計 ； 連續逼近式類比數位轉換器 ； 電流式類比數位轉換器 ； 血糖監控

並列摘要

Diabetes is one of the popular chronic diseases in the twenty-first century. Global diabetes population roams up to three hundred eighty two million, and diabetes are ranked as the fourth in the top ten causes of death in Taiwan in 2013. To maintain stable blood glucose, the diabetic patients need the long-term monitoring of their blood glucose. A solution using biomedical chip for glucose monitoring is attractive in recent years. The chip integrates signal processing, sensing, and wireless transmission capabilities in a tiny chip, which make it portable and real-time monitoring.
The principle of the blood test strip is the biomedical reaction between the glucose and the enzyme to produce the oxidation current. The glucose concentration can be known because the current is proportional to the glucose concentration. This thesis proposes a wirelessly-powering current-mode analog-to-digital converter for blood glucose monitoring which is realized in CMOS 0.18um technology. The current-mode ADC is adopted to convert the oxidation current directly. Compared to the voltage-mode ADC, the current-mode ADC doesn’t need a current-to-voltage converter so it has the less induced noise and wide dynamic range. Moreover, the area of the current-mode converter is smaller than voltage mode implementation due to no required capacitor array, so the fabrication cost can be reduced. The proposed system will combine an electronic paper to display the blood value that directly converted by the current-mode ADC. Thus, the successive approximation (SAR) architecture is employed in the analog-to-digital converter for energy efficiency.
The research includes the experiment of the commercial glucose test strip. The current input range of the current-mode ADC is decided in the range of 1~3uA as our design specification according to the experimental results. The post-layout simulation result of the proposed current-mode ADC at a 20 KS/s sample rate can achieve 46.9dB SNDR and 7.5 bit ENOB with a 2KHz input frequency while the voltage supply is 1.3V. The measured result can achieve 26.96dB SNDR and 4.19 bit ENOB with a 1.5 KHz input frequency while the voltage supply is 1.6V.

並列關鍵字

Low-Power Design ； Successive Approximation Analog-to-Digital Converter ； Current-Mode Analog-to-Digital Converter ； Blood Glucose Monitoring

參考文獻

[4] E. Maghsoudloo, S. Moradi, and A. Arian. "Current mode sensor interface system for biomedical implantable applications." Electrical Engineering (ICEE), IEEE 20th Iranian Conference, 2012.

[5] R. Dlugosz, and K. Iniewski. "Ultra low power current-mode algorithmic analog-to-digital converter implemented in 0.18 um CMOS technology for wireless sensor network." Mixed Design of Integrated Circuits and System, Proceedings of the International Conference, 2006.

[6] R. Długosz, and K. Iniewski. "Flexible architecture of ultra-low-power current-mode interleaved successive approximation analog-to-digital converter for wireless sensor networks." VLSI Design 2007 (2007).

[7] R. Długosz, V. Gaudet, and K. Iniewski. "Flexible ultra low power successive approximation analog-to-digital converter with asynchronous clock generator." Proceedings of the Canadian Conference on Electrical and Computer Engineering (CCECE). No. EPFL-CONF-167719. 2007.

[8] B. Haaheim, and T. G. Constandinou. "A sub-1uW, 16kHz current-mode SAR-ADC for single-neuron spike recording." IEEE International Symposium on Circuits and Systems, ISCAS, 2012.