生醫感測系統之電流式混模信號處理器設計

A Novel Mixed-Mode Signal Processor Design by Current-Mode Circuits for Biomedical Sensing System

鄭少鈞(Shao-Chun Cheng)

指導教授 ： 鍾文耀

中原大學/工學院/電子工程研究所/碩士(2009年)

https://doi.org/10.6840/CYCU.2009.00839

摘要

本研究之目的在於提供多種生理參數感測皆適用之電流式生醫感測系統，主要是針對電流式感測器做訊號處理，用以感測人體之相關生理參數，如葡萄糖、尿酸等，皆適用此電流式生醫感測系統。
整體系統包含恆電位儀、電流比較器與電流導管式類比至數位轉換器三部分，與其他論文不同點在於全系統皆以電流式電路所構成，不需將感測到的電流信號轉成電壓信號後再傳至電壓式類比數位轉換器。其優點為為可應用在低電壓系統內，由於電流式電路之輸出信號非電壓(輸出信號為電流)，輸出信號範圍不受電源電壓大小之限制。
本研究之另一項重點在於提高系統之電流的感測範圍，以達到葡萄糖感測(感測電流較大)與尿酸感測(感測電流較小)等皆可使用相同的系統。第一部分為承接感測器信號之新型恆電位儀讀出電路，其電流感測範圍為250 pA~80 μA。第二部分為新型電流比較器，此為第三部分電流導管式類比至數位轉換器之核心，其設計重點為提高電流比較器之精準度，其輸入電流與參考電流相差低至0.6 nA時，電流比較器仍可正確判斷電流大小。提高電流比較器之精準度可同時提高電流導管式類比至數位轉換器之解析度，以達到大感測電流範圍之目的，使本研究可應用之生醫感測種類更廣泛。
全系統採用國家晶片系統設計中心TSMC 0.35 μm Mixed-Signal 2P4M Polycide 3.3V/5V製程下線製作，並使用下線後之晶片完成葡萄糖感測之實際量測，信號分析與記錄部分使用LabVIEW人機介面記錄葡萄糖信號並分析其線性度。

關鍵字

電流式 ； 生醫感測系統 ； 恆電位儀 ； 電流比較器 ； 類比至數位轉換器

並列摘要

The purpose of this research is to design a biomedical sensing system which can sense different kinds of physiological parameters (e.g. glucose, uric acid, etc.). The described system utilized amperometric sensor to measure the physiological parameters which is designed using current-mode circuits.
The biomedical sensing system consists of three sub-circuits: 1) potentiostat, 2) current comparator, and 3) current-mode pipeline ADC (analog to digital converter). The sub-circuits were implemented using current-mode circuits, making this research different from others. Some researches used different methods in which the input current is still to be converted to output voltage then use the voltage-mode ADC. This work, however, uses input current signals directly eliminating the need for converting current signals to voltage. The highlight of this research is the implementation of the sensing system which made it more suitable for low voltage system. Since the output signal is current, the range of output is not limited by low voltage power supply.
Another advantage of this research is its wide dynamic range of sensing current. This is used to simultaneously sense both glucose level (large sensing current) and uric acid level (small sensing current). The first stage of this system is a novel potentiostat readout circuit which can sense current from 250 pA to 80 μA. The second stage is a novel current comparator which is the core of the third stage of this system. The advantage of the novel current comparator is its high accuracy, in which the differential current of the current comparator can be as small as 0.6 nA and still maintaining a valid output on the current comparator. Increasing the accuracy of current comparator will also increase the resolution of current mode ADC. Therefore, the system can sense more kind of physiological parameters.
The whole system is implemented using TSMC 0.35 μm Mixed-Signal 2P4M Polycide 3.3V/5V process of National Chip Implementation Center (CIC), Taiwan. The chip was tested by measuring the glucose level of the glucose solution. The signal linearity were measured, analyzed and recorded using LabVIEW.

並列關鍵字

Analog to digital converter ； Current-mode ； Biomedical sensing system ； Current comparator ； Potentiostat

參考文獻

[1] "World Health Organization," http://www.who.int/en/

[2] Y. Yang, S. F. Zhang, M. A. Kingston, G. Jones, G. Wright, and S. A. Spencer, "Glucose sensor with improved haemocompatibilty," Biosensors and Bioelectronics, vol. 15, pp. 221-227, 2000.

[3] L. Clark, "C. Lyons. Electrode systems for continuous monitoring in cardiovascular surgery," Ann. N. Y. Acad. Sci, vol. 102, 1962.

[4] G. G. Guilbault and G. J. Lubrano, "An enzyme electrode for the amperometric determination of glucose," Anal Chim Acta, vol. 64, pp. 439-455, 1973.

[6] J. E. Frew and H. A. O. Hill, "Electrochemical biosensors," Analytical Chemistry, vol. 59, pp. 933-944, 1987.