| Summary: | 碩士 === 中原大學 === 電子工程研究所 === 93 === Ion Sensitive Field-Effect Transistor had been a hot research topic in the past 30 years. Research indicting ISFET have some drawbacks such as temperature effect, drift and hysteresis. These factors limit the accuracy of ISFET signal extraction. Moreover, the accuracy of the signal readout is greatly improved based on a large number of sensors. ISFET-based sensor array on biological application is also a trend.
This thesis first explored the cause of pH sensitivity loss of the source follower configuration readout circuit. The improvement present a 4 by 2 ISFET sensor array system based on a bridge-type floating source readout interface. Due to the different DC level and temperature coefficient of each sensor in the array, the compensation methods have been proposed. Experimental results present the improvement of pH sensitivity in source follower readout circuit, temperature compensation and output DC level to 13%, 36% and 97.3%, respectively.
Furthermore, an ISFET behavioral macromodel take into account non-ideal drift effects have been developed. These models were then used to design bridge-type floating source interface circuit. The modeled-versus-measured fit of the dependence of drift rate on long time period, temperature and different pH value present a RMS error of 2.2%, 2.4% and 6.6%, respectively. The developed macromodel can be adapted to speed up the design of silicon-based chemical-microsystem.
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