ISFET Sensor And The Design Of Mulit-route Measure System

Because of broad scope of ion measurement of ISFET (ion-sensitive field-effect transistor) , ISFET is widely used such as environmental protection, chemical industry, mining area, geology, earth, hydrology, and family, and so on. Especially distinguishing feature of miniature, ISFET not only is used widely in biology medical service field, but also is strongly vitality, So ISFET biology sensor and multi-route measurement system are our important necessaries. ISFET has been the object of many research activities. Nevertheless, the threshold voltage time dependence, noise and the technological difficulties associated with the packaging of miniature reference electrodes limit the commercial viability of all the ISFET application. In the last years, in order to overcome these drawbacks, different approaches have been pursued, such as on-ehip fabrication of electrode with micro-fabrication techniques, as well as physical and chemical treatments of the sensing membrane. But the result does not very satisfy'us. Thus I choose differential arrangement to overcome these drawbacks, consisting of an ISFET and a reference FET(REFET), a noble metal counter-electrode provides the electrical contact to the test electrolyte.Fust of all I detailedly introduce rules of ISFET sensor and discuss its method of measurement based on rules, so I choose deferential arrangement. Then I design ISFET buffer amplifier and analyse its noise. Considering its area of sensitive film and its noise, I decide breadth and length of gate of ISFET, separately 800 micron and 20 micron. And I simulate it with HSPICE of Synopsy corporation and 0.6 micron process of ShangHua corporation. Its equivalent input noise volt is 0.32 microvolt from 0.05Hz to 250Hz, jroise volt peak value is 1.9 microvolt. Its work loss is 850.7 micro- watt. Output noise volt is 2.8 microvolt, corresponding to a resolution of 1/20 p .Due to differential output, its noise is rejected partly, so its resolution largely is improved. Because of low power we may integrate 32 the seniors. At last we sample 32 route biology signal by four double 8 change-over switch CC4097, a apparatus instrument amplifier INA110, a wave filter MAX297, a analog-digital converter A/D678 and programming fixed time or . counter 8253, In order to advance it, I adopt DMA(direct memory access) technology and replace memory technology. We can sample about six points during a cycle. And this system completely accords with sampling rule.The method largely resolves the problem which has- puzzled us chronically andeasily makes ISFET and measurement system commercial viability.