| 摘要 |
PURPOSE:To achieve a higher measuring accuracy of ion concn., by stabilizing a potential of a comparison electrode with a false electrode 14 earthed. CONSTITUTION:A false electrode 14 is immersed into a liquid M to be measured while being earthed to maintain a reference potential VG almost at a constant value. A semiconductor device 10 has an ISFET 11 which detects an ion activity of the liquid M being measured to be outputted as source potential VS+VG and a temperature element 13. A comparison electrode 12 adds own potential VR to the reference potential VG to detect a liquid potential VR+VG. A liquid potential compensation circuit 55 compares the source potential VS+VG with the liquid potential VR+VG and outputs a compensation ion activity signal VS-VR. A constant current circuit 50 runs a drain current of ¦Id/beta¦<=0.10vol.t<2> when channel characteristic of the ISFET 11 represented by beta and the drain current Id. |
