Extended Gate H+-Ion Sensitive Field Effect Transistor with Signal Interface

Abstract

H + -ion concentration into digital form. This chip, fabricated in a 0.18-um CMOS 1P6M process, operated at a 1.8V supply voltage and normal sampling rate of 6.25MHz. The circuit (without pad) occupied an area of 0.66mm × 0.43mm. The experimental data showed that this structure has a linear pH response about 97 digital counts/pH in the ion concentration range between pH2 and pH12, and the gain errors within the H + -ion concentrations are less than 3%. The minimum detectable pH value can reach as small as ±0.25pH.