Transconductance Converters Based on Current Mirrors Applied to pH Measurement Using ISFET Sensors

New transconductance circuits (V/I converters) are designed based on current mirrors and operational amplifiers. Their input/output characteristics and the influence of DC parameters are obtained. Experimental results were performed, comparing them with the simulated results. An electronic instrumentation circuit is designed based on one of the transconductance converters analyzed. The purpose of this circuit was to condition the response of an ion-sensitive field-effect transistor (ISFET) to measure pH. In the proposed application, the V/I converter presented provides the stability and accuracy of the ISFET operating point, making an easy characterization procedure and the design of multichannel ISFET-based measurement systems possible. Experimental results of the ISFET main electrical parameters were obtained, showing the feasibility of applying these new converters to instrumentation and electrochemical measurements.