Design of a CMOS potentiostat circuit for electrochemical detector arrays.

High-throughput electrode arrays are required for advancing devices for testing the effect of drugs on cellular function. In this paper, we present design criteria for a potentiostat circuit that is capable of measuring transient amperometric oxidation currents at the surface of an electrode with submillisecond time resolution and picoampere current resolution. The potentiostat is a regulated cascode stage in which a high-gain amplifier maintains the electrode voltage through a negative feedback loop. The potentiostat uses a new shared amplifier structure in which all of the amplifiers in a given row of detectors share a common half circuit permitting us to use fewer transistors per detector. We also present measurements from a test chip that was fabricated in a 0.5-mu m, 5-V CMOS process through MOSIS. Each detector occupied a layout area of 35 mu m x 15 mu m and contained eight transistors and a 50-fF integrating capacitor. The rms current noise at 2-kHz bandwidth is approximate to 110 fA. The maximum charge storage capacity at 2 kHz is 1.26 x 10(6) electrons