CURRENT-MODE INSTRUMENTATION AMPLIFIERS USING 0.25µM CMOS PROCESS FOR ECG SIGNALS

Four monolithic current-mode instrumentation amplifier (in-amp) topologies implemented in a standard 0.25µm complementary metal-oxide semiconductor (CMOS) process, with positive second-generation current conveyors (CCII+) as building blocks are presented in this paper.  The in-amp topologies are designed to handle biomedical signals, specifically that of the electrocardiogram (ECG). Four types of CCII+ are characterized and realized using a rail-to-rail operational amplifier (op-amp) and different types of current mirrors.  The Op-Amp with Simple Current Mirror exhibits the highest current swing and the lowest power consumption, and is thus chosen as the optimum CCII+ block to be used in all four in-amps.   All current-mode in-amps yield excellent common-mode rejection ratio (CMRR) greater than 150dB for a differential gain of 100. The in-amps consume less than 2.5mW of power for a single voltage supply of 2.5V.  However, the 2-Current Conveyor with Op-Amp at the Output (2-CC with Op-Amp) has adjustable output reference voltage and provides the lowest output impedance among the four in-amps.