Design of CMOS instrumentation amplifier using gm/ID methodology

This paper describes the design of an indirect current feedback Instrumentation Amplifier (IA). Transistor sizing plays a major role in achieving the desired gain, the Common Mode Rejection Ratio (CMRR) and the bandwidth of the Instrumentation Amplifier. A g
_m
/I
_D
based design methodology is employed to design the functional blocks of the IA. It links the design variables of each functional block to its target specifications and is used to develop design charts that are used to accurately size the transistors. The IA thus designed achieves a voltage gain of 31dB with a bandwidth 1.2MHz and a CMRR of 87dB at 1MHz. The circuit design is carried out using 0.18μm CMOS process.