Biopotential signals are important to physicians for diagnosing medical conditions in patients. Traditionally, biopotentials are acquired using contact electrodes together with instrumentation amplifiers (INAs). The biopotentials are generally weak and in the presence of stronger common mode signals. The INA thus needs to have very good Common Mode Rejection Ratio (CMRR) to amplify the weak biopotential while rejecting the stronger common mode interferers. Opamp based INAs with a resistor-capacitor feedback are suitable for acquiring biopotentials with low power and low noise performance. However, CMRR of such INA topologies is typically very poor. In the presented research, a technique is proposed for improving the CMRR of opamp based INAs in RC feedback configurations by dynamically matching input and feedback capacitor pairs. Two instrumentation amplifiers (one fully differential and the other fully balanced fully symmetric) are designed with the proposed dynamic element matching scheme. Post layout simulation results show that with 1 percent mismatch between the limiting capacitor pairs, CMRR is improved to above 150dB when the proposed dynamic element matching scheme is used. The INAs draw about 10uA of quiescent current from a 1.5 dual power supply source. The input referred noise of the INAs is less than 3uV/sqrt(Hz).

Electro-Magnetic Interference(EMI) degrades the perfomance of electronic systems. So, Amplifiers which are the basic building blocks used in the front-end of analog and mixed-signal Integrated Circuits (ICs) must be evaluated for EMI. This work introduces the most intriguing figure of merit, Electro-Magnetic Interference Rejection Ratio (EMIRR) to measure the EMI immunity of precision Instrumentation Amplifiers (INAs) that helps to select the EMI robust INAs for EMI critical applications. In this work, a new EMIRR measurement setup is implemented to measure the immunity of INAs for conducted EMI ranging from 10 MHz to 3 GHz. The shift in the DC offset voltage generated at the output of the INA due to RF rectification, is used to compute EMIRR. As part of the setup, the hardware evaluation board is designed and an automation test software is developed to run EMIRR measurements. Furthermore, EMIRR measurements are performed on several INAs with different specifications to compare and rank them on their EMI immunity levels. Additionally, with the help of EMIRR metric, suitable INAs for developing EMI-sensitive applications are proposed. Finally, the influence of amplifier bandwidth, the input capacitance, 50 Ω termination at the end of RF input trace, INA package parasitics and EMI filter bandwidth on EMIRR is analyzed with the measurement results.