Making portable electro-medical devices cheaper with EMI-immune ICs

Pacemaker users are generally advised to avoid places that are prone to high electromagnetic interference (EMI). Pacemakers use high-quality radio frequency (RF) shields to protect them from EMI; however, this adds to the cost of the device.

If Anjan Kumar Pudi, a research scholar with the IITB-Monash Research Academy has his way, this will hopefully change.

Anjan Kumar is working on a project titled, ‘Highly EMI-immune low-noise nano scale integrated circuits for portable electro-medical and electro-sensor applications’ under the supervision of Prof Maryam Shojaei Baghini and Prof Jean-Michel Redouté. His aim is to analyse existing topologies to identify where noise and electromagnetic compatibility issues originate, and then figure out ways to overcome these constraints using low power novel designs useful for a broad range of applications.

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

“Today’s pacemakers with Operational Amplifiers (OpAmps) that are non-EMI-immune, use a high-quality radio frequency (RF) shield to protect the device from changing its normal operation,” explains Anjan Kumar. “If we deploy circuits that are already EMI-immune by design, then we can either use a low-quality RF shield or completely remove the shield itself. This will also reduce the cost of the pacemaker.”

Electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking it with barriers made of conductive or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the ‘outside world’, and to cables to isolate wires from the environment through which the cable runs. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as RF shielding.

Reduction of DC operating point of an OpAmp due to the increasing EMI-amplitude.

“Circuits such as OpAmps, current mirrors, bandgap references, etc. — which are used in signal processing circuits, control circuits, and instrumentation — are constantly prone to EMI,” says Anjan Kumar. “At high frequencies, due to the EMI, the operating point of these circuits change. Due to this, the subsequent circuits in the chain do not work correctly. I am hoping to reduce this effect using circuit techniques. So far, research in this field has concentrated on making EMI-immune OpAmps. Some existing OpAmp architectures reduce offset, but for a limited frequency range only. No solutions have been proposed to reduce offset for the entire high frequency range (1MHz to 1GHz).”

Says Prof Murali Sastry, CEO of the Academy, “To describe the offset behaviour of circuits using mathematical modeling and also to propose a solution using the model is quite challenging. In the bio-medical area where these circuits are used, it is vital that these devices work efficiently under all probable conditions. If Anjan Kumar Pudi succeeds in his project, it could lead to a significant reduction in the price of portable electro-medical devices like pacemakers.”