EMI Rejection Ratio of Operational Amplifiers

This application report introduces the concept of electromagnetic interference rejection ratio (EMIRR IN+) as a measure of the immunity of an operational amplifier to responding to electromagnetic interference (EMI). Texas Instruments has developed the ability to accurately measure and quantify the immunity of an operational amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. Definitions, equations, and example calculations of EMIRR IN+ are provided, as well as a discussion of how to measure EMIRR IN+. EMI coupling and RF circuit concepts are also reviewed for the reader’s benefit. This report shows the reader how to apply the EMIRR IN+ parameter when EMI is a concern in a given circuit design. The EMIRR IN+ parameter is now being tested for all new and many existing operational amplifiers available from Texas Instruments.