Susceptibility of Operational Amplifiers to Conducted EMI Injected Through the Ground Plane into Their Output Terminal

In practical printed circuit board (PCB) designs, electromagnetic interference (EMI) is coupled from the ground plane, which is commonly shared among the analog, digital, and mixed-signal integrated circuits. This noisy ground plane couples interference capacitively to all the IC pins, including the output: this effect is exacerbated when the IC is connected to long wires and traces that are routed close to the conductive ground plane. This paper reports on the effect of interference, which is coupled capacitively from the PCB ground plane into all the IC pins of an opamp connected as a voltage buffer. Simulations illustrate the susceptibilities in custom operational amplifier designs, and are corroborated by measurements on several commercial devices. These measurements show that the EMI-induced offset can attain considerable values for the most critical EMI frequencies, which lie between 10 and 100 MHz. Moreover, these illustrate that there is a considerable susceptibility of operational amplifiers to electromagnetic interference coupled to their output pins.