Immunity of Analog Devices against Continuous Radio-Frequency Disturbances

The immunity of analog devices against continuous radio-frequency (RF) disturbances is discussed in this paper, where operational amplifier (OA) circuits are used as examples. To evaluate their immunity, sinusoidal signals were injected to various locations on the OA circuits with output offsets monitored. The test results show that the two OA inputs are the most sensitive ports, but actual circuit topologies affect the outcomes dramatically. When the OA circuits become part of circuit boards or larger systems, the system-level parameters like mutual coupling and resonances also substantially alter the results. To demonstrate these phenomena, circuit examples ranging from bare-bone OA circuits to boards with harnesses are presented. The basic immunity mechanisms are explained by simple circuit models, more complicated phenomena are computed by numerical simulation, and all are verified by test results with detailed discussion / explanation.