EMI Susceptibility In Analog Circuits
by Walter Bacharowski, Staff Applications Engineer, National Semiconductor Corporation
The widespread and growing use of portable wireless communications devices has added additional circuit complexity and testing requirements to all electronic equipment, any of which has the possibility of being exposed to strong RF fields. While some RF fields may be strong enough to cause physical damage and failure of the exposed circuits, in the majority of cases the electronic circuitry continues to perform but experiences a shift from its normal operating point. The operating point shift by itself will not damage the circuitry but its effect on the system that the circuit is a part of can cause range of problems. An example of an irritating, but not serious, effect is the buzzing caused by cell phones in close proximity to audio equipment. On the other hand, the effect on the speed control loop of an electric wheelchair could cause erratic acceleration and deceleration and might be dangerous for the wheel chair occupant. This TechNote describes and demonstrates the shifted operating point of an analog circuit and introduces new amplifier designs that contribute to mitigating the shifted operating point.
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