How to resist EMI in analog sampling of frequency converters

Improving the EMI immunity of inverter analog sampling is crucial for ensuring the measurement accuracy of key parameters such as current, voltage, and temperature. Analog sampling circuits are highly susceptible to switching noise interference. EMI mitigation measures include: implementing a hardware low-pass filter before the sensor signal enters the ADC, typically an active filter composed of RC or operational amplifiers, with a cutoff frequency slightly higher than the signal frequency but much lower than the switching frequency; performing fine decoupling on the operational amplifier's power pins using ferrite beads and MLCC capacitors; employing differential sampling and utilizing the high common-mode rejection ratio of the instrumentation amplifier; using shielded twisted-pair cables to connect the sensor, with the shield grounded at a single point on the inverter side; on the PCB layout, centrally placing the analog sampling circuitry in a quiet area and completely enclosing it with an analog ground plane, isolating it from the digital area via grounding trenches or ferrite beads; keeping sampling signal traces short and away from power lines and high-frequency signal lines; for high-precision ADCs, considering using an independent reference voltage source and strengthening filtering; and on the software side, using digital filtering algorithms for post-processing of the sampled data. The effectiveness of the anti-interference design is verified by testing the noise level of the sampling channel during inverter operation. The filtering and isolation solutions provided by Audiotech can be used to build highly robust analog sampling front-ends.