How can differential mode filtering in an intelligent low-voltage monitoring unit not affect monitoring accuracy?

Differential-mode filtering requires a low-distortion design to avoid affecting monitoring accuracy. Current sampling uses a differential input active filter with an AD8629 operational amplifier, a cutoff frequency of 2kHz, and a common-mode rejection ratio greater than 100dB. Voltage sampling uses an RC filter (100Ω + 10nF) with a time constant of 1μs, coupled with ESD protection (3V3D3B). PCB design: The filter circuit is placed close to the sensor, using differential traces with 100Ω impedance matching. C0G capacitors are used, with a temperature coefficient of ±30ppm/℃. This design ensures that the differential-mode filtering affects the amplitude of the monitored signal by less than 0.05%, the phase delay by less than 0.5°, and noise suppression by more than 25dB, meeting the IEC 61869 standard's 0.5 accuracy requirement.