How to control the minimum loop of the electrical force measurement switch (PMS) measurement circuit?

The larger the loop area of the PMS measurement loop (especially current sampling), the easier it is to pick up interference from alternating magnetic fields in space (such as those from power transformers and switching transistors), inducing noise voltage. Controlling the minimum loop area is key to improving the signal-to-noise ratio. For current sampling, surface-mount shunt resistors should be used instead of through-hole resistors, and differential sampling lines (such as + and -) should be routed closely and in parallel on the PCB, preferably on adjacent layers and aligned vertically to form a microstrip line structure. Connect the input pins of the differential amplifier directly to the two ends of the sampling resistor, without running long wires in between.

If a current transformer (CT) must be used, the secondary output lines should be twisted before entering the PCB. For voltage sampling, the voltage divider resistor should be placed close to the ADC input pins, and the loop formed between the upper end of the voltage divider network and the ground should be minimized. All sampling loops should have a complete ground plane as a mirror return plane. Through design, the area of a typical current sampling loop can be reduced from 100 mm² to less than 10 mm², thereby reducing space magnetic field induced noise by 20 dB. This ensures that the ripple of the sampled signal is less than 1 LSB of the ADC in strong interference environments.