How to reduce internal crosstalk in an electrical force measurement switch (PMS)?

When digital circuits (such as MCUs and CPLDs) coexist with analog measurement circuits and power switch drive circuits in a limited space within a PMS, the electromagnetic field generated by the edges of high-speed signals can couple to sensitive circuits through PCB traces, power planes, or spatial radiation, causing crosstalk. This manifests as measurement values fluctuating with switching actions. Reducing crosstalk requires addressing three aspects: isolation, filtering, and layout.

First, implement strict PCB partitioning: place the digital, analog, and power areas in different regions, separated by an isolation strip of at least 3mm, and use a CMZ20212A-900T common-mode inductor (900μH) to bridge the digital and analog power supplies to form filtering isolation. Critical signal lines (such as clock and PWM) should use striplines or embedded microstrip lines and be wrapped with ground lines.

Second, connect a PBZ1005B-501Z0T ferrite bead (500Ω@100MHz) in series with all high-speed I/O ports or connect an ESD5V0D8B electrostatic discharge protection diode (Cj<3pF) in parallel at the source end to slow down the rise time and absorb high-frequency harmonics.

Finally, simulation optimization of the stack-up ensures a complete ground plane serves as the return path. Experimental results show that the above method can reduce digital noise interference to the 16-bit ADC to below 1 LSB, and the system's radiated emissions meet the EN 55032 Class B limits.