How to ensure EMC of differential signals in motion controller MC encoders

Ensuring the EMC performance of the differential signal from the motion controller's MC encoder requires guaranteeing signal integrity throughout its generation and reception. The differential drive on the encoder side must be balanced, with consistent output amplitude and opposite phase. Transmission uses impedance-matched twisted-pair shielded cable, with the shield grounded at the controller end. A differential receiver with high common-mode rejection ratio (CMRR) is used at the controller interface. Common-mode chokes are added to each signal pair to further suppress common-mode noise. A low-capacitance TVS diode array is connected in parallel for transient protection.

On the PCB, differential receiver traces are strictly equal in length and spacing, and reference a complete ground plane. Sufficient decoupling is necessary to avoid the influence of receiver power supply noise. Verification is achieved through testing: measuring the common-mode noise margin of the differential signal; injecting common-mode interference into the line and observing for counting errors; and performing radiated emission testing to ensure the interface itself does not generate excessive radiation. For high-resolution encoders, even minor interference can lead to counting errors; therefore, EMC design must be exceptionally rigorous.