A digital control unit for electro-hydraulic servo valves featuring high-precision control and integrated LVDT digital demodulation

This paper proposes an intelligent control unit of electro-hydraulic servo valves with high performance, which has a new digital architecture in place of the traditional analog circuits. The key innovations are the custom-designed numerical control circuit and a digital demodulation technique based on FPGA to Linear Variable Differential Transformer (LVDT) feedback signals. Using synchronous square-wave demodulation and orthogonal dual-channel processing, the system successfully removes phase-shift-induced errors without using temperature-sensitive analog multipliers. All the signal excitation, precision demodulation, and advanced servo algorithms including backstepping control are incorporated into a small, modular PCB stack that provides a steady-state position accuracy of better than 0.5% and microsecond-level dynamic response. Experimental results under sinusoidal tracking commands (4 V amplitude, up to 30 Hz) demonstrate excellent tracking fidelity and robustness. The design offers a reliable, high-precision digital alternative to traditional analog servo valve control.