Phase-sensitive demodulation of an LVDT's amplitude-modulated carrier produces sum and difference frequency components (carrier ± modulating frequency) that a low-pass filter must attenuate, with filter order and time constant chosen to meet a ripple-rejection tolerance while successive stages are impedance-matched (each roughly ten times the next) to avoid loading; a related design fact is that an LVDT circuit has a specific excitation frequency at which input-output phase shift is exactly zero, found by setting the transfer function's imaginary (quadrature) term to zero. This belongs to signal-conditioning and filter-design theory in industrial instrumentation, extending modulation, RC filtering, impedance-matching, and op-amp loading principles already established for LVDTs and other sensors.
Phase-sensitive demodulation of an LVDT's amplitude-modulated carrier produces sum and difference frequency components (carrier ± modulating frequency) that a low-pass filter must attenuate, with fil…