Multi Coil Quadrature Demodulation Signal Chains for Proximity Measurement
Multi coil quadrature demodulation isolates amplitude and phase in inductive proximity chains, resolving sub-micron targets while rejecting thermal noise.
Phase Sensitive Detector
Synchronous Demodulation Instrument
Signal extraction from extreme noise environments is achieved by multiplying an input waveform with a reference signal of the same frequency. A phase sensitive detector acts as a narrow band filter that ignores all signals not coherent with its reference source. It allows for the measurement of nanovolt signals even when they are buried under volts of random noise.
Detection Mechanism
The circuit performs a mathematical multiplication of the sensor data and a local oscillator. Only the components that match the reference frequency and maintain a stable phase relationship produce a direct current output. Then the phase sensitive detector rejects white noise and harmonics of the power line.
Adjustment of the phase offset allows the operator to select either the resistive or the reactive part of the signal.
Operational Benefit
This metric quantifies the ability of the instrument to recover a signal from much larger background noise. Modern units provide a dynamic reserve of over one hundred decibels. Because the phase sensitive detector relies on a reference, it is immune to frequency drift in the signal source as long as the source provides the reference.
Filter Requirement
A low pass filter following the mixer removes the sum frequency components. The time constant of this filter determines the final bandwidth.