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.
Carrier Frequency Rejection
Demodulation Attenuation
Signal recovery stages following inductive or capacitive sensor interfaces process amplitude-modulated excitation signals to extract baseband physical measurements. Carrier frequency rejection defines the degree to which residual carrier tone energy is suppressed relative to the recovered baseband signal. Insufficient attenuation allows residual carrier voltage to overload high-gain downstream analog-to-digital converters.
Spectrum analyzer measurements verify suppression performance across the full operational bandwidth of the signal conditioning chain.
Filter Notch
Active low-pass or band-stop filter networks remove excitation fundamentals while passing low-frequency sensor data. Achieving high carrier frequency rejection requires high-order active filter topologies with narrow notch bandwidths. Temperature drift in component values shifts the notch frequency away from the excitation carrier, reducing attenuation.
Phase Unbalance
Double-balanced demodulator structures cancel carrier feedthrough when upper and lower signal paths maintain exact amplitude and phase symmetry. Imbalance in balance transformers degrades carrier frequency rejection by allowing unmodulated carrier current to bleed into the output node. Matching trace impedances minimizes high-frequency phase imbalance across the demodulator.
Residual Carrier
Residual voltage components create offset errors and ripple in DC measurement channels. Measuring carrier frequency rejection under maximum input amplitude conditions confirms system headroom. Filter design adjustments prevent carrier feedthrough from saturating digital acquisition stages.