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.
Sallen-Key Low Pass Filter
Filter Topology
Signal conditioning stages situated between analog sensor transducers and analog-to-digital converters employ active filter topologies to attenuate high-frequency noise and prevent aliasing. A Sallen-Key low pass filter utilizes a single operational amplifier configured with positive feedback to implement second-order voltage-controlled voltage source filtering. Non-inverting operational amplifier configurations provide unity or moderate gain with high input impedance.
Network transfer functions depend on passive resistor and capacitor component values in the feedback loops.
Frequency Response
Component selections establish corner frequency and quality factor, defining response characteristics from Butterworth maximally flat passbands to Chebyshev ripple responses. In a Sallen-Key low pass filter, corner frequency scales inversely with resistance and capacitance products. Rolloff rates reach forty decibels per decade above the cut-off frequency.
Component Sensitivity
Tolerance variations in active and passive components cause cut-off frequency shifts and passband peaking. High quality factors increase Sallen-Key low pass filter sensitivity to capacitor drift over temperature changes. Precision metal film resistors and stable C0G ceramic capacitors preserve response shape across wide industrial operating ranges.
Amplifier Bandwidth
Limited operational amplifier gain-bandwidth products reduce high-frequency stopband rejection. Input capacitance degrades active filter stability at high frequencies. Selecting op amps with adequate gain margins preserves attenuation depth across the rejection band.