Signal Attenuation
Electronic conditioning circuitry attenuates high frequency signal components while allowing lower frequencies to pass through unchanged. An analog low pass filter accomplishes this frequency selection prior to digitization to prevent aliasing in analog to digital converters. The threshold of this action is the cutoff frequency where the signal power drops by three decibels.
Cutoff Characterization
Mathematical approximations define how the transition band behaves between the passband and the stopband. A Butterworth design offers a maximally flat response in the passband, whereas a Chebyshev design introduces ripple to achieve a sharper transition. These characteristics determine the attenuation rate of unwanted frequencies.
Phase Response
Signal propagation delay varies across the frequency spectrum depending on the filter type. Non-linear phase shifts occur near the cutoff frequency, introducing distortion in time-domain signals such as pulses. A Bessel response minimizes this distortion by maintaining a constant group delay in the passband.
Circuit Topology
Passive networks use combinations of resistors and capacitors to achieve the desired filtering without external power. Active designs instead incorporate operational amplifiers to provide gain and isolate stages, eliminating the need for bulky inductors. These active configurations are limited by the bandwidth and slew rate of the operational amplifier.
When integrating these circuits into precise measurement systems, design engineers must select low noise amplifiers to prevent the degradation of weak sensor outputs.
