Ramp-tracking anti-aliasing and anti-imaging filter for control instrumentation

A novel analog lowpass filter with predictive characteristics is proposed for anti-aliasing and anti-imaging filtering in instrumentation, signal processing, and automatic control. The filter is capable of following a ramp input without causing delay on the primary signal in steady-state operation. Such filtering is advantageous in several industrial applications; for example, many real-world velocity signals are piece-wise first-order polynomials. The filter has lowpass characteristics, an almost equiripple passband, and a high stopband attenuation. A prototype of the sixth-order filter was constructed using active-RC techniques, and demonstrates the ramp-tracking capability as well as the lowpass characteristics. The demonstrator filter has a 30 Hz passband width and 20 dB attenuation at 50 Hz