Patent ID: 7587442

Claim:
A method of determining a phase-corrected derivative of a noise-containing input signal, comprising the step of: periodically sampling the input signal to form a data stream of successive input signal values; determining a normal derivative of the input signal based on a rate of change with respect to time between successive input signal values separated by a time interval Δt, and updating said normal derivative at the time interval of Δt to form a first data stream of normal derivative values; determining an aliased derivative of the input signal based on a rate of change with respect to time between successive input signal values separated by an increased interval of an integer R times the time interval Δt, and updating said aliased derivative at the increased interval to form a second data stream of aliased derivative values; low-pass filtering said first data stream of normal derivative values to form a derivative output; and periodically resetting said derivative output to a reset value based in part on said second data stream of aliased derivative values, wherein the resetting removes a phase delay in the first data stream introduced by the low-pass filtering to create the phase-corrected derivative.