Patent ID: 7180940

Claim:
A 360 degree phase delay digital filtering system for filtering a digital sequence, the digital sequence being a sequence of samples from a frequency and amplitude varying input signal, comprising: a higher stopband attenuation slower transient response bandpass infinite impulse response filter (hereinafter called “High Q BP IIR filter”) and a lower stopband attenuation faster transient response bandpass infinite impulse response filter (hereinafter called “Low Q BP IIR filter”) each for accepting the digital sequence and for outputting a first and second filtered output respectively; the High Q BP IIR filter having a first state register and operating at a center frequency; an output phase shifter to delay the first filtered output to a total of one period of the center frequency as compared to the input signal; the Low Q BP IIR filter having a second state register and operating at the same center frequency; an intermediate phase shifter to synchronize the second filtered output to the first filtered output; a disturbance detector for comparing the first and second filtered outputs and for signalling a disturbance where the difference between the synchronized outputs is greater than a threshold level; a switch for replacing the contents of the first state register with the contents of the second state register when the disturbance detector signals a disturbance.