Patent ID: 6911863

Claim:
A filter for processing frequency signals, comprising a Chebyshev filter ( 11 , 12 ), a subsequent all-pass filter ( 13 ) producing an output signal and a control device ( 14 to 20 ) comprising a frequency synthesizer ( 14 ) producing a controllable reference frequency for controlling the Chebyshev filter ( 11 , 12 ) and the all-pass filter ( 13 ), wherein the frequency synthesizer ( 14 ) generates a reference signal at a reference frequency (fref), and the control device further comprises a reference low-pass filter ( 16 ) which shifts the phase of the reference signal by 90 degrees, and a phase detector ( 18 ) which compares the phase positions of the reference signal and the output signal of the reference low-pass filter ( 16 ) and generates an output signal for controlling the frequency position of the Chebyshev filter ( 11 , 12 ), the all-pass filter ( 13 ) and the reference low-pass filter ( 16 ).