Enhanced quadrature notch filter
AssigneeHughes Aircraft Company
InventorPreben B. Jensen
Life of this patent
Estimating the term…
Abstract
An enhanced quadrature notch filter which is capable of rejecting an undesired signal component of an input signal, generally comprising a quadrature phase splitter for producing first and second reference signals which have substantially the same frequency as the undesired signal component but which are 90.degree. out of phase with each other, a pair of amplitude control loops for adding the first and second reference signals to the input signal in amplitudes which will cancel the undesired signal component, and a phase locked loop circuit for maintaining a predetermined phase relationship between the undesired signal component and one of the first and second reference signals.
Claims12
A method of rejecting an undesired frequency component of an input signal having an unknown phase, comprising the steps of:
- producing first and second reference signals having substantially the same frequency as said undesired frequency component but which are 90.degree. out of phase with each other;
- maintaining an approximately 45.degree. phase relationship between said undesired frequency component and one of said first and second reference signals;
- and
- adding said first and second reference signals to said input signal in amplitudes which will cancel said undesired frequency component.
A quadrature notch filter for rejecting an undesired frequency component of an input signal having an unknown phase, comprising:
- quadrature means producing first and second reference signals which have substantially the same frequency as said undesired frequency component but which are 90.degree. out of phase with each other;
- amplitude control loop means for adding said first and second reference signals to said input signal in amplitudes which will cancel said undesired frequency component;
- and
- phase locked loop means for maintaining a predetermined phase relationship between said undesired frequency component and one of said first and second reference signals, said phase lock loop means including hybrid means for providing an approximately 45.degree. phase relationship between said undesired frequency component and one of said reference signals.
A quadrature notch filter for rejecting an undesired frequency component of an input signal, comprising:
- an oscillator which generates an output signal that has substantially the same frequency as said undesired frequency component;
- a quadrature hybrid circuit which splits said output signal into first and second reference signals, said first and second reference signals being 90.degree. out of phase with each other;
- an amplitude control loop circuit for each of said first and second reference signals which adds said first and second reference signals to said input signal in amplitudes which will cancel said undesired frequency component;
- a hybrid circuit which produces a third reference signal having a phase which is between the phases of said first and second reference signals;
- a phase detector circuit which compares the phase of said undesired frequency component with the phase of said third reference signal and produces a feedback signal that is related to the compared phase difference;
- and
- an integrator circuit which controls said oscillator such that said oscillator will maintain a predetermined phase relationship between said undesired frequency component and said third reference signal.
Dependencies are inferred from the claim text.