US 6,476,685 B1Granted

Network for providing group delay equalization for filter networks

OwnerWilliam S. H. Cheunginventor

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Abstract

A circuit and method for creating an all pass network for equalizing the group delay of a filter. The all pass filter provides an equalization network including a transformer having a primary and secondary winding magnetically coupled together. One end of each primary and secondary winding is connected together to form a connection, the remaining ends of the primary and secondary winding constitute input and output terminals to the equalization network. Control over the group delay response is effected by a bias conductor serially connected to the common ends of the primary and secondary winding and a capacitor connected to the common terminal. The bias conductor modifies the mutual inductance, therefore modifying the coupling factor for the transformer. By shifting control of the coupling to the bias conductor, group delay response may be controlled without further modifications of the transformer coupling.

Claims8

Dependent claims

An equalization network for compensating a non-linear group delay function comprising:

a transformer having a primary winding and a secondary winding magnetically coupled together said primary and secondary windings having respective inductance of Lp and Ls, and a theoretical coupling factor K controlling the mutual inductance between said primary and secondary windings, and a measured coupling factor Ko;
a first capacitance connected between first ends of said primary and secondary windings, forming and input terminal with said primary winding and an output terminal with said secondary winding;
a bias inductor connected to second ends of said primary and secondary windings having an inductance which is determined by:
Lb={[2*Ko*Lp*(1+K)]/[2*(1+Ko)]}−(K*Lp)
where Lp is the calculated winding inductance;
K is the calculated coupling factor for the transformer;
Ko is the measured coupling factor of the transformer;
and
a capacitor connecting a second end of said bias inductor to a common terminal, said inductor modifying said transformer coupling between said primary and secondary windings to obtain substantially a coupling factor of K, and said primary and secondary windings inductances Lp, Ls are modified to obtain a desired group delay response of a second order all pass network having a circuit pole -zero Q less than one based on said theoretical and actual coupling factors K and Ko whereby the phase delay through said network may be accurately controlled.

6 more elements

Dependencies are inferred from the claim text.