Lattice Phase Equaliser - Unbalanced Topology

Unbalanced Topology

The lattice phase equaliser cannot be directly transformed into T-section topology without introducing active components. However, a T-section is possible if ideal transformers are introduced. Transformer action can be conveniently achieved in the low-in-phase T-section by winding both inductors on a common core. The response of this section is identical to the original lattice, however, the input is no longer constant resistance. This circuit was first used by George Washington Pierce who needed a delay line as part of the improved sonar he developed between the world wars. Pierce used a cascade of these sections to provide the required delay. The circuit can be considered a low-pass m-derived filter with m>1 which puts the transmission zero on the jω axis of the complex frequency plane. Other unbalanced transformations utilising ideal transformers are possible, one such is shown on the right.