US Patent 7519193 Hearing aid circuit reducing feedback

A hearing aid circuit includes a correlation detector that detects correlation at a feedforward path input and that provides a correlation output to a phase shifter. The phase shifter introduces a phase shift along a feedforward path. A phase measurement circuit measures a phase shift at a feedforward path input, and provides a phase measurement output to an internal feedback processor. The internal feedback processor adjusts internal feedback as a function of the phase measurement to suppress coupling of external audio feedback along the feedforward path.