Patent ID: 7555117

Claim:
In a telephone including an audio frequency circuit having a first channel, a second channel, and at least one echo canceling circuit coupled between said first channel and said second channel, the improvement comprising: a summation circuit having an input and an output in said first channel; a path change detector coupled to said input and to said output, said path change detector producing a first output signal when said echo canceling circuit diverges and producing a second output signal otherwise; wherein said path change detector includes: a programmable gain amplifier having an input coupled to the output of said summation circuit and an output; a comparator having a first input coupled to the output of said programmable gain amplifier and a second input coupled to the input of said summation circuit, whereby said path change detector, in effect, determines whether or not the quotient of the magnitude of a signal on the output of the summation circuit divided by the magnitude of a signal on the input of the summation circuit exceeds a threshold.