Abstract: An apparatus and method for detecting the presence of ringer signals in a telephone which samples the incoming telephone signals within a prescribed time interval, windows the signals, and computes a set of auto-correlation coefficients. These coefficients are normalized, and their absolute values are calculated and summed and compared with an empirically-derived threshold. If the coefficient sum exceeds the threshold, a high degree of correlation within incoming signals is indicated, distinguishing the incoming signal as containing ringer signal constituents.

Abstract: A method is disclosed for maintaining loop stability between a transmit and a receive path of a speaker phone which is capable of operating in either a full-duplex or a half-duplex mode. Loop stability is maintained and normal operation is achieved by controlling transmit and receive path attenuators. The method first determines whether feedforward or feedback signal levels should be used. Based on this determination, the signal and noise parameters along various points in the transmit and receive path are evaluated. Based on the parameter values, the transmit and receive attenuators are adjusted to maintain loop stability and to operate the speaker phone in the proper state. Additionally, when the speaker phone adjusts the transmit attenuator for greater signal attenuation in order to maintain loop stability the noise fill-in component of the speaker phone will generate additional background noise to maintain a constant background noise level, as perceived by the far-end user.