Back to results
US 4,540,855 AGranted
Detecting signals within a passband on a telephone line
AssigneeMelita Electronic Labs, Inc.
InventorsAleksander Szlam, Chester P. Quinn
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneeMelita Electronic Labs, Inc.
InventorsAleksander Szlam, Chester P. Quinn
Estimating the term…
An improved combination of a hardware and digital signal processing filter for detecting pick-up of a telephone call, solely through audio information on the telephone line. The apparatus employs a high gain band pass filter (28) with no automatic gain control, the output of which goes to a window comparator (30). The output from the window comparator (31) goes to a digital high pass filter (32) and from there to an integrator 37 for providing a digital output signal (40) indicative of the presence or absence on the telephone line of a signal exceeding a predetermined magnitude within the filter pass band. The digital signal is then processed by an intelligent digital filter having a set of predetermined threshold values of durations for states of the digital output signal, by which determinations of pick-up are made. The digital filter is adaptive and learns the durations high and low states of the digital output signal as they occur, subsequently checking for deviations from previously learned valid values. The digital filter includes a digital phase lock loop which will lock into a periodic but asymmetric pattern in the digital output signal and declare pick-up when lock is lost.
Apparatus for providing a digital output signal characterized by being in a first state or a second state, in response to signals on a telephone line comprising in combination:
Apparatus as recited in claim 4, wherein said integrating filter means includes a retriggerable monostable multivibrator, including a triggering input connected to receive said comparator output signal and a characteristic one-shot timing period less than or equal to the reciprocal of a lowest frequency of interest present in said signal on said telephone line.
Apparatus for providing a digital output signal characterized by being in a first state or a second state, in response to signals on a telephone line comprising in combination;
Dependencies are inferred from the claim text.