Method of determining levels at given frequencies of a VF signal
Patent 5353344 Issued on October 4, 1994. Estimated Expiration Date: 
September 18, 2012. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
September 18, 2012. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3875347 Dual tone multifrequency and dial pulse receiver Digital DTMF tone detector Configurable parameter DTMF detector Multi-frequency signal receiver and a method of detecting the multi-frequency signal Patent #: 5214693 InventorAssigneeApplicationNo. 947069 filed on 09/18/1992US Classes:379/386, Signal receiver (e.g., tone decoder)379/283, Dual tone multifrequency (DTMF) receiver708/312Tone detectionExaminersPrimary: Dwyer, James L.Assistant: Weaver, Scott L. Attorney, Agent or FirmForeign Patent References
International ClassesG06F 015/31H04M 003/00 Foreign Application Priority Data1991-09-24 CHAbstractA dialing receiver (1) for determining multifrequency dialing signals on an incoming signal in a telecommunication switching system, including a sampling circuit (4) for taking N values of the incoming signal at a given sampling rate, where N is a positive integer; a zero value generator circuit (6) for supplementing at the given sampling rate the N samples with M successive zero values so as to yield N+M values, where M is a positive integer; a discrete Fourier transformation circuit (7) for performing a discrete Fourier transform (DFT) of said N+M values in accordance with the Goertzel algorithm; and a result evaluating circuit (8) for directly evaluating the results of the DFT processing of the N+M values without interpolation so as to determine the identity of the multifrequency dialing signals.Other References
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