Telephone answering device with low cost dual tone multi-frequency detector
US5699421A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 31, 1995 |
| Grant date | Dec 16, 1997 |
| Priority date | — |
| Expiry date | May 31, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04Q1/453
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A telephone answering device (TAD) includes a remote access mode which is operative responsive to dual tone multi-frequency (DTMF) signals. At least three bandpass filters each receive an input signal from a telephone line interface provided in the TAD. A software controlled sampling section receives outputs from all the bandpass filters for sampling outputs from the bandpass filters, the sampling section including a multiplexer which receives the outputs from all of the bandpass filters, and a peak hold circuit coupled to an output of the multiplexer. An analog-to-digital converter receives an output from the peak hold circuit, and a digital controller receives the output of the analog-to-digital converter for controlling operations of the TAD in a remote access mode responsive to the detected DTMF signals. First and second ones of the bandpass filters have respective center frequencies corresponding to frequencies of respective DTMF signals and a third bandpass filter has a different center frequency. The absence of an output from the third filter confirms that there is no noise or other undesirable signals that would indicate that an incoming signal is not a DTMF signal. At leas…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.