Method and apparatus for generating digital dual frequency signals
US3985966A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 23, 1975 |
| Grant date | Oct 12, 1976 |
| Priority date | — |
| Expiry date | Jul 23, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04Q1/4575
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A dual tone multiple frequency digital tone generator for a PCM/TDM electronic telephone system. A digital representation of a dual tone signal is generated from a multi-bit command character by determining the phase angle of two frequencies specified by the command character relative to an independent time reference signal, converting paired phase angles to amplitude signals representative of the amplitude of a sine wave having each calculated phase angle, and summing the amplitude representations to generate a value corresponding to the digital representation of the frequency pair at that particular instant. Individual phase angles are calculated by generating a multi-bit digital character corresponding to the phase angle of a sinusoidal reference signal of the particular frequency. This character is preferably generated by multiplying a multi-bit digital character having n-bits representing the fractional part of the number of seconds elapsed from some reference time by a multi-bit digital character having m bits representing the frequency of the sinusoidal signal, m and n both integers. The resulting m + n bit product consisting of an m-bit integral part and an n-bit fractional…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.