Digital multitone generator for telephone dialing
US4058805A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 16, 1975 |
| Grant date | Nov 15, 1977 |
| Priority date | — |
| Expiry date | Jun 16, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/505
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A digital signal generator that produces multifrequency tones in the voice band range for use in telephone station sets utilizing multitone dialing. Amplitude information describing each of eight voice band frequencies is digitally encoded into a sequence of multi-bit words describing the amplitude at successive data points along the waveform. The eight frequencies so encoded are separated into four upper and four lower frequencies and stored in two solid state read-only memories. Upon command amplitude data words for one upper and one lower frequency are sequentially read out of the memory in time synchronization, added, and their sum applied to a digital delta modulation circuit. The delta modulator determines the change between two successive data word sums and describes the change by an output of either a binary one or a binary zero. The delta modulator output thus comprises a series of binary ones and/or zeros forming an aperiodic digital pulse train which is applied to an output module consisting of an integrating network to synthesize an approximation of a multitone dialing waveform which is compatible with the common carrier telephone network.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.