DTMF receiver
US4833399A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 13, 1988 |
| Grant date | May 23, 1989 |
| Priority date | — |
| Expiry date | Jun 13, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R23/14
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A DTMF receiver (10) recognizes each of a plurality of multi-frequency tones, each tone centered on a predetermined standard frequency. Two digital bandpass filters (14, 16) each have four frequency bins, each frequency bin operating according to a recursive second-order transfer function for preferentially transmitting frequencies near the standard frequencies. Each frequency bin accumulates, for each of a plurality of sampling periods, respective spectral energy signals from the input signal. A temporal energy signal is derived from the spectral energy signals. For each bandpass filter (14, 16), a time-domain test template generator (30) and a frequency-domain test template generator (34) are provided to generate time-domain and frequency-domain test templates. These test templates are input to an analyzer (38) that compares the templates against data-adaptive frequency-domain and time-domain reference templates.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.