Tone decoder
US4197525A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 9, 1978 |
| Grant date | Apr 8, 1980 |
| Priority date | — |
| Expiry date | Nov 9, 1998 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04W88/027
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
An improved decoder for providing a decoder output signal when a tone signal contains frequencies that are sequentially within a predetermined passband surrounding first and second detection frequencies f.sub.1, f.sub.2. A tone signal is mixed with a reference signal which alternates, at a multiplex frequency, between sine and cosine signals, each being at a predetermined reference frequency which is less than the multiplex frequency. A tone switching logic circuit normally maintains the reference frequency at a value substantially equal to the frequency f.sub.1. The mixed signal is coupled through a demultiplexer to respective inputs of first, second, third and fourth low pass filters, each of which has a cut-off frequency which is one-half of the decoder passband. The respective outputs of the filters are coupled through a multiplexer to a squarer. Normally, the demultiplexer and the multiplexer are controlled by the tone switching logic ciruit so as to alternately couple, at the multiplex frequency, the mixed signal to the inputs of the first and second filters, and the outputs thereof to the squarer. The squarer output is applied to a summing amplifier, which removes the multip…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.