Filter and demodulation circuit for filtering an intermediate frequency modulated signal carrying a modulation signal
US4903332A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 2, 1988 |
| Grant date | Feb 20, 1990 |
| Priority date | — |
| Expiry date | Mar 2, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03D3/005
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
Intermediate frequency signals are produced by mixing with an oscillator voltage and subsequently filtered and demodulated. The oscillator voltage or the resonance frequency of the filter or filters are followed up by a control voltage derived from the demodulated signal corresponding to the intermediate frequency. The perturbatory phase modulator occurring as a result of the control lag is compensated by opposite-phase phase-modulation which is superimposed on the intermediate frequency. In this, the phase modulation is achieved by a phase modulator which is connected with the output of a demodulator by a matching circuit. Another possibility for achieving phase modulation of the intermeidate frequency is to modulate the oscillator of the mixing stage.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.