Frequency synthesizers having dividing ratio controlled by sigma-delta modulator
US4965531A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Nov 22, 1989 |
| Grant date | Oct 23, 1990 |
| Priority date | — |
| Expiry date | Nov 22, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03L7/1976
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
An indirect frequency synthesizer suitable for use in a cellular radio system has finer resolution and reduced spurious frequencies and/or phase noise, which facilitates a large number of channels in a given bandwidth. The synthesizer comprises a phase detector responsive to a reference signal and a phase control signal for generating a control signal that varies in dependence upon the phase difference between the reference signal and the phase control signal. A voltage controlled oscillator responsive to the control signal generates an output signal whose frequency varies in dependence upon the control signal. A variable modulus divider divides the output signal to provide the phase control signal. The variable modulus divider varies its division ratio in dependence upon a ratio control signal derived by a second or higher order sigma-delta modulator in response to a frequency control signal .delta..phi. and to the phase control signal. The sigma-delta modulator displaces any quantization noise in the ratio control signal away from the frequency of the phase control signal and multiplies thereof. A direct frequency synthesizer may be implemented by means of the same sigma-delta mo…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.