Direct digital synthesis frequency-agile QPSK modulator
US5784413A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 6, 1996 |
| Grant date | Jul 21, 1998 |
| Priority date | — |
| Expiry date | Sep 6, 2016 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/2092
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A frequency-agile, direct digital synthesis (DDS) modulator includes a double conversion architecture which provides an output signal having a good output spectrum with low spurious signals. The modulator is particularly suitable for providing a quadrature phase-shift keyed (QPSK) data signal. The modulator includes a direct digital synthesizer (DDS) for generating a data signal in response to a clock signal operating at an associated clock frequency. Two local oscillators are provided for respectively up-converting and then down-converting the DDS data signal to provide the output signal having the desired spectral characteristics. The first local oscillator operates at a first mixing frequency, while the second local oscillator is responsive to the clock signal for providing a second mixing signal at the clock frequency. This configuration eliminates the need for a phase lock loop for the second oscillator. Additionally, a digital-to-analog converter which is coupled to the DDS operates according to the clock signal. The first mixing frequency and the clock frequency are fixed, so that the frequency agility of the modulator is provided via an adjustable data signal which is outpu…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.