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| Home > Publications database > Digitale Synthese schmalbandiger Rauschsignale mit numerisch gesteuerten Oszillatoren |
| Home > Publications database > Digitale Synthese schmalbandiger Rauschsignale mit numerisch gesteuerten Oszillatoren |
| Book/Report | FZJ-2019-00815 |
1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21407
Report No.: Juel-3137
Abstract: In general, noise is regarded as undesired disturbance. In contrast to this, narrowband rf-noise signals with specific statistical properties are increasingly used for various applications in communications, RADAR and measurement techniques. In other scientific fields, like accelerator physics, noise of controlled spectral form is required for various applications. Therefore, for a number of applications narrowband rf-noise signals with an arbitrarily selectable, precisely tailored, and sharply delimited power density spectrum and defined statistical properties are useful or required. For generating such narrowband rf-noise signals, analog components are normally used, namely broadband noise sources, sine and sweep generators and tuneable high quality quartz filters. Perfection of digital integrated circuits inthe last 20 years made it possible to introduce new techniques into frequency generation, namely Direct Digital Frequency Synthesis (DDFS). DDFS based on Numerically Controlled Oscillators (NCO's) offer many advantages over traditional frequency generation schemes due to their wide frequency range, excellent output phase noise, wideband tuning linearity, and fast, phase-continuous frequency switching, which can not be achieved by using analog techniques. In the present dissertation we shall discuss the use of DDFS based on NCO's for generating narrowband rf-noise signals with an arbitrarily selectable power density spectrum and a carrier sweep in real time. The principal idea is based on the fact that any bandpass random process can be expressed in the Quadrature Amplitude Modulation (QAM) form. From this point of view we design a new QAM architecture with two phase modulated NCO's and without a multiplier, which allowes a higher dock rate compared to the c1assical QAM. Further, starting from discrete narrowband harmonic random process, we derive a suitable synthesis algorithm for the calculation of the envelope magnitude and phase function of the desired equivalent random baseband process. For investigating the statistical properties of thegenerated rf-noise signals, we first quantify the spurious signals generated by the phase modulation of an NCO. Based on those, we present an closed form solution of the statistical properties corrupted by quantization effects and spurious signals of the NCO's. A system prototype of the digital rf-noise generator has been designed and built, and several tests have been performed in order to demonstrate proper operation. Measurements of the statistical properties of the generated narrowband rf-noise signals are shown to be in good agreement with both theoretical and simulation results.
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