Table of Contents
International Journal of Microwave Science and Technology
Volume 2015, Article ID 757591, 7 pages
Research Article

Implementation of a Cross-Spectrum FFT Analyzer for a Phase-Noise Test System in a Low-Cost FPGA

1Institute for Communication Systems ICOM, University of Applied Sciences of Eastern Switzerland, 8640 Rapperswil, Switzerland
2Anapico Ltd., 8152 Glattbrugg, Switzerland

Received 1 June 2015; Revised 1 September 2015; Accepted 2 September 2015

Academic Editor: Giovanni Ghione

Copyright © 2015 Patrick Fleischmann et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The cross-correlation method allows phase-noise measurements of high-quality devices with very low noise levels, using reference sources with higher noise levels than the device under test. To implement this method, a phase-noise analyzer needs to compute the cross-spectral density, that is, the Fourier transform of the cross-correlation, of two time series over a wide frequency range, from fractions of Hz to tens of MHz. Furthermore, the analyzer requires a high dynamic range to accommodate the phase noise of high-quality oscillators that may fall off by more than 100 dB from close-in noise to the noise floor at large frequency offsets. This paper describes the efficient implementation of a cross-spectrum analyzer in a low-cost FPGA, as part of a modern phase-noise analyzer with very fast measurement time.