engleski

Sigma-delta look-up table based Gaussian shaper

Gaussian filters are commonly used for pulse shaping of rectangular data signals. Modulation of a high-frequency carrier by such shaped signals gives the Gaussian Minimum Shift Modulation (GMSK) scheme. As a result of the pulse shaping, GMSK has a narrower power spectrum than MSK signal, and especially narrower than base-band data signal. There are many different approaches for realization of Gaussian filter ; from analog multistage RC- or SC-filters, to different digital filters. Of particular interest are solutions with look-up-table (LUT). LUT saves the basic elements of already Gaussian-shaped signal elements, and is basically realized by PCM sampling of Gaussian-shaped signal. PCM based LUTs are hardware consuming and at output they need n-bit D/A converter. Our proposition is the use of 1-bit Sigma Delta Modulation (SDM) for sampling of a Gaussian-shaped signal. The results are smaller ROM capacity, 1-bit wide output word, and 1-bit D/A converter realized as a simple first order low-pass RC filter. This article describes simple, but efficient SDM LUT-based Gaussian shaper that can be used for generation of GMSK and GFSK modulated signals. Measured oscillograms and power spectrums are obtained for 10-bit pseudo-noise sequence input signal for SDM LUT based Gaussian shaper realized in FLEX AlteraTM PLD.

Gaussian filter; Minimum Shift Keying; look-up table

nije evidentirano