Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synthesizer
Reexamination Certificate
1999-06-24
2001-07-17
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synthesizer
C327S105000, C708S271000
Reexamination Certificate
active
06262604
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a digital synthesizer of signals. It can be applied especially to direct digital frequency synthesis, for example in the field of radar technology or in that of instrumentation.
Direct digital synthesis is a technique of frequency synthesis by which the samples of a signal to be generated are prepared in tile form of digital values and then converted into analog signal form by means of a digital-analog converter. The signal synthesizers obtained by this technique are highly valuable in terms of volume, weight and energy consumption because they enjoy the advantage of large-scale integration. Their other particular advantages are very high resolution and very short times of switching from one frequency to another.
In general, the digital-analog converter has a resolution of less than the number N of useful digital bits of the signal that is prepared for conversion into an analog signal. The passage from N bits to M bits, which is the resolution of the digital-analog converter, generates a quantification error. Owing to this quantification, the transfer function of the digital-analog converter, namely the output voltage from the converter as a function of the input digital words, is a stepped function.
In these digital synthesizers, the spectral purity is furthermore limited by the non-linearities of the digital-analog converters that they contain. The non-linearities designate the fact that the steps of the transfer function of the digital-analog converter are not of equal height and that the transition between steps produces irregular phenomena. These non-linearities lead to the generation of harmonic frequencies that are aliased owing to the sampling. Parasitic lines are thus created, a parasitic line being a spectral component located at frequencies different from the fundamental frequency of the signal to be synthesized.
SUMMARY OF THE INVENTION
One aim of the invention is to enable an improvement in the spectral purity of the digital synthesizers of signals by reducing the effect of the non-linearities of the digital-analog converters that they contain. To this end, an object of the invention is a signal synthesizer comprising means for the generation of the samples of a digital signal to be converted, encoded on N bits, into an analog signal as a function of a frequency control word, means for the generation of a noise signal encoded on N bits, the useful signal and the noise signal being added up by an adder, M most significant bits of the result of the addition being converted into analog signals by the digital-analog converter, M being smaller than N, the means for the generation of a noise signal comprising at least means for the generation of a sampled and equiprobable white noise, means for interposing a zero between two noise samples and means for the symmetrical pulsed response filtering of the samples with an offset of one sampling half-period so that the noise has at least a noise density substantially equal to the law of equiprobability, this density being zero outside a given space, and the histogram of the noise being stationary.
REFERENCES:
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patent: 5459680 (1995-10-01), Zimmerman et al.
patent: 5729182 (1998-03-01), Fousset et al.
patent: 0 887 941 A1 (1998-12-01), None
patent: WO 89/06009 (1989-06-01), None
de Gouy Jean-Luc
Gabet Pascal
"Thomson-CSF"
Le Dinh T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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