Digital devices for spectrum analysis
AssigneeLe Materiel Telephonique
InventorJean P. Houdard
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Abstract
This invention relates to digital devices for spectral analysis. Signal x(t) of spectrum X(f), sampled at frequency 1/T and encoded, is processed by a temporal digital filter having a width NT followed by one or more perfect digital resonators in parallel, each tuned to a specific predetermined frequency f.sub.p and possessing two outputs, one being the "sine" output and the other being the "cosine" output on which the digital signals X(f.sub.p) sin 2.pi.f.sub.p kT and X(f.sub.p) cos 2.pi.f.sub.p kT are obtained after time NT, from which the value X.sup.2 (f.sub.p) can be formed by conventional digital processing. Application to encoded multifrequency signal receivers used in telephone switching.
Claims6
A digital device for analyzing the spectrum of a signal X(t), said signal having the spectral transform X(f), -Fe/2<f<Fe/2, and previously having been sampled at a frequency Fe=T, and linearly quantized and encoded to produce a digital series X* (nT), said device measuring the power spectral density of said signal and including:
- (a) a limiting gate of width .tau.=NT connected to the input of the device for processing the incoming signal X*(nT);
- (b) a perfect digital resonator, including first and second delay circuits each of delay T, connected to said limiting gate, said resonator having a first output S, known as the "sine" output and a second output "C" known as the "cosine" output;
- and
- (c) a read-only memory connected to said resonator, said memory storing q group of three coefficients, 2 cos 2.pi. fpT, and sin 2.pi. fpT, respectively, corresponding to the q frequencies of the analysis, characterized in that the device further comprises:
- (d) at least one read-write memory comprising a looped shift-register inserted between the output of said limiting gate and the input of said perfect resonator for storing N samples of said signal;
- and
- (e) means, connected to said first and second delay circuits in said perfect resonator, for resetting said delay circuits after the passage of the N samples stored in said read-write memory.
Dependencies are inferred from the claim text.