Source: http://www.google.de/patents/US5305309
Timestamp: 2013-12-06 05:14:39
Document Index: 554181170

Matched Legal Cases: ['arts 61', 'art 61', 'art 62', 'art 62', 'art 61', 'arts 61', 'arts 71', 'art 71', 'art 72', 'art 120', 'art 114', 'art 121', 'art 115', 'art 120', 'art 121']

Patent US5305309 - Echo canceller - Google PatenteSuche Bilder Maps Play YouTube News Gmail Drive Mehr » Erweiterte Patentsuche | Anmelden Erweiterte Patentsuche PatenteAn echo cancellor includes an echo replica generator which generates an echo replica signal based on a received signal, a subtractor which obtains a transmitting side output signal by subtracting the echo replica signal from a transmitting side input signal, a divergence detector which detects a divergence...http://www.google.de/patents/US5305309?utm_source=gb-gplus-sharePatent US5305309 - Echo canceller Ver�ffentlichungsnummerUS5305309 APublikationstypErteilung AnmeldenummerUS 07/974,664 Ver�ffentlichungsdatum19. Apr. 1994Eingetragen12. Nov. 1992 Priorit�tsdatum6. Dez. 1989Geb�hrenstatusVerfallen Ver�ffentlichungsnummer07974664, 974664, US 5305309 A, US 5305309A, US-A-5305309, US5305309 A, US5305309A ErfinderKaoru Chujo, Masako KatohUrspr�nglich Bevollm�chtigterFujitsu LimitedPatentzitate (8), Referenziert von (35), Klassifizierungen (5), Juristische Ereignisse (3) Externe Links: USPTO, USPTO-Zuordnung, EspacenetEcho cancellerUS 5305309 A Zusammenfassung An echo cancellor includes an echo replica generator which generates an echo replica signal based on a received signal, a subtractor which obtains a transmitting side output signal by subtracting the echo replica signal from a transmitting side input signal, a divergence detector which detects a divergence of the echo cancellor based on the transmitting side input signal and the echo replica signal and outputs a detection signal when the divergence is detected, and a resetting part which automatically resets the echo replica generator in response to the detection signal from the divergence detector.
What is claimed is: 1. An echo canceller comprising:echo replica generating means for generating an echo replica signal based on a received signal and including filter having tap coefficients; subtracting means coupled to said echo replica generating means for obtaining a transmitting side output signal by subtracting the echo replica signal generated by said echo replica generating means from a transmitting side input signal; divergence detecting means coupled to said echo replica generating means and said subtracting means for detecting a divergence of the echo canceller based on the transmitting side input signal and the echo replica signal, the detecting being based on a comparison between a first power of the transmitting side input signal and a second power of the echo replica signal and for outputting a detection signal when the divergence is detected; and resetting means coupled to said divergence detecting means for automatically resetting said echo replica generating means in response to the detection signal from said divergence detecting means. 2. The echo canceller as claimed in claim 1, wherein said filter in said echo replica generating means comprises an adaptive filter including a storage for storing the received signal as tap values, and for storing tap coefficients corresponding to the tap values, an echo replica generator for generating the echo replica signal based on the tap values and the tap coefficients corresponding to the tap values, and a tap coefficient updating circuit for updating the tap coefficients based on the received signal and the transmitting side output signal so that the tap coefficients converge, said divergence of the echo canceller being a divergence of the tap coefficients of said adaptive filter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of the operating principle of an echo canceller according to the present invention, by referring to FIGS. 4 through 7.
FIG. 9 shows an embodiment of the divergence detector 6. The divergence detector 6 includes signal power calculating parts 61 and 62, a coefficient multiplier 63, and a comparator 64 which are coupled as shown. The signal power calculating part 61 calculates a signal power P.sub.er of the echo replica signal, and the signal power calculating part 62 calculates a signal power P.sub.si of the transmitting side input signal. The coefficient multiplier 63 multiplies a predetermined coefficient K to the transmitting side input signal power P.sub.si which is calculated in the signal power calculating part 62. The predetermined coefficient K is slightly larger than 1. The comparator 64 compares the echo replica signal power P.sub.er which is calculated in the signal power calculating part 61 and the signal power K multiplier 63, and outputs a detection signal which indicates whether or not the divergence has occurred depending on the result of the comparison.
The divergence detector 6 detects the existence of the above described divergence. The echo replica signal power P.sub.er and the transmitting side input signal power P.sub.si are respectively calculated in the signal power calculating parts 61 and 62, and the coefficient multiplier 63 multiplies the coefficient K to the transmitting side input signal power P.sub.si by taking into account a certain margin. When P.sub.si comparator 64, no divergence has occurred. On the other hand, a divergence has occurred when P.sub.si comparison in the comparator 64.
The signal power calculating parts 71 and 72 respectively calculate the signal powers of the transmitting side input signal and the transmitting side output signal. The coefficient multiplier 73 multiplies a predetermined coefficient K to a transmitting side input signal power P.sub.si which is output from the signal power calculating part 71. The predetermined coefficient K is slightly larger than 1. The comparator 74 compares a signal power K signal power P.sub.so which is output from the signal power calculating part 72. The comparator 75 compares the transmitting side output signal power P.sub.so and a predetermined threshold value TH of the transmitting side output signal power P.sub.so. The AND circuit 76 outputs a detection signal based on output signals of the comparators 74 and 75.
In other words, the divergence detector 7 detects the divergence when P.sub.so &gt;TH and P.sub.si detected, the divergence detector 7 supplies the detection signal to the tap value storage 1 and the tap coefficient storage 3.
R=E[XY]
X =X.sub.n �X.sub.n-M
Y =Y.sub.n �Y.sub.n-M
E[XY]=(1/M)ΣX.sub.n-i Y.sub.n-i
E[X.sup.2 ]=(1/M)ΣX.sub.n-i
E[Y.sup.2 ]=(1/M)ΣY.sub.n-i.
The correlation judging part 120 compares the correlation function R from the correlation calculating part 114 and a correlation function threshold value Th.sub.R and outputs a signal "1" when R &lt;Th.sub.R. The signal power judging part 121 compares the signal power P from the signal power calculating part 115 and a signal power threshold value Th.sub.P and outputs a signal "1" when P &gt;Th.sub.P. The AND circuit 122 outputs a signal "1" as the detection signal in response to the output signals of the correlation judging part 120 and the signal power judging part 121.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining the echo phenomenon;
BACKGROUND OF THE INVENTION The present invention generally relates to echo cancellers, and more particularly to an echo canceller which is used in a long-distance telephone system, a telephone conference system, a video telephone conference system and the like.
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