Signal quality
First Claim
1. A method for improving the quality of the output signal of an audio output stage, which comprises at least a modulator circuit (301), characterized in thata signal generated in the audio output stage, which signal is proportional to a previous digital input signal, is compared by means of feedback to the digital input signal (IN) of the audio output stage in order to generate a digital control signal (307) and wherein the feedback takes place at a higher rate than the digital input signal, and the operation of said modulator circuit (301) is controlled by means of said digital control signal (307).
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Accused Products
Abstract
The invention relates to a method for improving the quality of the output signal of especially an audio output stage, which comprises at least a modulator circuit, in such a manner that in accordance with the method a signal generated in the output stage, which signal is proportional to a previous digital input signal, is compared by means of feedback to the digital input signal (IN) of the output stage in order to generate a digital control signal (307), and the operation of said modulator circuit (301) is controlled by means of said digital control signal (307). The invention further relates to an audio output stage which comprises a modulator circuit (301) to modulate a digital input signal (IN), amplifier circuit (302) to amplify a modulated signal, and a filter circuit (303) to filter a modulated and amplified signal, and which audio output stage further comprises a m comparator circuit (305) for comparing the digital input signal (IN) and a signal generated in the output stage, which signal is proportional to a previous digital input signal, and for generating a digital control signal (307) for the modulator circuit (301).
39 Citations
28 Claims
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1. A method for improving the quality of the output signal of an audio output stage, which comprises at least a modulator circuit (301), characterized in that
a signal generated in the audio output stage, which signal is proportional to a previous digital input signal, is compared by means of feedback to the digital input signal (IN) of the audio output stage in order to generate a digital control signal (307) and wherein the feedback takes place at a higher rate than the digital input signal, and the operation of said modulator circuit (301) is controlled by means of said digital control signal (307).
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7. A method for improving the quality of the output signal of an audio output stage, which comprises at least a modulator circuit (301), wherein:
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a signal generated in the audio output stage, which signal is proportional to a previous digital input signal, is compared by means of feedback to the digital input signal (IN) of the audio output stage in order to generate a digital control signal (307), the operation of said modulator circuit (301) is controlled by means of said digital control signal (307), a digital input signal brought to the output stage is converted into a pulse train by means of modulation, said pulse train is amplified, said pulse train is filtered in the feedback circuit to a frequency range corresponding to the input signal, the filtered pulse train is converted into a digital signal in the feedback circuit, bits are added to said digital signal so that it corresponds to the input digital word as regards the number of bits, said input digital word and said digital signal are compared so as to produce a difference signal, change data for the digital difference signal are determined, and on the basis of said change data the conversion of the input digital word of the output stage into a pulse train is controlled by means of the digital control signal (307). - View Dependent Claims (9, 10, 25)
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8. A method for improving the quality of the output signal of an audio output stage, which comprises at least a modulator circuit (301), wherein:
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a signal generated in the audio output stage, which signal is proportional to a previous digital input signal, is compared by means of feedback to the digital input signal (IN) of the audio output stage in order to generate a digital control signal (307), the operation of said modulator circuit (301) is controlled by means of said digital control signal (307), a digital input word brought to the output stage is converted into a pulse train by means of modulation, said pulse train is amplified, said pulse train is filtered so as to make it suitable for output means, said pulse train filtered suitable for the output means is filtered in the feedback circuit to a frequency range corresponding to the input signal, the filtered pulse train is converted into a digital signal in the feedback circuit, bits are added to said digital signal so that it corresponds to the input digital word as regards the number of bits, said input digital word and said digital signal are compared so as to produce a difference signal, change data for the digital difference signal are determined, and on the basis of said change data the conversion of the input digital word of the output stage into a pulse train is controlled by means of the digital control signal (307). - View Dependent Claims (26)
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11. An audio output stage for improving the quality of an output signal, which audio output stage comprises
a modulator circuit (301) for modulating a digital input signal (IN), an amplifier circuit (302) for amplifying the modulated signal, a filter circuit (303) for filtering the modulated and amplified signal, characterized in that the audio output stage further comprises a comparator circuit (305) for comparing the digital input signal (IN) and a signal generated in the output stage, which signal is proportional to a previous digital input signal, and for generating a digital control signal (307) for the modulator circuit (301) wherein the signal generated in the output stage updated at a higher rate than the digital input signal.
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17. An audio output stage for improving the quality of an output signal, which audio output stage comprises
a modulator circuit (301) for modulating a digital input signal (IN), an amplifier circuit (302) for amplifying the modulated signal, a filter circuit (303) for filtering the modulated and amplified signal, characterized in that the audio output stage further comprises a comparator circuit (305) for comparing the digital input signal (IN) and a signal generated in the output stage, which signal is proportional to a previous digital input signal, and for generating a digital control signal (307) for the modulator circuit (301) wherein said comparator circuit (305) comprises, a means (314) to filter a feedback signal, a means (308) to A/D convert the filtered feedback signal (304), a means (309) to add bits in the A/D-converted feedback signal, a means (310) to synchronize the A/D-converted and bit-added feedback signal with the input signal (IN), a means (311) to compare the A/D-converted, bit-added and synchronized feedback signal to the input signal (IN) in order to produce a difference signal, a means (312) to process said difference signal, and a means (313) to convert said difference signal into a suitable control signal (307) on the basis of the result of the difference signal processing.
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18. A mobile station comprising an audio output stage (612) for processing a received audio signal, characterized in that the audio output stage (612) of the mobile station comprises
a first means (613) to modulate a digital signal, a second means (614) to amplify a modulated signal, a third means (615) to filter a modulated and amplified signal, a fourth means (616) to generate a digital control signal (307) by comparing the input signal (IN) to a signal generated in the output stage the signal generated in the output stage being updated at a rate higher than the input signal, which signal generated in the output stage is proportional to a previous digital input signal, and by processing the signal which is the result of the comparison in such a manner that it becomes a digital control signal suitable for the first means (613).
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20. A method for improving a quality of an output signal of an audio output stage which comprises at least a modulator circuit, the method comprising:
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comparing a signal generated in the audio output stage, which signal is proportional to a previous digital input signal, by means of feedback to the digital input signal of the audio output stage, in order to generate a digital control signal;
converting a digital output signal brought to the audio output stage into a pulse train by means of modulation;
controlling an operation of the modulator circuit by means of the digital control signal, wherein the method further comprises;
amplifying the pulse train;
filtering the pulse train in the feedback circuit to a frequency range corresponding to the input signal;
converting the filtered pulse train into a digital signal in the feedback circuit, adding bits to the digital signal so that the digital signal corresponds to the input digital word as regards the number of bits;
comparing the input digital word and the digital signal so as to produce a difference signal;
determining a change data for the digital difference signal; and
on the basis of the change data the conversion of the input digital word of the output stage into a pulse train is controlled by means of a digital control signal. - View Dependent Claims (21, 22, 28)
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23. A method for improving a quality of an output signal of an audio output stage which comprises at least a modulator circuit, the method comprising:
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comparing, by means of feedback to a digital input signal of the audio output stage, a signal generated in the audio output stage, which signal is proportional to a previous digital input signal, the feedback taking place at a higher rate than the digital input signal;
generating a digital control signal based on the comparison; and
controlling an operation of the modulator circuit by means of the digital control signal, wherein at least one reference level in the modulator circuit is changed by use of the digital control signal. - View Dependent Claims (24)
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Specification