Direct digital frequency systhesizer
First Claim
1. A direct digital frequency synthesizer to output a sine signal, comprising:
- an accumulator sequentially outputting a sample address with a periodic MSB according to a frequency control signal, the sample address represented by N bits, wherein N is an integer;
a symmetry circuit controlled by a first clock with a period twice that of the MSB of the sample address to produce a symmetry sample address by producing a complement of the sample address;
a coarse circuit connected to the symmetry circuit to output a first M bits of the symmetry sample address as a first M bits of the sine signal, wherein M is an integer that is less than N;
a fine circuit connected to the symmetry circuit to predict a last N-M bits of the sine signal from a last N-M bits of the symmetry sample address according to the first M bits of the symmetry sample address; and
a sign circuit connected to the accumulator for receiving said sample address, the coarse circuit and the fine circuit, controlled by a second clock with a period four times that of the MSB of the symmetry sample address to output said sine signal and a sign bit of the sine signal.
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Accused Products
Abstract
A direct digital frequency synthesizer outputting a sine signal is disclosed, comprising an accumulator, a symmetry circuit, a coarse circuit, a fine circuit and a sign circuit, wherein the accumulator sequentially outputs a sample address according to a frequency control signal. The symmetry circuit takes the complement of the sample address according to a first clock, the period of the first clock being twice the period of the first MSB of the sample address, to obtain a symmetric sample address represented by N bits. The coarse circuit connected to the symmetry circuit outputs the first M MSBs of the symmetric sample address as the first M MSBs of the sine signal. The fine circuit predicts the last N-M LSBs of the sine signal from the last N-M LSBs of the symmetric sample address according to the first M MSBs of the symmetric sample address of the coarse circuit. Then, the sign circuit outputs a sign bit of the sine signal according to a second clock, the period of the second clock being four times that of the period of the first MSB of the symmetric sample address.
19 Citations
12 Claims
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1. A direct digital frequency synthesizer to output a sine signal, comprising:
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an accumulator sequentially outputting a sample address with a periodic MSB according to a frequency control signal, the sample address represented by N bits, wherein N is an integer; a symmetry circuit controlled by a first clock with a period twice that of the MSB of the sample address to produce a symmetry sample address by producing a complement of the sample address; a coarse circuit connected to the symmetry circuit to output a first M bits of the symmetry sample address as a first M bits of the sine signal, wherein M is an integer that is less than N; a fine circuit connected to the symmetry circuit to predict a last N-M bits of the sine signal from a last N-M bits of the symmetry sample address according to the first M bits of the symmetry sample address; and a sign circuit connected to the accumulator for receiving said sample address, the coarse circuit and the fine circuit, controlled by a second clock with a period four times that of the MSB of the symmetry sample address to output said sine signal and a sign bit of the sine signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of producing a sine signal by direct digital frequency synthesis comprising the steps of:
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sequentially generating a sample address with a periodic MSB according to a frequency control signal, the sample address being represented by N bits, wherein N is an integer; generating a symmetry sample address by producing a complement of the sample address; outputting a first M bits of the symmetry sample address as a first M bits of the sine signal, wherein M is an integer that is less than N; predicting a last N-M bits of the sine signal from a last N-M bits of the symmetry sample address according to the first M bits of the symmetry sample address in accordance with a linear approximation; and generating the sine signal based on the outputted M bits and the predicted N-M bits.
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Specification