Method and apparatus for direct digital frequency synthesizer

Details Method and apparatus for direct digital frequency synthesizer Method and apparatus for direct digital frequency synthesizer

1995-08-30

1998-04-07

Malzahn, David H.

Boots, shoes, and leggings

G06F 102

Patent

active

057372535

ABSTRACT:
The present invention comprises a direct digital frequency synthesizer. A phase accumulator provides a normalized angle .theta. to a sine/cosine generator that outputs the value of the sine/cosine function at the provided angle. The she/cosine generator in a preferred embodiment comprises a plurality of multiplierless butterfly and carry-save stages in cascade that perform angle rotations on a phasor on the unit circle whose x and y coordinates correspond to cosine and sine values. To calculate the sine and cosine values at a particular angle .theta.=b.sub.1 .theta..sub.1 +b.sub.2 .theta..sub.2 +. . . +b.sub.N .theta..sub.N where b.sub.k .epsilon. {0, 1} are the binary bits and the .theta..sub.k =2.sup.-k are the associated positional weights, each of the butterfly and carry-save stages rotate the phasor by an amount .theta..sub.k =2.sup.-k. The direction of the rotation, clockwise or counter-clockwise, depends upon the value of the binary bits b.sub.k. After undergoing all of the rotations, the phasor has x and y coordinates that approximate the desired cosine and sine values to a specified accuracy. In a preferred embodiment, the datapath of the present invention is multiplierless. The stages for angles where the approximation tan .theta..sub.k =.theta..sub.k is acceptable are multiplierless while for angles where this approximation does not hold, the x and y phasor coordinates are transformed through a multiplexer or a ROM.

REFERENCES:
patent: 4905177 (1990-02-01), Weaver, Jr. et al.
patent: 4910698 (1990-03-01), McCartney
patent: 5142487 (1992-08-01), Graham, III
patent: 5467294 (1995-11-01), Hu et al.
patent: 5521534 (1996-05-01), Elliott

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