Error feed-forward direct digital synthesis
AssigneeXilinx, Inc.
InventorsChristopher H. Dick, Frederic J. Harris
Life of this patent
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Abstract
A circuit arrangement and method for direct digital synthesis (DDS). In various embodiments, the invention feeds forward the phase error introduced by a quantizer in a DDS system. The error is fed forward to adjust the sine and cosine values that are obtained based on output from the quantizer. Correction of the sine and cosine values based on the fed-forward error values results in a significant reduction in the effect of spectral artifacts.
Claims20
A circuit arrangement for direct digital synthesis, comprising:
- a phase accumulator having an input port and an output port;
- a quantizer having an input port and an output port, the input port coupled to the output port of the phase accumulator;
- a lookup table having first and second output ports and an input port coupled to the output port of the quantizer, the lookup table configured and arranged to output on the first output port a first value being a sine function of an input value to the lookup table and output on the second output port a second value being a cosine function of the input value;
- and
- a feed-forward error-correction circuit having input ports coupled to the output ports of the phase accumulator, the quantizer, and the look-up table, the error-correction circuit arranged to determine the error as a function of an input value to and an output value from the quantizer, and to correct the error as a function of output values from the lookup table.
A method for performing direct digital synthesis, comprising:
- accumulating phase increment values, whereby a sequence of accumulated phase values is generated;
- quantizing the accumulated phase values, whereby quantized phase values are generated;
- generating initial sine values and cosine values from the quantized phase values;
- determining phase error values introduced in the quantizing step;
- and
- generating corrected sine values and cosine values as functions of the phase error values and initial sine and cosine values.
A circuit arrangement for direct digital synthesis, comprising:
- a phase accumulator having an input port and an output port;
- a quantizer having an input port and an output port, the input port coupled to the output port of the phase accumulator;
- a subtracter having an output port and input ports coupled to the output ports of the phase accumulator and the quantizer;
- a constant coefficient multiplier having an output port and an input port coupled to the output port of the subtracter;
- a lookup table having first and second output ports and an input port coupled to the output port of the quantizer, the lookup table configured and arranged to output on the first output port a first value being a sine function of an input value to the lookup table and output on the second output port a second value being a cosine function of the input value;
- a first multiplier having an output port and input ports coupled to the constant coefficient multiplier and the first output port of the lookup table;
- a first adder having an output port and input ports coupled to the output port of the first multiplier and the second output port of the lookup table;
- a second multiplier having an output port and input ports coupled to the constant coefficient multiplier and the second output port of the lookup table;
- and
- a second adder having an output port and input ports coupled to the output port of the second multiplier and the first output port of the lookup table.
Dependencies are inferred from the claim text.