Lockheed Martin Corporation

Douglas A Leonard, Jr

Peter L Delos

A method of producing a low spurious output signal in a frequency generator circuit comprises, in a direct digital synthesizer (DDS), generating a signal at a first frequency; mixing the signal to produce a signal at a second frequency in an operating band of interest higher than the first frequency; determining spurious signals in the second frequency signal due to non-linearity in a digital to analog converter (DAC) of the DDS; generating at least one amplitude and frequency vector containing information relating to an amplitude value and frequency value representative of one of the determined spurious energy signals; generating a pre-distortion signal based on the at least one amplitude and frequency vector; and combining the pre-distortion signal with the signal generated by the DDS to produce a corrected output signal, wherein the pre-distortion signal is phase offset from a corresponding determined spurious signal to cancel the corresponding determined spurious signal.

Method for reducing direct digital synthesizer (DDS) and mixer spurious

A waveform generator circuit provides low spurious output signal and includes a primary DDS for generating a RF signal at a first frequency. A DAC receives an output signal from the primary DDS and converts the digital DDS output to an analog output. A spectrum analyzer identifies spurious signals in the DAC output determining the amplitude and frequency characteristics of the spurious signals. The waveform generator includes at least one cancellation DDS configured to generate a pre-distortion signal corresponding to frequencies where spurious signals are expected due to non-linearities in the DAC circuitry. The pre-distortion signals are phase offset from the determined spurious signals to cancel the spurious signals. The pre-distortion signals are combined with the output of the primary DDS. The combined signal contains the primary DDS output signal and pre-distortion signals to produce an analog output signal which cancels out the expected spurious signals.

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Cherry Hill, NJ, United States of America

Douglas A Leonard, Jr