Spurious suppression in direct digital synthesizers

A method is proposed for the removal of discrete line spurs normally present in the output of direct digital synthesizers (DDS). The method involves random varying, or dithering, the periods of the alternating output, while keeping the average of these periods unchanged. Details involved in the dither process and expressions for deriving the expected value of carrier power to noise density of this synthesis technique are described. Also, expressions useful in determining the noise density associated with square waves that exhibit edge time jitters are provided. Tests on a breadboard DDS constructed of low-power Schottky logic confirm predictions of the analysis.