Analysis and design of a direct digital-frequency synthesizer with matched differential output

The even harmonics produced by a direct digital-frequency synthesizer (DDS) are excessive. To find a way to overcome this, the theoretical model of center-tapped transformers with differential current output DDS was analyzed. DDS output signals were then simulated. Imbalances between amplitude and phase of DDS output signals were found to increase even harmonics. In order to reduce even harmonics, a method for compensating for the imbalanced amplitude and phase of DDS output differential signals was proposed. The key to the method was the use of unbalanced differential loads. They were used to compensate for the imbalances caused by the DDS, the PCB board, and the transformer. The value of the method was verified by simulations and experimental results.