Double Quadrature Mixer for adaptive spur cancellation in ultra-wideband radios

Direct Digital Synthesizers (DDS) are known to be very spurious due to the use of Digital-to-Analog Convertors (DAC). This paper presents the phase behaviour of spurs of the AD9912 DDS and its SpurKiller cancellation system. A great variation in spur phase and a variation in increased spurious-free dynamic range (SFDR) was observed. As a result, an adaptive system is proposed using a Double Quadrature Mixer and a variable phase LO. The system is tested at the Intermediate Frequency (IF) of 1.2 GHz, simulating an Ultra-Wideband (UWB) radio. In simulation, an increase in SFDR of 29 dB resulted. In system prototype, an increase in SFDR of 10 dB resulted.