Ultra Low Phase Noise DSP Oscillator [DSP Tips & Tricks]

This article describes a novel complex oscillator, which is based on an interesting variation of the traditional CORDIC DDS and produces sine and cosine output samples of any specified angle. Our oscillator provides drastically improved phase noise performance (relative to a traditional CORDIC DDS) without the need for additional CORDIC iteration processing. In addition, our oscillator supports real-time output sample-by-sample digital frequency control. In describing our enhanced complex oscillator, we first present the arithmetic processing needed to generate sine and cosine samples. Next we show how that processing is implemented using the CORDIC algorithm. Then we detail the trick used to reduce oscillator phase noise errors. Finally we show how to guarantee a stable oscillator output amplitude and present an example of our oscillator's ultra low phase noise performance.