A Numerically Controlled Oscillator with a Fine Phase Tuner and a Rounding Processor

ETRI Journal

关键词: rounding processor;    fine phase tuner;    look-up table;    sine wave generator;    Numerically controlled oscillator(NCO);   

Others  :  1185013
DOI  :  10.4218/etrij.04.0204.0026

【 摘 要 】

We propose a fine phase tuner and a rounding processor for a numerically controlled oscillator (NCO), yielding a reduced phase error in generating a digital sine waveform. By using the fine phase tuner presented in this paper, when the ratio of the desired sine wave frequency to the clock frequency is expressed as a fraction, an accurate adjustment in representing the fractional value can be achieved with simple hardware. In addition, the proposed rounding processor reduces the effects of phase truncation on the output spectrum. Logic simulation results of the NCO using these techniques show that the noise spectrum and mean square error (MSE) for eight output bits of a 3.125 MHz sine waveform are reduced by 8.68 dB and 5.5 dB, respectively, compared to those of the truncation method, and 2.38 dB and 0.83 dB, respectively, compared to those of Paul’s scheme.

   

【 参考文献 】

• [1]Henry T. Nicholas, III, Henry Samueli, Bruce Kim, "The Optimization of Direct Digital Frequency Synthesizer Performance in the Presence of Finite Word Length Effects," Proc. 42nd Annual Frequency Control Symposium, June 1988, pp. 357- 363.
• [2]R. Ertl and J. Baier, "Increasing the Frequency Resolution of NCO-Systems Using a Circuit Based on a Digital Adder," IEEE Trans. Circuits Systems II: Analog and Digital Signal Processing, vol. 43, Mar. 1996, pp. 266-269.
• [3]Paul O’Leary and Franco Maloberti, "A Direct-Digital Synthesizer with Improved Spectral Performance," IEEE Trans. Communications, vol. 39, no. 7, July 1991, pp. 1046-1048.