This paper presents performance of NCO used in Digital Down Converter. Digital Down converter consists of NCO and CIC filter as key components; here the output of the CIC filter is the down sampled version of the input signal. As the sampling frequency at the initial stage is high to reduce the sampling frequency for the further processing, CIC filter is used. The NCO is an implementation of a direct digital frequency synthesizer (DDS) which produces a signal at the output with a specified frequency and phase (adjustable at run time).

1. Xilinx LogiCORE,"Digital Up Converter (DUC) v1. 4", DS276 May 23, 2005 www. xilinx. com
2. Lattice Semiconductor Corporation, "The FPGA as a Flexible and Low-Cost Digital Solution for Wireless Base Stations", A Lattice Semiconductor White Paper, March 2007
3. Matthew P. Donadio, "CIC Filter Introduction", For Free Publication by Iowegian, m. p. donadio@ieee. org, 18 July 2000
4. Pavel KOVAR, "Generation of the Narrow Band Digital Modulated Signals Using Quadrature Digital Up Converter", RADIO ENGINEERING, VOL. 12, NO. 1, APRIL 2003
5. Direct digital synthesis (DDS) http://www. radioelectronics. com/info/receivers/synth_basics/dds. php
6. QAN19 Modulating Direct Digital Synthesizer in a quick logic FPGAhttp://www. quicklogic. com/images/appnote19. pdf (Accessed on April 10, 2006)
7. Eva Murphy and Colm Slattery, "All about Direct Digital Synthesis", Analog dialogue 38-08, August 2004, http://www. analog. com/analogdailogue
8. Xilinx LogiCORE,"Multiply Accumulator v4. 0", DS336 April 28, 2005 www. xilinx. com
9. Cyril Prasanna Raj P and Subash, "SASTech Journal", Vol 4. PP 33-39, September 2006
10. S. Signell, T. G. Kouyoumdjiev, K. H. Mossberg, "Design and Analysis of Bilinear Digital Ladder Filters", IEEE Trans. on Circuits and Systems, Vol. 43, No. 2. , February 1996.
11. E. B. Hogenauer, "An economical class of digital filters for Decimation and interpolation IEEE Trans. on Acoustics, Speech. And Signal Processing, Vol. 29, pp. 155-162, April 1981.

Digital Down Converter