Technology Research, Based On The Dds Frequency Synthesizer Spurious Suppression

In this paper, we shall introduce the structure, basic principle and ideal frequency spectrum of direct digital frequency synthesizer (DDS), and conclude some sources of output spurious signals in DDS. Then in the light of their properties, we adopt the method of time-domain waveform to analyze these influence generated by the phase truncation and amplitude quantization in the output spectrum and provide the distributed pattern of their error frequency spectrum. With the assistance of computer simulation, we test the conclusion.In the next part, we shall discuss some novel methods to improve the output signal.First, we employ phase-dithering method. Spur reduction is accomplished through dithering phase values prior to word-length reduction. This means provide a spur reduction from 6dB to 12dB per phase bit. While the spur reduction is at the expense of an increase in system noise, the noise can be made white, making the noise power spectral density small. This technique permits the use of a smaller number of phase bits addressing sinusoid look-up tables, resulting in an exponential decrease in system complexity.Second, we make a circuit with the method of DDS+PLL. The way of DDS driving PLL can take good advantage of both their merits: the high resolution, high accuracy, convenient control of frequency variance for DDS and the excellent character of narrow band tracing filtering for PLL. We introduce the arrangement and realize the circuit.Third, we discuss a phase-interpolation direct digital synthesizer with an adaptive integrator. Unlike a conventional DDS, it does not use ROM or a D/A converter. Therefore less power is dissipated and the maximum speed is increased. We believe that these targets will be the key of wireless communication...