Numerically controlled oscillator: Difference between revisions

Revision as of 14:52, 17 February 2015

Revision as of 00:18, 24 May 2015

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===Phase truncation spurs===

The number of phase accumulator bits of an NCO, (N) is usually between 2416 and 64. If the PA output word were used directly to index the PAC look-up table an untenably high storage capacity in the ROM would be required. As such, the PA output word must be truncated to span a reasonable memory space. Truncation of the phase word causes [[phase modulation]] of the output sinusoid which introduces non-harmonic [[distortion]] in proportion to the number of bits truncated. The number of spurious products created by this distortion is given by:

:<math>n_W=\frac{2^W}{\mbox{GCD}(\Delta F,2^W)}-1</math> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(3)