In article <1139426514.841712.37900@f14g2000cwb.googlegroups.com>, Ron N. <rhnlogic@yahoo.com> wrote:>Mark wrote: > >> A software PLL is based on an NCO and an NCO unlike a VCO has a minimum >> step size so it can only achieve a number of discrete frequencies, i.e. >> the output frequency is quantized. > >Why do you say this?Perhaps because this is what he has seen.> An NCO is, of course based on some digital >number representation; but if you use IEEE doubles, the quantization >error of the phase is much smaller than the thermal noise of any >analog oscillator, maybe even smaller than the quantum limits >physics allows any analog VCO.IEEE doubles requires some serious amount of electronics and is not really the best way to go. You do better with a 64 bit fixed point system. I've done quite a few digital PLL systems and have never needed to go beyond about 32 bits to get good results. Still if you are making a square wave on the output you have 1 clocks worth of jitter. -- -- kensmith@rahul.net forging knowledge
Re: Software PLL (SPLL)
Started by ●February 8, 2006
