Hello, on the 18th page of AD9858 datasheet, there is a formula to calculate DFTW, which is

t=abs(fF-fs)*2^34/sysclk^2*DFRRW/DFTW

but when i use the DFTW result got from this equation (t, abs(fF-fs) and DFRRW are known) to control the DDS, i always get only half the abs(fF-fs). Should this equation be

t=abs(fF-fs)*2^35/sysclk^2*DFRRW/DFTW

Thanks very much!

Hi Yake,

I think it has something to do with the model the equation is used. Like it only considers from Fs to Ff. So if it is Fs to Ff and Ff to Fs then you'll have to correct the equation by two. Was this the case?

Best Regards

Louijie