[time-nuts] from Sputnik to CD

J.D. Bakker jdb at lartmaker.nl
Tue Oct 9 06:58:10 EDT 2007

>Finding actual plots of the effect of clock jitter on effective DAC SNR
>etc is somewhat problematic however the attached plot from
>illustrates the clock jitter sensitivity of some sigma delta DAC designs.

There's a LOT of hand waving in that article, and very little 
substance. The author has an extremely roundabout way of saying 
'jitter performance is proportional to signal amplitude', and NO 
commercial converter that I know of would dream of reducing output 
amplitude in order to alleviate the impact of jitter. What is the 
test frequency used in producing the plot you've linked ?

I find it quite a leap to conclude that for a switched-cap 
architecture (effectively an integrator) "[w]hen the clock jitter is 
less than 60 ns [...] VOUT is constant". I admit that my experience 
is chiefly with ADCs, but I've seen very little difference in 
measured jitter performance between top-of-the-line single bit (SACD) 
and multibit (PCM) S/D audio ADCs from Cirrus, TI and Sony/Philips, 
and none of them manage to 'cheat' their way out of the predicted 
2*pi*f*A*Tjitter high-jitter performance like Figure 3 seems to 
imply.  I'd love to test the AKM offerings too, but they're next to 
impossible to get in small quantities.


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