Fox Electronics XpressO VCXOs and XOs

twest820

Member
2009-06-24 10:49 pm
(old thread, but I'm considering using XpressO parts in a build and this is by far the most appropriate of two DIYA threads which mention them)

Seem to offer good bang for the buck. Not by a wide margin relative to competing parts but Fox's pads appear to have the advantage of coming up the side of the package. Should make for easier DIY soldering than the typical underside only LLC arrangement.

Anyone else looked at the XpressOs in, oh, the past three years or so? ;)
 
Just from looking at the datasheet , these Fox oscillators don't appear to be best for digital audio clock generation. The key figures are the 'close-in' (1Hz up to about 10kHz) phase noise shown in the phase noise plot. The phase noise is rather high in that region, which will directly translate in to highish random jitter at those same frequencies. For comparison have a look at the close-in phase noise plot for the T.I. CDCS502 shown in it's datasheet.
 

twest820

Member
2009-06-24 10:49 pm
No, they're not the best. But then they don't cost USD 30 each, either. Nice find on the CDCS502---most datasheets don't have a phase noise spec so it's difficult to reason about whether they'd perform better or worse than the XpressOs. At the lower cost end of the range the overall jitter figures on competing parts are higher, sometimes significantly so, and some parts don't even have jitter specs. For example, the CDCS502 datasheet states 100ps cycle to cycle jitter. But not the measurement conditions or whether that figure is peak cycle to cycle or some other metric. If one assumes it's peak cycle to cycle it's probably reasonable to compare it to the XpressOs' total jitter figure of 26ps. In which case the CDCS502 may result in worse performance than the XpressOs despite its lower level of phase jitter. It's been quite a while since I had access to a jitter scope so sampling the two parts and taking measurements to enable direct comparison unfortunately isn't really an option for me.

My experience in ambiguous situations such as this is parts with more complete characterization information in the datasheet tend to work better. That's just a rule of thumb though.
 

twest820

Member
2009-06-24 10:49 pm
I don't; one of the handy things about operating ESS DACs in asynchronous/oversampling mode is the freedom to pick among the FXO-HC73s Digikey or VCC1-B3s Mouser has for cheap. ;)

45.158 is a standard VCC1 frequency so I'd email/call Mouser/Vectron and inquire about availability.
 
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> one of the handy things about operating ESS DACs in asynchronous/oversampling mode is the freedom to pick among the FXO-HC73s Digikey or VCC1-B3s Mouser has for cheap

So obviously you have not heard the ESS in synchronuous mode, and compared to asynchronuous.

http://www.diyaudio.com/forums/digi...ng-new-ess-vout-dac-es9022-2.html#post2484647

> Another option is the Crystek CS3392 (if it has the frequency you need).

No 45.1584 from Crystek.

> Take a look at the Guido Tent (Tentlabs) offering.

I know what he has, won't fit.


Patrick