My[1] scope can't measure jitter directly either (despite having the "advanced math module"[2]), but there's no shame in the cursor method.[3]
-jwb
1: "My" being the scope I have at the office, not the amazing Tek 465 at home.
2: Advanced math apparently means addition, subtraction, and multiplication.
3: Set the scope to accumulate or high intensity and use the cursors to find the excursion on the time axis.
-jwb
1: "My" being the scope I have at the office, not the amazing Tek 465 at home.
2: Advanced math apparently means addition, subtraction, and multiplication.
3: Set the scope to accumulate or high intensity and use the cursors to find the excursion on the time axis.
Huh, err... And that way you want to measure down to 1 ps ??? Hopefully your scope’s time base has that low jitter too. A better approach would be to build two identical oscillators. Feed them to a mixer and measure the sideband noise with your soundcard and a FFT program. I am just thinking of this. But maybe it is easier to contact some old colleagues from the university to dig up a nice new Tek TDS scope.
That will give you a phase noise measurement, which will not be the same as a jitter measurement. Jitter measurements take into account voltage variations from ground bounce, Vcc shift, and stuff like that. Those fancy 'scopes have fancy A/Ds that are supposed to be good for that. But then they can cost $40K. For that price, they ought to be good.
Jocko
Jocko
True Jocko,
But about what are we talking here? Jitter of the oscillator or conversion-clock jitter at the DAC?
RMS jitter and sideband noise are closely related if it concerns an oscillator. If you measure the sideband noise you can calculate the RMS value of the jitter. It’s true you can’t measure the pp value of the jitter that way.
Note that if an oscillator is specified for say 5 ps jitter it is most time given in RMS. The pp value can easily be as high as 20 ps to 50 ns.
But why does anyone want to measure the numerical value of the jitter if you can listen to the musical result? Measuring is only handy to see if you make progress on a testbed. Relative measurements will suffice then. If you look at the down converted sideband spectrum, the sideband lobe need to be as narrow as possible and the white noise floor as low as possible. If you want to investigate psu-related noise you need to power each oscillator from different psu’s to avoid correlation of the psu noise.
But about what are we talking here? Jitter of the oscillator or conversion-clock jitter at the DAC?
RMS jitter and sideband noise are closely related if it concerns an oscillator. If you measure the sideband noise you can calculate the RMS value of the jitter. It’s true you can’t measure the pp value of the jitter that way.
Note that if an oscillator is specified for say 5 ps jitter it is most time given in RMS. The pp value can easily be as high as 20 ps to 50 ns.
But why does anyone want to measure the numerical value of the jitter if you can listen to the musical result? Measuring is only handy to see if you make progress on a testbed. Relative measurements will suffice then. If you look at the down converted sideband spectrum, the sideband lobe need to be as narrow as possible and the white noise floor as low as possible. If you want to investigate psu-related noise you need to power each oscillator from different psu’s to avoid correlation of the psu noise.
The thermal phase noise of the oscillator, and the jitter introduced by the circuitry that follows, that can degraded its performance.
I prefer the noise spectrum method, but it would be nice to have a fancy 'scope that could give a quick check of the amount of deviation in pS. The noise spectrum will give you more insight, from a design standpoint. Which I would find more interesting.
Jocko
I prefer the noise spectrum method, but it would be nice to have a fancy 'scope that could give a quick check of the amount of deviation in pS. The noise spectrum will give you more insight, from a design standpoint. Which I would find more interesting.
Jocko
Exotic 'scopes
Unless anyone has a 'scope that is capable of measuring jitter, don't bother.
Triggering the 'scope on the jittered signal gives misleading results, related to the 'scope trigger interval and the transition interval being measured.
The frequency spectrum also has an effect, at some frequencies jitter will not be shown at all, and at others it could appear doubled in amplitude, what one is really displaying is interval variations.
Andy.
Unless anyone has a 'scope that is capable of measuring jitter, don't bother.
Triggering the 'scope on the jittered signal gives misleading results, related to the 'scope trigger interval and the transition interval being measured.
The frequency spectrum also has an effect, at some frequencies jitter will not be shown at all, and at others it could appear doubled in amplitude, what one is really displaying is interval variations.
Andy.
Seems like the main trick here is going to be clean power supplies. The oscillator obviously needs one (9V) and the inverter or comparator needs a different one (5V). I guess I'll derive the latter from the former.
Also I suspect that the comparator will have better PSRR than the inverter for turning sine into square. With the inverter, any supply noise is going to translate directly into timing errors on the output. But with the comparator the reference voltage can be set with something quiet (LED, buried zener, etc.).
Also I suspect that the comparator will have better PSRR than the inverter for turning sine into square. With the inverter, any supply noise is going to translate directly into timing errors on the output. But with the comparator the reference voltage can be set with something quiet (LED, buried zener, etc.).
? on BJT's
Hi Jocko,
I've etched a small board for the oscillator and destroyed yet another shirt with ferric chloride stains...(the schematic with the power supply) and am in the processs of stuffing it. But I have a question on BJT's...
I'm using Zetex 694b's and 795a's in place of the 2sc2240's and 2sa970's, these seem to match up pretty well, but what is the reason for using these very high hfe types, just curious.
Also is there anything specific to keep in mind if substituting for the 2sd438's? I have a ton of MPS8099's from a Leach amp project....(yes I've read the new law) I'd be more than happy to use something better, but I'm not sure what I'm looking for in this application?
Thanks again,
Pete Kunz
Hi Jocko,
I've etched a small board for the oscillator and destroyed yet another shirt with ferric chloride stains...(the schematic with the power supply) and am in the processs of stuffing it. But I have a question on BJT's...
I'm using Zetex 694b's and 795a's in place of the 2sc2240's and 2sa970's, these seem to match up pretty well, but what is the reason for using these very high hfe types, just curious.
Also is there anything specific to keep in mind if substituting for the 2sd438's? I have a ton of MPS8099's from a Leach amp project....(yes I've read the new law) I'd be more than happy to use something better, but I'm not sure what I'm looking for in this application?
Thanks again,
Pete Kunz
Re: ? on BJT's
Check here for alternative etching method.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=6594&highlight=h2o2
pjkunz said:
Check here for alternative etching method.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=6594&highlight=h2o2
Well,
some years ago I build my own XVCO-oscillator (for my DAC).
I suggest :
1 : no power noise should influence each other gain stage
- R/C each power/gain element separatly
- R/C may also the base separatly
2 : Grounding & shielding: build each gain part in an separated 0.5...1mm cu box (military alike) and use the box as the ground
result : no magnetic or electric RF should go in/out and interference with other parts.
3: use smd parts (trans. I used 2n918 alike smd)
4: no trimm-elements, first measure and then replace with related
smd cap's
5: use for power connection a pass-trough caps to keep
the nois within the cu box
well life it's not so easy in the rf field...
may I helped in the right direction....
Cheers,
HpW
some years ago I build my own XVCO-oscillator (for my DAC).
I suggest :
1 : no power noise should influence each other gain stage
- R/C each power/gain element separatly
- R/C may also the base separatly
2 : Grounding & shielding: build each gain part in an separated 0.5...1mm cu box (military alike) and use the box as the ground
result : no magnetic or electric RF should go in/out and interference with other parts.
3: use smd parts (trans. I used 2n918 alike smd)
4: no trimm-elements, first measure and then replace with related
smd cap's
5: use for power connection a pass-trough caps to keep
the nois within the cu box
well life it's not so easy in the rf field...
may I helped in the right direction....
Cheers,
HpW
The 'D438 is there because a little package will get too warm. At least it will if you put 50 mA through it. You could use whatever NPN that works well in the oscillator if you can get the heat out of it.
The Zetex ones should work. You will not have to recalculate anything. Except maybe the base divider, to get lots of current through th common-base stage.
The reason is that they have narrow base regions, and should have good gain, bandwidth, and low noise.
SMT would be nice.
Someday I will post a Butler version. Problem is getting enough voltage out of one with low distortion. (Yeah, I know.....it will be squared up somewhere, and lots of harmonics then. I want it to be low harmonic, so that it can be piped all over the shop without generating EMI.)
Jocko
The Zetex ones should work. You will not have to recalculate anything. Except maybe the base divider, to get lots of current through th common-base stage.
The reason is that they have narrow base regions, and should have good gain, bandwidth, and low noise.
SMT would be nice.
Someday I will post a Butler version. Problem is getting enough voltage out of one with low distortion. (Yeah, I know.....it will be squared up somewhere, and lots of harmonics then. I want it to be low harmonic, so that it can be piped all over the shop without generating EMI.)
Jocko
Thank you. I forgot about MCM. Is it worth (a realtive term, I know) ordering the toshiba parts instead of th Zetex parts I have now? The Zetex datasheets don't list noise specs. How much, if any, difference/degredation will there be with the Zetex parts. I'd rather do it once and do it relatively right (drilling boards is a pain..) , eventually I may do this in SMD but the other item on my plate (trying to graduate...finally, 12 years of college is a bit much for anybody) is dominating my landscape right now. Any insight is appreciated as is the amount I'm learning from this little project.
Thanks,
Pete Kunz
Thanks,
Pete Kunz
Low Phase Noise oscillator
Hi All, I find this thread quite amusing as if there never excisted a KWAK-CLOCK.
Powersupply does make make a difference but it is only a minor effect. The "secret" of the KWAK-CLOCK is in the FET and the comparator in other words in the schematic.
Just hit the e-mail button underlining this post and you will get the schematic. Professionals get version 6. Others version 5. Decide for yourself which catagory you belong.
Hi All, I find this thread quite amusing as if there never excisted a KWAK-CLOCK.
Powersupply does make make a difference but it is only a minor effect. The "secret" of the KWAK-CLOCK is in the FET and the comparator in other words in the schematic.
Just hit the e-mail button underlining this post and you will get the schematic. Professionals get version 6. Others version 5.
Decide for yourself which catagory you belong.
Hi Elso. You may take some education from this. The reason there is interest in this oscillator is because it is out in the open. The schematic is posted by Jocko, and we can all evaluate it. We can discuss it on common terms.
With your Kwak-Clock, the schematic is only available by email. It is very mysterious. It is not "out there".
With your Kwak-Clock, the schematic is only available by email. It is very mysterious. It is not "out there".
Re: KWAK-CLOCK/ Education?
Don't be a bitterman, Elso. You can't deny that posting a schematic generates discussion. If you want people to discuss your oscillator instead of Jocko's, you need to post the schematic.
In the thread you linked, the only schematics were posted by Jocko, ftorres, and som others. There are exactly zero schematics of the Kwak-Clock.
Elso Kwak said:
Don't be a bitterman, Elso. You can't deny that posting a schematic generates discussion. If you want people to discuss your oscillator instead of Jocko's, you need to post the schematic.
In the thread you linked, the only schematics were posted by Jocko, ftorres, and som others. There are exactly zero schematics of the Kwak-Clock.
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