Frequency divider (divide by 100)

schreef in bericht news: snipped-for-privacy@4ax.com...

A 74HC390 will do, but you'll need a high speed comparator to obtain a good logic clock signal. Consider an NE529 or a MAX975. A circuit like this will have no drift but you may encounter jitter. This will mainly depend on the quality of your input signal but may be influenced by the comparator circuit.

petrus bitbyter

And if you're using a single supply comparator like the MAX975, you may want to use the HP3325B auxillary Sync Output (square wave output, HI

square wave has great rise and fall times for your comparator conversion to TTL and then the HC390 (remember, /2 last if you want a 100KHz square wave).

Don't worry, it's digital -- there will be _no_ frequency error from the /100 section. Your propagation delays should be consistent too.

Good luck Chris

Yes indeed.

Correct. You need a comparator to give you a square wave for your 390. I've done exactly that with a MAX4212, but there are plenty of others that will work fine.

You already have the easiest way.

Correct. There should be no frequency error, no phase error, and no drift error. You will however get a small amount of jitter on top of what your 10MHz source signal already has, but that won't be an issue in your case.

I have done this to characterise the long term drift of a DTCXO oscillator module using a 10MHz sine wave Rubidium frequency standard. Email me if you want the circuit.

Dave :)

square wave has great rise and fall times for your comparator conversion to TTL and then the HC390 (remember, /2 last if you want a 100KHz square wave).

I haven't checked, but will the sync output vary when you change the phase on the 3325b? If it doesn't, then I don't need the circuit at all, and just can compare phase of the sync to the output. I'll have to check tomorrow.

square wave has great rise and fall times for your comparator conversion to TTL and then the HC390 (remember, /2 last if you want a 100KHz square wave).

Just checked today, the sync varies in phase w/ the output signal, so I can't use it for the reference phase. Thanks for the idea though. The reference signal is a 10MHz sine wave from an HP 58540A gps receiver, do you think this will be adequate to drive a comparator for a stable square wave out?

Thanks for all your help everyone.

Steve

That square wave has great rise and fall times for your comparator conversion to TTL and then the HC390 (remember, /2 last if you want a 100KHz square wave).

Hi, Steve. I'm not familiar with the HP58540A -- you might want to glance at the manual.

Petrus' original idea is a good one. Just make sure you terminate the signal properly, and try it. If you get clean logic transistions at the comparator output, you should be done. If not, please feel free to post back.

Good luck Chris

I'm having troubles. I want to use this whole circuit at a single +5V supply to simplify things. The only two comparators I have handy are an LM219D and an LM360. It appears (though I haven't actually experimented), that the LM360 won't run off that low a voltage on a single supply (the datasheet states minimum -4.5/+4.5). The LM219D seems to run fine off the single 5V, but I can't get good logic output above around 250-300kHz. At 10MHz, I can't get anything out besides either pegged at +5 or 0 w/ 10MHz noise (based on how I bias the comparator/input amplitude, etc...). Is this based on the fact that it's only rated for 80ns at +-15V, and that I'm using a sine wave input? Is there a better comparator that's readily avaliable in small quantities (

Hi, Steve. Could you describe a little more about your situation? There are many ways to square up a 2-3VRMS sine wave into a stable digital logic signal, particularly if you're not too picky about 50% duty cycle.

For one thing, it's fairly easy to do the level translation with a diode, transistor, and a couple of resistors if you have a low impedance signal source (view in fixed font or M$ Notepad):

| | VCC | + | | | | | .-. | 1K| | | | | '- | | | o--------->

| | | ___ |/ | o------o->|-o-|___|-| 2N4401 | | | 220 |>

| 50 ohm| | | | .-. .-. | | | | | |220 | | | | | | | | '-' '-' | | | | | | | | | | o------o----o---------o | | | === | GND | (created by AACircuit v1.28.6 beta 04/19/05

You may have to tweak the resistors a bit to be sure you get a good

1-0-1-0 logic level here. This depends on the amplitude of your signal (you may need an additional gain stage if the level varies by a lot. Now if you had a veritable panoply of HC ICs available, you would then just use a 74HC14 to give you a squared off logic signal for your comparators. The 15ns propagation delay is sufficient for a 10MHz pulse.

But actually, that probably isn't necessary. As long as your clock pulse width exceeds 30ns (check!), you should be OK. The HC390 is fairly forgiving on clock rise and fall times, at least on this time scale.

Good luck Chris

Oh, yes -- diode 1N914 or equivalent signal diode -- don't use a 1N4001 here.

Chris

I'm probably getting confusing at this point. I'll try to clairfy. I have a 10MHz oscillator reference (the GPS receiver) feeding into a

5087a distribution amplifier which is our main timebase for all the equipment. Therefore I can adjust the amplitude of the signal relitavely easily, but I would rather design the circuit to input a range of around 2-3VRMS, that way I can use any of the outputs from the amplifier because they are all adjusted within that range at this point, and we change around our equipment from different outputs often. I need to convert this 10MHz signal into a 100kHz signal. The shape of the 100kHz signal isn't necessarily important, as long as it is stable (no phase or frequency drift). That's pretty much it. I was going to use the HC390 for the divider, of course, and that part seems fine. I'm just working on the 10MHz TTL clock. That circuit you have looks promising. I had just input the sine directly into the comparator with the inverting input at a level of around 1VDC, and the sine wave of a level of appx 4VPK, (8VP-P). I'm not much of a design engineer, as you can tell, I mostly work on repair & cal of avionics.

Thanks for all your help, I'll build up that circuit tonight and post back.

Steve

Use the Maxim parametric guide on the website to find a suitable device rated for single rail operation, and then order some free samples ;-) Start here:

Dave :)

--
From:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

"Summarize what you\'re following up.

When you click "Reply" under "show options" to follow up an existing
article, Google Groups includes the full article in quotes, with the
cursor at the top of the article. Tempting though it is to just
start
typing your message, please STOP and do two things first.  
Look at the quoted text and remove parts  that are irrelevant. 
Then, go to the BOTTOM of the article and start typing there.
Doing this makes it much easier for your readers to get through your
post.  They\'ll have a reminder of the relevant text before your 
comment, but won\'t have to re-read the entire article.  
And if your reply appears on a site before the original article
does, 
they\'ll get the gist of what you\'re talking about."

Sorry, I suppose I cut too much text out (all of it in this case, oops) and the original conversation was lost. Apologies to all for the confusion.

Steve

Good idea, I guess I'm just not too well versed at desigining circuits and selecting products. I'm more used to building pre-engineered circuits, but I really would like to expand my knowledge and experience. Thanks for the advice.

Steve