Author Topic: Waveforms in a 74LS04 ring oscillator.  (Read 28454 times)

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #25 on: April 03, 2015, 05:18:56 pm »
Setup a quick test changing from the whiteboard to perf board.    Using same 3 gate ring and buffer.  Added termination.  Didn't have any 450 ohms, so used a couple of 1K 1206s in parallel.   Pulled up the unused gate rather than grounded as shown.

Still a mess, but should speed up the oscillator.   


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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #26 on: April 03, 2015, 05:23:37 pm »
Looked for some other parts to try out.   Was not able to find any HCT or F parts. 

L to R

Motorola SN74LS04N used for previous tests
National MM74HC04N
RCA CD74HC04E
Mototola MC74HC04
Fairchild MB74LS04
ITT 7404

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #27 on: April 03, 2015, 05:27:18 pm »
Shown with the Motorola SN74LS04N.   Notice that the frequency has gone from 41.3MHz on the whiteboard to 46.6MHz on the perf board.  Grounding is much better.   4nS now.  That's a lot of error in the test setup!

« Last Edit: April 03, 2015, 05:32:38 pm by joeqsmith »
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Offline SeanB

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #28 on: April 03, 2015, 05:27:32 pm »
I think that wet tantalum is rather more expensive than the rest of the board though......... Definitely overkill using that 1990's vintage part, though it will still have a low ESR and will still pass all it's military certification tests.
 

Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #29 on: April 03, 2015, 05:30:44 pm »
 ;D   

Shown is the ITT 7404,  5nS

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #30 on: April 03, 2015, 05:37:35 pm »
Well, I tried the Fairchild part and it appears dead.   So next is the RCA CD74HC04E.   3.64nS compared with the Motorola LS at 3.58nS.  Impressive.
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #31 on: April 03, 2015, 05:40:26 pm »
Next is the less impressive Mototola MC74HC04 coming in at 6.24nS.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #32 on: April 03, 2015, 05:43:52 pm »
And last but not least, the National MM74HC04N coming in at 5.92nS.     

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Online T3sl4co1l

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #33 on: April 03, 2015, 05:48:33 pm »
Gotta love the nice sharp pull-up of a CMOS gate, compared to the old weak TTL version... :)
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Offline SeanB

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #34 on: April 03, 2015, 05:48:58 pm »
Now you need to get some ECL devices and try them.
 

Online T3sl4co1l

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #35 on: April 03, 2015, 06:18:21 pm »
Anyone want to start a donation fund for purchasing some Hittite gates? :-DD

"The scope can't tell if it's running... let's point the camera at it and see if it's emitting light instead?"...

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Offline SeanB

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #36 on: April 03, 2015, 06:26:16 pm »
Anyone want to start a donation fund for purchasing some Hittite gates? :-DD

"The scope can't tell if it's running... let's point the camera at it and see if it's emitting light instead?"...

Tim

It only does 28GHz...............

https://www.hittite.com/products/view.html/view/HMC842LC4B

And might go as high as 45GHz.

Don't think dead bud style will work here, and as it is in a ceramic carrier only the price might be a little on the high side. wonder if you can ask AD for a sample device.
 

Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #37 on: April 03, 2015, 07:01:28 pm »
Sorry, I'll have to leave the ECL test to someone else.  My antique stash of TH parts is pretty limited. 

Swapped out the Wavecrapper.  First plot showing the Motorola SN74LS04N, second the RCA CD74HC04E. 

The third plot is an old CMOS 4000 series, Motorola MC14069UBAL.  27.8ns   Way better than I would have guessed.....






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Offline SeanB

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #38 on: April 03, 2015, 07:29:00 pm »
Unbuffered CMOS is always faster, even if it has an output that will barely qualify it as digital. Supply it with 18V and it will be even faster, though it might also run quite hot as well. RCA CMOS was qualified to 20V, as opposed to the 18V of the other suppliers. The rise and fall time is very dependant on supply voltage as well, which can be an issue. 2V supply and most would not work over a few kHz.
 

Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #39 on: April 03, 2015, 08:22:15 pm »
Remember when....  databooks?   Finding the book was faster than searching the internet.  |O 



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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #40 on: April 03, 2015, 08:28:54 pm »
Top is running the MC14069UBAL at 3.3 followed by 10, 15 & 18 volts.   Those wide thresholds made it idea for some applications. 

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Offline albert22

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #41 on: April 04, 2015, 04:47:07 pm »
Here is a similar ring oscillator, by varying the supply voltage they turned it into a VCO. 
What can be expected of something like it?
 

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #42 on: April 04, 2015, 05:11:09 pm »
Seems unlikely that it would be so linear, but it's worth noting a similar thing is used for traditional PLLs and DLLs such as you find in embedded CMOS (MCU / FPGA / radio / etc.) stuff.  What's different is, the gates themselves are controlled from current mirrors (with a cascode circuit), thus varying the slew rate on the switching node (which has a ~constant capacitance), so you'd expect reasonable linearity.

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Offline JoeN

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #43 on: April 05, 2015, 03:15:10 am »
What if this circuit was built out of ECL instead of TTL?  Would that work?  What approximate frequency would you expect to see on the output?  Example IC for implementation:  http://www.onsemi.com/pub_link/Collateral/MC10EL04-D.PDF
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #44 on: April 05, 2015, 04:24:16 am »
Here is a similar ring oscillator, by varying the supply voltage they turned it into a VCO. 
What can be expected of something like it?


Not thinking this would be a real good source but depends what you need.  Even if you ran it closed loop with a little PI controller, hardly seems worth it.

It was easy enough to automate this test with Labview. The data should give you some idea of the open loop non-linearity.  I used the same 3 stage oscillator used for the previous tests.  The power supply voltage was swept from 1.0 to 5.2 volts in increments of 0.1.   To get some decent numbers, a counter running off a GPS was used to measure the output frequency.      I ran all of the same devices.   That old RCA part again looks very good for linearity.   


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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #45 on: April 05, 2015, 05:30:43 am »
Wow, the HC keep going below 1V... (at room temperature, anyway!).  I've heard of them recommended for micropower apps at say 2V, where they're slower than CD4000 at 5V... didn't think they'd keep going that low though.

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #46 on: April 05, 2015, 06:39:53 am »
Found a few more hex inverters in the basement stash.    The Motorola SN74LS14N and MC74HC14AN.  Doubt these will do anything great.  But in the upper left, I found a Fairchild Fast part!   Even the perf board may not be good enough.... 

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #47 on: April 05, 2015, 06:46:28 am »
I have updated the voltage vs frequency graph to include the three new parts. 

Notice the Fairchild F part tops out over 100MHz!  I don't remember anything faster than the Fs back then (in the 7400 series).   Also seem to remember them being more sensitive to ESD.


« Last Edit: April 05, 2015, 07:50:24 am by joeqsmith »
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #48 on: April 05, 2015, 06:56:29 am »
Link to the data sheet:
https://www.fairchildsemi.com/datasheets/74/74F04.pdf

Attached to the LeCroy 8500A with the semi rigid as before.  Sub nS fall times now.  Expected the weaker drive.   

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Offline tggzzz

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #49 on: April 05, 2015, 07:13:00 am »
Now you need to get some ECL devices and try them.

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