Author Topic: Waveforms in a 74LS04 ring oscillator.  (Read 28127 times)

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Online tggzzz

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #50 on: April 05, 2015, 07:14:31 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.

I was more surprised at the voltage at which the LS device ran.
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #51 on: April 05, 2015, 07:42:30 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.

Tim

At least the two parts from Motorola and National did.  The RCA fell a little short.   

Plot showing the Fast part running at 5.4 volts stuck to a Peltier then cooling it.     With a little higher voltage and a little more cooling, it may break 110MHz.   

 

 
« Last Edit: April 05, 2015, 07:50:58 am by joeqsmith »
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #52 on: April 05, 2015, 07:55:56 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

That seems like a good experiment for you to try and then post your findings.   

I was trying to stick with the same pinout and package that the OP was using.       
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Offline SeanB

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #53 on: April 05, 2015, 08:22:27 am »
I remember some boards that used a 74F 138 as a logic decoder, just so they could get those extra few ns of propagation delay down, so that they could use a slower and much cheaper SRAM device. Important if you were making a 128k bank switched ram board and wanted the slower RAM battery backed, the difference in leakage current for the slow parts as compared to the faster ones was actually quite significant. Still ran at sub 4MHz though, using a Z80 processor. There was a note in the service manual that you had to use a F device in those address decoder locations, and use LS or S chips in the rest of the decode logic as well. Supply fail was detected with a simple transistor and zener diode fed from the 8V logic supply, so you would write protect the RAM array when the 8V bus fell to 6V. The transistor drove a CMOS inverter that simply deselected the alternate chip select, putting the RAM to low power mode.

Those days when a 6116LP3 chip was considered both a large chip and a low power one as well.
 

Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #54 on: April 05, 2015, 05:53:27 pm »
I have an old HP6285A 6A 20V power supply connected to a HP59501B power supply programmer.   Very crude setup but the price was right.   I built this little adjustable clamp that I use to protect the parts in case of a software bug or me pushing a wrong key.   

I wanted to see how stable the F ring was.   Put the assembly in my calibrated towel, tuned it on and let it sit for an hour.




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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #55 on: April 05, 2015, 05:58:06 pm »
After the hour warmup, I collected data for an hour.    The frequency drifted almost 250KHz.  Lower graph is showing the power supply drift, about 2mV.   Keep in mind from previous data, frequency went up with voltage, not down.   Suspect this is more temperature than anything.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #56 on: April 05, 2015, 06:01:25 pm »
From the data sheet, the F part will handle up to 5.5 volts.   To show the effects on the frequency with voltage, I stepped it up few times.  Notice how it jumps in frequency then slowly drops off.     
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #57 on: April 05, 2015, 06:09:25 pm »
I pushed the supply up higher, then took a cotton swap with alcohol on it, at dabbed it onto the IC.  You can clearly see how the temperature effects the frequency.   To see if the part would break 110MHz, I raised the voltage to 5.500.  This was not enough even with the alcohol.   

Placed the Peltier on a fair sized heat sink and laid it over the IC.  To the right, you can see the oscillator speeding up well beyond 110MHz as it is cooled.  Final temp was +12C.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #58 on: April 07, 2015, 02:47:21 am »
I had no plans to test more parts, until I uncovered more parts.....   I was hunting for some ECL but the only thing I found was a TTL translator.     

New are the ACTs from Motorola and Harris.  Also a Fairchild HC and a National 4069CN.  Not sure if that is a buffered part or not.   

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #59 on: April 07, 2015, 02:55:13 am »
Before testing the new parts, I wanted to see if there was any more speed gains in the F ring oscillator with temperatures below +12C.     Next few pictures show my free temperature chamber I  put together tonight.

Old computer heatsink.  Thermal epoxy the peltier to the heat spreader.   Epoxied aluminum block to the peltier.




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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #60 on: April 07, 2015, 02:57:36 am »
Small hole in the block is for the K sensor.  Open air, -11C.   Block gets a bit of frost on it.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #61 on: April 07, 2015, 03:00:27 am »
Built up a few layers of insulation.  Hot glued together.   Insulation block on the cover is used to press the perf board (IC lid) against the aluminum block.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #62 on: April 07, 2015, 03:14:01 am »
After all of that, the results were less than impressive.   With the F part running at 5.5 volts, I can now get the temperature down to -7C, or about 19 degrees lower than before.     The speed was a wash at 110.97MHz. 

I then heated the part to 50C and kept the voltage at 5.5.   After it stabilized, it was around 104.28MHz.   

A lot more stable than I would have guessed. 




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Offline dannyf

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #63 on: April 07, 2015, 11:13:47 am »
Those are really good numbers.

One potential (but minor) issue I see is that on a typical vcxo, the control signal is a low-power signal. Here, it needs to be a power signal - being able to supply 10-20ma minimum.

That can be cured, however, with a emitter follower or even a regulator.
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Offline JoeN

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #64 on: April 08, 2015, 03:17:00 am »
Following this thread I built myself an oscillator, actually four so far, that work well out of 7404, 74LS04, 74LS14, and 74HC04 ICs (they all run 19-22Mhz except the Schmitt trigger one which runs more like 12Mhz).  I took the advice of the person who told me I should be the person to test out an ECL circuit and I am going to attempt to build that too, but I don't know anything about ECL so I think I will ask for some advice here.  I don't have an ECL inverter but I do have the part MC100EP105 (http://www.onsemi.com/pub_link/Collateral/MC10EP105-D.PDF) which is AND/NAND and can be made into an inverter by feeding the output of one stage into both the inputs (one differential pair to two differential pairs) of the next stage.  So this is the plan:

I0->I1 (first "inverter" to second)

Q0 ->!D1a 29->22
Q0 ->!D1b 29->20
!Q0->D1a 30->23
!Q0->D1b 30->21

so, pin 29 to pins 20 and 22, pin 30 to pins 21 and 23

I1->I3 (second "inverter" to third)

Q1 ->!D3a 2->14
Q1 ->!D3b 2->11
!Q1->D3a 3->15
!Q1->D3b 3->12

so, pin 2 to pins 11 and 14, pin 3 to pins 21 and 23

I3->I0 (third "inverter" back to first)

Q3 ->!D0a 6->26
Q3 ->!D0b 6->24
!Q3->D0a 7->27
!Q3->D0b 7->25

so, pin 6 to pins 24 and 26, pin 7 to pins 25 and 27

And a tap off of D0a as the oscillator output.  Vcc = +5V, Vee = 0V

I have to use an adapter board and traces are probably longer than they should be.  For traces above I will cut the wires to the same length to equalize propagation delays regardless of if they need that length or not.  Unfortunately, the adapter board itself has varying lengths on the traces.

Is it that simple or am I being naive about ECL circuits?  Thanks.

« Last Edit: April 08, 2015, 03:21:14 am by JoeN »
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Offline T3sl4co1l

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #65 on: April 08, 2015, 03:31:16 am »
If you have any kind of trace length (i.e., comparable to the rise time -- 100ps is only 2cm of trace or coax), you will need termination resistors.  And I forget, but suspect, that ECL needs/wants a termination resistor for correct bias anyway.  Follow the datasheet instruction with termination resistors and terminating voltage: bypass the termination resistor to ground as short as possible, using chip resistors/capacitors and ground plane.  The termination supply can be generated with an op-amp or something like that; it should be capable of bidirectional current flow (so, don't just use an LM317 or something).  Be sure it can handle plenty of current.

Likewise, your maximum frequency will be limited by propagation delay of the gates as well as the interconnects.  Should still be around a GHz though!

Tim
« Last Edit: April 08, 2015, 03:33:00 am by T3sl4co1l »
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Offline hamster_nz

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #66 on: April 08, 2015, 03:35:18 am »
I have to use an adapter board and traces are probably longer than they should be.  For traces above I will cut the wires to the same length to equalize propagation delays regardless of if they need that length or not.  Unfortunately, the adapter board itself has varying lengths on the traces.

Is it that simple or am I being naive about ECL circuits?  Thanks.

If you want to have a fun read about some interesting uses of ECL logic, have a look at the internals of a early Cray http://american.cs.ucdavis.edu/academic/readings/papers/CRAY-technology.pdf - full of interesting detailed stuff like:

Quote
With signal rise times (10 percent-90 percent) of 750 ps,
open line stub lengths must be less than 0.5 in to hold reflections
under 35 percent overshoot and under 12 percent
undershoot. Larger reflections can saturate gate inputs and
reduce noice immunity. Longer signal runs must use transmission
lines terminated in the line characteristic impedance.
The CRAY-1 boards have 7-mil wide lines and 7-mil spaces.
The 7-mil height above a ground (or power) plane results in
a 60-52 microstrip line with a delay of 0.15 ns/in.
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Offline JoeN

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #67 on: April 08, 2015, 03:43:48 am »
If you have any kind of trace length (i.e., comparable to the rise time -- 100ps is only 2cm of trace or coax), you will need termination resistors.  And I forget, but suspect, that ECL needs/wants a termination resistor for correct bias anyway.  Follow the datasheet instruction with termination resistors and terminating voltage: bypass the termination resistor to ground as short as possible, using chip resistors/capacitors and ground plane.  The termination supply can be generated with an op-amp or something like that; it should be capable of bidirectional current flow (so, don't just use an LM317 or something).  Be sure it can handle plenty of current.

Likewise, your maximum frequency will be limited by propagation delay of the gates as well as the interconnects.  Should still be around a GHz though!

Tim

Ha, this is what I was thinking the issue was.  I am going to have to have a small PCB made to try this out.  Good thing boards are only $5 a square inch these days for three.  Not only is there really no way to breadboard this circuit, it sounds like it would be next to impossible even with solder on a perfboard using a QFP-32 adapter, which is what I was thinking of doing.
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Offline T3sl4co1l

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #68 on: April 08, 2015, 03:50:30 am »
A QFP adapter, maybe not; but building it up on copper clad wouldn't be impossible.  Just tedious.

If you have shaky hands, hand-carving a board is probably beyond your scope, but if not, 0.05" pitch traces are easy to create with a utility knife.  Vias are probably harder (you need to poke a hole and solder or rivet in something conductive!).

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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #69 on: April 09, 2015, 01:12:59 am »
Following this thread I built myself an oscillator, actually four so far, that work well out of 7404, 74LS04, 74LS14, and 74HC04 ICs (they all run 19-22Mhz except the Schmitt trigger one which runs more like 12Mhz).  I took the advice of the person who told me I should be the person to test out an ECL circuit and I am going to attempt to build that too, but I don't know anything about ECL so I think I will ask for some advice here. 

Sounds good!  Looking forward to seeing what you come up with.   


Added a little more insulation to my chip cooler. 
« Last Edit: April 09, 2015, 01:20:42 am by joeqsmith »
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #70 on: April 09, 2015, 01:19:35 am »
Ran the voltage sweeps for the four new parts.  See attached.     The Motorola MC74AC14N is the second fastest part I tried at about half the speed of the F.     Wanted to see what the edge rates on this thing look like.   Pretty good. 

Changed cables to allow me to use the DSOs with the cooler.   
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Offline dannyf

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #71 on: April 09, 2015, 01:26:17 am »
it doesn't have to be a ring (3x gates). One gate works just fine - connect its input to its output.
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #72 on: April 09, 2015, 01:45:04 am »
it doesn't have to be a ring (3x gates). One gate works just fine - connect its input to its output.



I think people understand that.  If you looked at the LVDS oscillator I showed, that was one gate. 

Cooling the Motorola part to -10C slightly improved the fall times and frequency.   
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Offline joeqsmith

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #73 on: April 09, 2015, 03:50:29 am »
Going back and looking at the low voltage operation, the Motorola MC74HC04N won out.   I ran the part at 22, -5 and 50C.  Part runs at a slightly lower voltage at higher temperature.   0.846 volts is about it with sub KHz output. 
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Offline JoeN

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Re: Waveforms in a 74LS04 ring oscillator.
« Reply #74 on: April 09, 2015, 06:21:56 am »
If you have any kind of trace length (i.e., comparable to the rise time -- 100ps is only 2cm of trace or coax), you will need termination resistors.  And I forget, but suspect, that ECL needs/wants a termination resistor for correct bias anyway.  Follow the datasheet instruction with termination resistors and terminating voltage: bypass the termination resistor to ground as short as possible, using chip resistors/capacitors and ground plane.  The termination supply can be generated with an op-amp or something like that; it should be capable of bidirectional current flow (so, don't just use an LM317 or something).  Be sure it can handle plenty of current.

Likewise, your maximum frequency will be limited by propagation delay of the gates as well as the interconnects.  Should still be around a GHz though!

Tim

OK, here is my schematic and on the PCB I try to keep the traces about equal length and the resistors very close to the pins they are terminating.  Am I even close to being right on this?  I read the ON guide to termination as well as one from Micrel and as far as I can see this seems to be the way it is done.  One guide seems to say that you don't need bypass caps for ECL because it is inherently balanced but I included two anyway.  Device is MC100EP105.  Resistors and caps are 0805.  Resistor is metal film 1%, caps are ceramic.  The output is an SMA edge connector.  Any idea about what I should do for unused inputs and outputs on the unused gate?

« Last Edit: April 09, 2015, 06:24:03 am by JoeN »
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