DMTD board

[chuckb]

I just learned Mini-circuits will sell insulated spacers for SBL-1.  I am requesting price quote and will update this post once I get it.

P/N B14-045-01

I got a quote.  40 cents each.

Were you able to get those spacers?
Otherwise Mouser has spacers for a single pin - 144-R902-1 that work fine, 2 per mixer,  $0.21 ea.

My board is going together now.

[tkamiya]

Yes, I received them yesterday.  It ended up being a rather expensive purchase.  Shipping was $10!

[cncjerry]

If it's interesting for someone: I made some progress with the layout of my quad mixer. In the picture attached is one half. They are almost perfectly symmetrical, I even tried to match the trace lengths between the channels.
I never did a PCB layout with ECL gates before, and I have been warned it will be "extremely difficult", but I don't know to what degree this is true. Therefore I took care to minimise every track's length which has to do with the ECL gates.

The absolute delay between the channels is not all that important, as long as it is constant.

I just proved this to myself after working for several days to try to figure out why I have a phase shift between the two identical channels of a DMTD.  I averaged the output and subtracted that from the the result channel and plotted it. ADEV was Identical, of course.  I still cant figure out why I have a phase shift before the ZCD in Riley's circuit...  something to do with grounding or lack thereof.

I would shy away from a complex filter or a complex  ZCD as Riley jn subsequent emails had made it clear to me that noise reduction is where you should spend your time.  One thing you might want to try is Rick Campbell's diplexor for mixer termination, used in DC receivers.  But I think you would have to have a 50ohm path from the input through the mixer. The DMTD channels are just DC downconverters.

Also, I suggest you use one reference no matter how many channels with a passive splitter combiner.

Lastly, the old PICTIC works great with this system and can be built cheaply from Riley's paper if you don't have a TIC.  Riley used one for his excellent results.

Jerry

[5065AGuru]

We are working on an INEXPENSIVE and SIMPLE companion counter for the simple dual mixer so I'd not spend any $$ now for a PITIC unless you want it for other uses.
Hope to be able to share in the near future as it's looking really nice!

Cheers,

Corby

[thinkfat]

I have a TAPR TICC, I'm going to use that. I think I can do a three-cornered hat between the two channels and the reference input of the TICC, no?

[notfaded1]

I have a TAPR TICC, I'm going to use that. I think I can do a three-cornered hat between the two channels and the reference input of the TICC, no?

Wouldn't you need two TIC's to do a 3 cornered hat measurement?  I think they have paper on linking multiple TAPR TICC's together for doing this kind of thing?  If you want to do a hack and use the B-A channel to create a fake channel C you could kinda fake a 3 cornered hat measurement but it's not the same as having three separate real time stamped channels:

https://lists.febo.com/pipermail/time-nuts_lists.febo.com/2016-November/084591.html

I found the application note about Mutiple TAPR TICC's and attached it.

Bill

[Mrt12]

Dear colleagues
so I finished my Quad Mixer design or dual DMTD. See the attached PCB layout. It is all SMD. Also I decided to use two cascaded OpAmp stages. For first tests, the 2nd one can be omitted. A LM311 is used as comparator.
I will make a very simple time-stamping counter on a separate PCB.
What do you think of my layout?

N10 in the middle is a +/-15V voltage regulator and besides the SMA connectors the only THT component.

[tkamiya]

I'm wondering....  since the layout is so dense, perhaps some kind of guarding, shielding, or maybe just space would be a good idea? 

Also use of DC/DC converter....  I presume 15V is chosen to drive the opamp.  Wouldn't typical 100mV P-P noise/ripple affect detecting the true zero-cross point?   -  never mind!  I see filtering.

[cncjerry]

We are working on an INEXPENSIVE and SIMPLE companion counter for the simple dual mixer so I'd not spend any $$ now for a PITIC unless you want it for other uses.
Hope to be able to share in the near future as it's looking really nice!

Cheers,

Corby

Based on the TDC7200?  I've ben considering building another TICC dead-bug style as there are only 10 chips on that shield and a couple are level converters.

[notfaded1]

We are working on an INEXPENSIVE and SIMPLE companion counter for the simple dual mixer so I'd not spend any $$ now for a PITIC unless you want it for other uses.
Hope to be able to share in the near future as it's looking really nice!

Cheers,

Corby

Based on the TDC7200?  I've ben considering building another TICC dead-bug style as there are only 10 chips on that shield and a couple are level converters.

I'd wait to see what Corby and Tom come up with.  From what I've been hearing it's going to be pretty legit.  I can't think of anyone here that would know better either.  They both have some of the best references and measurement gear I know.   

Bill

[ch_scr]

Here is my dogmeat "DMTD". Turns out the LM160 (or at least my Tesla MAC160) definitely have a temperature dependant delay.
My time interval reading is drifting around slowly, and I can make it drift (more) if I put my finger on the case of one MAC160.
If I take the finger away, it drifts back. Guess that's whats meant by "temperature compensated" in the ECL buffer datasheets?
Edit: Found an app note that has a relevant graph. Pretty amazing how sensitive this is.

[Mrt12]

I'm wondering....  since the layout is so dense, perhaps some kind of guarding, shielding, or maybe just space would be a good idea? 

Also use of DC/DC converter....  I presume 15V is chosen to drive the opamp.  Wouldn't typical 100mV P-P noise/ripple affect detecting the true zero-cross point?   -  never mind!  I see filtering.

The DC/DC converter operates at around 500kHz, so its frequency is anyways way beyond the bandwidth of the amplifiers. But you are right, I inserted some DC filters.

Concerning the shielding of components - you are right as well, this is the only part where I am a bit worried. On the other hand, the ECL gates have differential outputs, so I don't see that they should cause EMI problems.
By the way I plan to make this as a 4layer board which means I do have a solid ground and 5V plane.

We are working on an INEXPENSIVE and SIMPLE companion counter for the simple dual mixer so I'd not spend any $$ now for a PITIC unless you want it for other uses.
Hope to be able to share in the near future as it's looking really nice!

Cheers,

Corby

Based on the TDC7200?  I've ben considering building another TICC dead-bug style as there are only 10 chips on that shield and a couple are level converters.

The TDC7200 is very good. However I think it is not necessary for a DMTD. 10ns or even 100ns resolution should be good enough; realistically, with the TDC7200, you get 1ns. Perhaps 500ps. I am unsure whether this improvement is so dramatic that it justifies the additional costs and complexity, does it?

[thinkfat]

Dear colleagues
so I finished my Quad Mixer design or dual DMTD. See the attached PCB layout. It is all SMD. Also I decided to use two cascaded OpAmp stages. For first tests, the 2nd one can be omitted. A LM311 is used as comparator.
I will make a very simple time-stamping counter on a separate PCB.
What do you think of my layout?

N10 in the middle is a +/-15V voltage regulator and besides the SMA connectors the only THT component.

If I'm not mistaken, the MC100EL16 is 8V abs max between Vcc and Vee. You'll release magic smoke if you supply it from the +15V rail.

[Mrt12]

Dear colleagues
so I finished my Quad Mixer design or dual DMTD. See the attached PCB layout. It is all SMD. Also I decided to use two cascaded OpAmp stages. For first tests, the 2nd one can be omitted. A LM311 is used as comparator.
I will make a very simple time-stamping counter on a separate PCB.
What do you think of my layout?

N10 in the middle is a +/-15V voltage regulator and besides the SMA connectors the only THT component.

If I'm not mistaken, the MC100EL16 is 8V abs max between Vcc and Vee. You'll release magic smoke if you supply it from the +15V rail.

don't worry, there is also a 5V input ;-)

[cncjerry]

You might find this helpful if using TimeLab.

There is a section titled 'Masks" and I use it to evaluate my boards vs known baselines.  This isn't meant to evaluate one board vs another because the method used to acquire the data might be different for each boards.  Also, these work with 'ADEV' plots with the prefix on the line of 'a'.  If you have other measurement  baseline data like 'p' or 'm' you can add that as well (with the appropriate line prefix character).  I think you will find it interesting to look at Corby's Mask vs some of the other much more expensive options just by turning them on, up to three at once.

I added Corby's mask from the data he published on the first page, I think it was.  If it has been updated, then the pairs below of (tau, value) would need to be corrected.

I also added Riley's baseline.

Add these statements to your "masks.txt" file by going to Masks, edit mask definitions.  The separator commands do just that; organize these within the drop-down list with a separator line.

Code: [Select]

separator

mask Riley DMTD baseline
a (0.1, 5.24e-13) (0.2, 2.73e-13) (0.4, 1.34e-13) (1.0, 5.43e-14) (2.0, 2.74e-14) (4.0, 1.4e-14) (10.0, 5.71e-15) (20, 2.93e-15) (40, 1.44e-15) (100, 5.91e-16) (200, 3.03e-16) (400, 1.57e-16)

mask Corby DMTD baseline
a (1, 2.46e-13) (2, 1.34e-13) (4, 7.97e-14) (8, 4.51e-14) (16, 2.15e-14) (32, 1.07e-14) (64, 5.66e-15) (128, 3.1e-15) (256, 1.62e-15) (512, 7.26e-16) (1024, 3.73e-16) (2048, 3.63e-16)

separator


I put them right after this line:

Code: [Select]


mask Kvarz CH1-76A passive maser (5 MHz typical)
a (1, 4.8E-13) (10, 1.5E-13) (100, 4.5E-14) (1000, 1.5E-14) (3600, 8.5E-15) (86400, 4E-15)
P (10, -110) (100, -125) (1000, -150) (10000, -150)


Jerry

[cncjerry]

The tdc7200 chips and associated circuitry, if operated on 3.3V, cost almost nothing and on 5v you had to add level converters that add complexity in board design and soldering.  A guy I am working with replaced the TIC on the front-end of Lars GFPSDO with one and it was a relatively simple change.  The TAPR TICC, that a lot of people have including me, uses two, one for each channel with 11 digits of resolution, no carefully selected components or special caps, etc.  Only issue is that you must have logic to account the overflows over what, 800ns I think it is, in the specific mode.

From what I found, the biggest problem with the DMTD system is 60/120/180hz ground loop problems and noise.  For instance, I ran a baseline and it was so close to Riley's baseline you can't really see the difference on the plot. I ran this over and over without an issue.  Then I made some changes as I readied to test a GPSDO and now I can't get back there.  I can watch it snap back and forth so clearly either something is failing on the board or a grounding problem has shown-up that eludes me.  So yes, if it took that much longer to implement a tdc7200 TIC vs improving the grounding, coupling, etc., then you would be better off doing that, I guess.

I have to build mine into a box.  The intermodulation of local FM stations can be seen in subharmonics in my case, all over it.  Riley mentions about aliasing in his notes, so yes, you get a lot of accuracy for the money, almost can't be beat, check the masks I created vs much, much more expensive products, but I don't think you can get there just throwing it together on a couple of boards without shielding and careful attention to grounding.  I'm not suggesting anyone would try except for me!

I've worked on DMTD, loose and tight PLL, etc  so long I forgot why I even started.  I think I wanted to update the oscillators in my Lucent GPSDOs and possibly the one in my Cs beam and then couple one to clean-up an Rb unit.

Jerry

[tkamiya]

Corby,

Would you mind giving a newbie a giant favor?  I am done with populating the board except for SMD parts.  Power supply is already done and tested.  1Hz offset signal is ready.  By tomorrow, I will be able to conduct initial functional test.  What kind of wave form should I be seeing on output?  I would imagine nearly 1Hz pulse or square wave, but an actual oscilloscope screenshot will be very helpful.

Like you, I ended up soldering one of DBM backwards.  In process of pulling it out, I damaged the through-hole.  I used the thin wire trick to repair it but I want to make sure it is actually functioning.  The colored pin at bottom is supposed to line up with square copper foil, correct/ 

Just to make sure....on LM311, both in 5 and 6 has connected pads.  Yet, there is nothing on schematic.  What are these for?  Datasheet shows they are for zero adjust.

I'm impressed how you crammed parts in this little board!

[thinkfat]

Corby,

Would you mind giving a newbie a giant favor?  I am done with populating the board except for SMD parts.  Power supply is already done and tested.  1Hz offset signal is ready.  By tomorrow, I will be able to conduct initial functional test.  What kind of wave form should I be seeing on output?  I would imagine nearly 1Hz pulse or square wave, but an actual oscilloscope screenshot will be very helpful.

You should see a 1Hz square wave with 50% duty cycle on the outputs.

[tkamiya]

Ladies and gentlemen! 

My Corby2020 system is doing SOMETHING!  I am getting square waves at both channels.  I will need to properly wire this before going any further but functionality is definitely there.  Yay 

[5065AGuru]

Taka,

Glad you got it built!

Yes the colored pin goes towards the foil square.

On all mine that meant that the "writing" between the tops of the mixers were pointed opposite.

If you use a T to connect both inputs together you should see the 1Hz outputs in phase.
(Both should be high or low at the same time.)

Those pads were in case I used a different comparator. Leave unconnected for the LM311.

Look over the tutorial post for some info on making measurements.

I'd just hook up two oscillators, adjust one of them to make the counts increment slowly and log some data.

With PLOTTER you then open the file just made.

With TimeLab you can do that also but I think there is a mode that takes data in real-time and you can watch the AD develop directly.

Cheers,

Corby

[tkamiya]

Corby,

I also noticed there is an extra output for each of the ports.  No connectors.  Just pads on PCB.  I'm assuming they are there just in case someone wanted an LED or hook up a scope.  Is that right?

[notfaded1]

Ladies and gentlemen! 

My Corby2020 system is doing SOMETHING!  I am getting square waves at both channels.  I will need to properly wire this before going any further but functionality is definitely there.  Yay 

Congrats Taka!!!  That looks like a nice setup.  What case did you put that in?  It looks a little like the one Corby made first.  I'm trying to figure out the long term power supplies for this still.  We need all these different DC voltages and I'm wondering what's really the best way to go about it?  Is there an elegant way to do it with linear PS somehow vs. multiple linear PS's?  Or even some switching I suppose but I've always been kinda adverse to them despite the size and such when dealing with sub ppm measurement applications???

I picked up some 1050A's last night.  They all have the 015 option for disciplining the OCXO.  I'm hoping they'll go hand in hand with the DMTD.  I'm not sure how it work when using the PLL to sync the quartz?  Do they keep the sync after you disconnect the ext. input?  Seems for great S, M, L term stability using a Cesium to sync to the quartz then running off the quartz is the way to go.  Also I'd be interested to see if I can improve on the 5065 output by trying the same thing.  The 5065 has a really good LO but perhaps a well aged 1050A might give it an edge?  Anyhow there's only one way to find out right and I can't think of a better way to check than with this DMTD from Corby.  I don't have the Efratom DMTD documentation but judging from what Corby said it sounds like this design is very similar to it.

Bill

[tkamiya]

Here's my power supply.  After this, there are four 3 terminal regulators.  Transformer puts out 8V per winding.  I just used what I already had....

Case is a shallow 2U aluminum case I bought on eBay.  I can't find a link for it now.  6 panels bolts together.

[Mrt12]

Dear colleagues
today I received my ECL gates: a couple MC100EL16 and MC100EL11. Found them for a good price on eBay.
I immediately wanted to test the gates and see how they perform when fed with a sine wave. So I soldered a couple of them in an ugly dead-bug style to a piece of PCB, attached a Thevenin termination network and a couple SMA connectors.
I measured the output waveforms (Q and Qbar) with the scope with different input frequencies and amplitudes. For the high frequencies, the oscilloscope pictures are not so accurate as my scope's bandwidth is only 1.5GHz. However we can see that the output amplitude stays nicely constant over a wide frequency range.
Further, I also varied the input power. From about -20 to +7dBm, the output waveforms look the same. If the input power is increased above +8dBm, the output waveforms become more and more distorted, and below -20dBm the output amplitude stays more or less constant but the waveform becomes more sine-like.
I also measured the reverse isolation using an HP 8753C network analyzer. Up to 1GHz, the isolation with my crappy soldered test circuit is, according to my measurements, approx. 80dB. I am not sure whether this is acceptable, but I assume it is as most oscillators which we are going to test already have some sort of output amplifier included. For example, my GPSDO has already an OpAmp based buffer amplifier built in, which has a reverse isolation of around 50dB, so the total reverse isolation when the GPSDO is connected to an MC100EL16 is around 130dB, which should be good enough for most measurements.

The output power of the MC100EL16 is around 1dBm (circa 700mV). This is a bit less than specified in the datasheet, but acceptable I'd say for the ADE-1+ mixer, isn't it?

I am thinking about whether I sould use a MC100EL11 for the offset oscillator, as the '11 has two outputs. However I am not sure how well they are isolated from each other and I have only 6 of those ICs, so I don't want to waste too many of them...

But I think from these measurements we can say that the MC100EL16 is an acceptable alternative to the MC1650 and is still available these days. Even at mouser for a decent price.
So I think I am going to finish my PCB and we'll see how it works :-)

[thinkfat]

Can you add a small resistor into the +5V rail and measure the current draw? I've read somewhere that ECL gates are somewhat "quiet" regarding their current draw, unlike high-speed CMOS gates.