DMTD board

[tkamiya]

I'm going to make one as a direct copy of Corby's design, then have another where I will experiment.  As to if DBMs are symmetric, they look that way.  I've taken few apart. 

I've made my power supply with linear regulators.  I wasn't comfortable with ripples and noise in involving switching power supply.  At minimum, if I have to do that, I'll do that on another PCB and well filter it.  It didn't make sense to me to get those expensive low noise OPAmps and use dirty power supplies.  It'll be interesting to see what difference, if any, substitution will make though.

[Mrt12]

I just had a thought for the 5MHz Reference I could use the BVA.  I'd like to figure out a 5MHz and 10MHz setup.  Another question.  If you had two of these setup could you hook it up so you could do three corner hat measurements?  Would you use the same reference or same offset reference in a case like this?  Obviously I'd like to start with one that works but thinking about how you would hook up for three corner hat measurements?  I'm going to learn the other software you're using Corby.  I've used Stable32 and timelab.  I'm not as familiar with your other tool.

Regards,

Bill

Hi Bill
I am also working on a DMTD for a while now. It is actually not a DMTD but a TMTD, a "triple mixer". It uses exactly the approach you mentioned.
There are four inputs: three inputs for the DUTs, and one for the offset oscillator. The zero crossings are then time-stamped and via the appropriate data processing you can do three cornered hat. That is exactly my plan.
I was almost finished with my design when I saw this thread and noticed Corby's excellent idea of using an ECL gate to drive the mixers. That's a brilliant idea because it will make the whole thing less sensitive to the input signal level.
Also I hope that the ECL gates provide a certain degree of isolation.
I ordered a couple MC100EL16 because the MC1650 Corby uses is obsolete and no longer available. The MC100EL16 is a driver, but it can be AC coupled from a sine wave. That's what I plan to do. With some of the ordered devices I want to test first how well that works and what degree of reverse isolation they provide. Next step is then to add them to my design.
However my design is on a 130x80mm PCB and uses SMT components only. For the mixers, I plan to take ADE-1+ or ADE-2+ which will work up to 400MHz or 1GHz, respectively. For me, the high frequency end is almost as important as 10 MHz because I want to characterise 100+ MHz oscillators as well.

[tkamiya]

I haven't done multi-channel DMTD personally but here's a note from someone who has:

https://ftp.tapr.org/tech_docs/multi-TICC_App_Note_2020-01.pdf

When you go there, you might get a warning from your browser.  TAPR is a known ham radio organization.  It's safe.  TICC is a time interval counter.  I have one. 

[notfaded1]

That would be the ultimate right multiple port DMTD with linked TIC's counting together aka poor mans PhaseStation 53100A.

[thinkfat]

I have made a layout for the board. It's intended for either powering from µPowerDirect A324R (3W) or Traco TEN4-2422 (4W), whichever makes the cut
(you guessed it, parts bin had both. 3W might be on the edge tho).
It's intended to be milled as 2-sided PCB, the yellow inner layer shows placement of wire links. This is done so a groundplane can be on one side.
I have 4 seperate local regulation +-6V for both inputs (1,2) the offset input (3) and both IF amps (4) with LM337 / LM317 SO-8.
I suppose this is more usefull as a starting point then to be made as a direct copy.

Is there an inherent advantage in using a differential IF configuration? I figured my parts bin doesn't contain any Tesla stuff but instead of the MA3000, any FDA could be used, like, LTC6362 or THS4131?

The THS4131 could be used with a single 5V supply rail, at the cost of increased THD (haha!).

[5065AGuru]

Taka,

See the PIX showing the SMD on the bottom. That post also has the parts values!

Yes the mixers need to up off the board a tiny bit!

Of course you want one of your best performers for the REF input.

You can test a few 10811 against each other and isolate the best ones.

As good as or better is fine, it would be very hard to find a REF that is 10X better than most of what we see!

I use my HP5065A for almost all measurements, and only switch to my FTS1200 when I'm most concerned about the lower Tau. (about8 Sec and below.)

Cheers,

Corby

[5065AGuru]

Bill,

I'd recommend using TimeLab.
I'm just using PLOTTER in my examples as I use it all the time!
Plotter does not like the commas the 53131A puts out but TimeLab works fine with them.
Also TimeLab has more versatile measurements and plots.

Once we get the custom counter debugged you will not have to tie up a fancy instrument and can just build it into the same box your dual mixer is in!

Cheers,

Corby

[tkamiya]

You can test a few 10811 against each other and isolate the best ones.

And, THIS puts me squarely back to my original problem.  I'm in a position where none is proven to be better than the rest.  There are lots of candidates but not one has been selected.  Given that, how can I accomplish this goal?  DMTD as well as all other measuring method requires one to compare DUT against other to choose the best - which requires one unit that is far better than the rest.  I can compare 11801 against another 11801 but I can't imagine how useful this will be....  as in the end, I will not know if i just measured DUT or the reference.  Or, am I missing something?

[FriedLogic]

Nice work, I haven't had a chance to read thru it all yet.  I just built Bill Riley's dual mixer setup using one of Bert's boards and it works great.  Wondering if there was a reason why you didn't use transformers on the input side?

   I see isolating transformers being used in quite a few projects, but I'm not convinced that it is usually the way to go for best performance.
   I've noticed that isolating transformers can make noise issues worse, and have usually had better results with good solid grounding.
   I expect that there are situations where a DMTD might benefit from them, but in most cases I don't see an advantage. Although not as neat or cheap, they can always be added externally if necessary.

   Some versions will no doubt be done with isolating transformers, so it will be interesting to see the results.

[5065AGuru]

Taka,

You can use a DMTD system to figure out your best oscillator!
Traditionally when you build an ultra-stable oscillator and want to evaluate it you build two.
Then you test them against each other.
You do NOT need one to be MUCH more stable than the other!
I don't remember the exact math but if I remember correctly two identical stability oscillators will give an Allan deviation that needs to be degraded? by 1.4. So if your two oscillator read 5X10-13th then they really are 1.4X5 or 7X10-13th. I may have the maths wrong but if you research DMTD enough there are references to it.
Maybe someone can weigh in on this.

Also three corner measurements can help you measure the real performance.

For my standards I can't really tell if an oscillator is better that around 2.5X10-13th at 1 Second although I can accurately measure down to 7X10-14th at 100Sec.

Cheers,

Corby

[tkamiya]

Right.  But how you tell which is which?

Say I have OSC1 and OSC2.  OSC1 into DUT port, OSC2 into REF port.  DMTD will output the time between a pulse from OSC1 and next pulse from OSC2.  One output per cycle.  How do you tell which one is better?  I can understand it will give aggregate of both - say both are at some degraded number from actual reading.  But my need is to compare.  Keep comparing until one remains as a winner.  How can THAT be done?  I have more than a dozen 11801 ready for this process.

This has been a problem since beginning.  I was getting ready to buy a brand new OCXO so I can trust the factory data.  But 11801 are incredibly good.  To one up on it, I'll have to spend quite a bit.  Can I come over to your house post-Covid with stacks of sandwiches?  Will you let me measure against your Rubidium?

[5065AGuru]

Taka,

Just test them pairwise against each other.

As you fine pairs that test better than others keep going until a couple clear winners are found.

If you have HP 5065A, 5061A, 5061B, or 105B that have the 10811-60109 then use those instruments outputs (in open loop) at first.

Most 10811-60109 give a performance of between 4 and 7X10-13th in the low Tau region.

They are the best version out there. The ones in the 5071A can also be good.
I do however have a 10811-60111 that also gives that level of performance but that is rare!

The 5065A (locked) usually has an AD of between 1 and 2X10-13 at 100Sec so could be used to start picking out the best out the pile of oscillators!

Everyone has there "golden" or favorite oscillator but it's a never ending search!

Cheers,

Corby

[tkamiya]

Corby,

How about something like this.  Say I will build and set up two complete DMTD system.  They will share difference ref.  Take a reference oscillator and divide that signal into 2.  Each of the leg goes to ref port of DMTD1 and DMTD2.  DUT will have OSC1 and OSC2.  Take Adev measurement on both simultaneously.  Then, I will be able to pick which one is better relative to each other, although actual reading will be irrelevant.  I can keep going like this 2 OSC at a time.  Then gather better of two as a set.  Now, repeat the process until one is a winner.  I should, actually, have enough parts to make 3 complete set.

Now, take 2 of the best.  Place the best one as common REF and test original REF and the second best.  After this step, I can tell if REF is any good....

[chuckb]

With the Three Cornered Hat technique, you measure the three pairs of oscillators, A-B, B-C, C-A, develop the AD curves for the pairs, put that data into the TCH algorithm and it will provide the unique curves for A, B and C. The Stable32 software will do all of this for you. I don't know about other software packages.

I used the technique a month ago and it worked well.

I got my Corby DMTD PCBs today. I'm still waiting on a few parts from China. I have two nice Datum / FTS 1130 10MHz osc that I want to test. They were pulled from some Telecom freq references. I have not found any data on these but they are in the same package as the high end Datum 1000 osc.

The Datum crystal osc will probably be my best reference up to 100-1000 sec. Then the GPS locked Rb standard will be best for more than 1000 sec.

[edpalmer42]

I have two nice Datum / FTS 1130 10MHz osc that I want to test. They were pulled from some Telecom freq references. I have not found any data on these but they are in the same package as the high end Datum 1000 osc.

I found a small note on the FTS 1130.  Looks very nice!

A Stratum Three module uses an AT-cut FTS 2510
OCXO as the oscillator. The Stratum 2.1 module uses
a SC-cut FTS 1000B oscillator. Its performance greatly
exceeds the Stratum 3 module, but falls short of the
Stratum Two requirements for thermal stability. The
Stratum Two module uses an FTS 1130 oscillator. The
1130 oscillator utilizes a double oven technique to
provide the required thermal stability. The inner oven
is hermetically sealed to provide immunity to humidity
changes [5]. Table 3 lists the specifications for the
different oscillator modules.

Table 3. Oscillator Module Specifications
                                            Str 3      Sir 2.1         Sir 2
Tuning Range                        10e-6     3e-7            3e-7
Thermal stability(per ' C)         7e-9       1.7e-11       3e-12
Aging (per day)                      1e-8       1e-10          5e-11
Time constant range(secs)     20-100    100-3,000   100-10,000

https://archive.org/download/DTIC_ADA272017/DTIC_ADA272017.pdf

[ch_scr]

Is there an inherent advantage in using a differential IF configuration? I figured my parts bin doesn't contain any Tesla stuff but instead of the MA3000, any FDA could be used, like, LTC6362 or THS4131?

The THS4131 could be used with a single 5V supply rail, at the cost of increased THD (haha!).

MA3000 is clone of RCA CA3000. But there are still companys around that have stock of MA3000. In principle any FDA could be used.
The FDA should amplify a slow changing voltage (1-10Hz) -> low input offset voltage, input offset voltage thermal drift and voltage noise
It should attenuate residual high frequency signal coming through filter -> high CMRR at Frequency in 10Mhz range.

Differential signal path has the benefit of not beeing referenced to ground (currents through the groundplane can't inject noise).
When using a single ended topology you have to make sure all components (opamp inputs, filter components) see the "same" ground -
for MHz you want a groundplane, for Hz you want star ground (generally speaking). Here you have both so it might be complicated.

I have opted to just reference all the circuit to the groundplane, in a single ended configuration this would not be optimal.
In my circuit the only (DC) connection of the IF signal to ground is at one point, and not directly as something to compare against as well (opamp/comperator input).
Also, if noise couples into the differential path from the outside (hopefully evenly) it is rejected by the opamp (to the best (CMRR) of it's ability (inside it's bandwith))

[thinkfat]

I've been experimenting a bit, simulating the design in LTSpice. I've added the current schematic as an attachment.
I like the idea of using the MC10EL16 as input buffer, though it seems a bit tricky to terminate ECL gates properly (schematic also attached).

All the FDAs I found have a Vocm voltage output, which you can use to set the center threshold for a comparator or DAC.
The output of the mixer is floating, isn't it? It's not ground referenced. Does it make sense to loosely bias it to Vocm (R14/R15 in my schematic) to prevent the differential pair from drifting outside of the valid input range? Or are the amplifier inputs always biased against the Vocm anyway?

I as far as components go, I just used what seemed appropriate in the LTspice library. As far as I can see, this design could be run from a single 5V supply rail (or multiple 5V rails).

[Mrt12]

I've been experimenting a bit, simulating the design in LTSpice. I've added the current schematic as an attachment.
I like the idea of using the MC10EL16 as input buffer, though it seems a bit tricky to terminate ECL gates properly (schematic also attached).

All the FDAs I found have a Vocm voltage output, which you can use to set the center threshold for a comparator or DAC.
The output of the mixer is floating, isn't it? It's not ground referenced. Does it make sense to loosely bias it to Vocm (R14/R15 in my schematic) to prevent the differential pair from drifting outside of the valid input range? Or are the amplifier inputs always biased against the Vocm anyway?

I as far as components go, I just used what seemed appropriate in the LTspice library. As far as I can see, this design could be run from a single 5V supply rail (or multiple 5V rails).

Yes the MC10EL16 has the advantage that it is still in production and is available in SMT packages. We could even think about using the MC100EP16VA: this is basically the same, but with a higher gain. This would allow for an even larger dynamic range at the input!

As for the termination of the ECL gates, I read the corresponding application notes from ON Semi. I first went for the Y Termination in my design, the same as you do. However I am unsure; maybe the Thevenin termination is better because the voltage ad the Q and Qbar pins is better defined. Also it is only one additional resistor compared to the Y termination, so the disadvantage is not a big deal I think.

I am still a bit concerned about the DC coupling between the ECL gate and the mixer, though.

[thinkfat]

I've been experimenting a bit, simulating the design in LTSpice. I've added the current schematic as an attachment.
I like the idea of using the MC10EL16 as input buffer, though it seems a bit tricky to terminate ECL gates properly (schematic also attached).

All the FDAs I found have a Vocm voltage output, which you can use to set the center threshold for a comparator or DAC.
The output of the mixer is floating, isn't it? It's not ground referenced. Does it make sense to loosely bias it to Vocm (R14/R15 in my schematic) to prevent the differential pair from drifting outside of the valid input range? Or are the amplifier inputs always biased against the Vocm anyway?

I as far as components go, I just used what seemed appropriate in the LTspice library. As far as I can see, this design could be run from a single 5V supply rail (or multiple 5V rails).

Yes the MC10EL16 has the advantage that it is still in production and is available in SMT packages. We could even think about using the MC100EP16VA: this is basically the same, but with a higher gain. This would allow for an even larger dynamic range at the input!

As for the termination of the ECL gates, I read the corresponding application notes from ON Semi. I first went for the Y Termination in my design, the same as you do. However I am unsure; maybe the Thevenin termination is better because the voltage ad the Q and Qbar pins is better defined. Also it is only one additional resistor compared to the Y termination, so the disadvantage is not a big deal I think.

I am still a bit concerned about the DC coupling between the ECL gate and the mixer, though.

I started routing the input part, I think I'm going to switch to Thevenin. The layout seems cleaner and simpler. With "Y", I didn't find a good way to route the VTT rail without the differential signal crossing over it. The Thevenin doesn't create a separate rail, it's just a voltage divider between VCC and VEE.

I like the idea of using a differential IF signal. It seems a good idea to decouple the mixer output from the ground noise until it is sufficiently amplified.

No opinion yet about the DC coupling of the ECL gate and the mixer. There is nothing than the output drive strength of ECL gate to limit the current...

If you disconnect the input signal though, should not the 50 Ohm resistor across the inputs bring the differential input voltage to 0?

[ch_scr]

[...]

I started routing the input part, I think I'm going to switch to Thevenin. The layout seems cleaner and simpler. With "Y", I didn't find a good way to route the VTT rail without the differential signal crossing over it. The Thevenin doesn't create a separate rail, it's just a voltage divider between VCC and VEE.

I like the idea of using a differential IF signal. It seems a good idea to decouple the mixer output from the ground noise until it is sufficiently amplified.

No opinion yet about the DC coupling of the ECL gate and the mixer. There is nothing than the output drive strength of ECL gate to limit the current...

If you disconnect the input signal though, should not the 50 Ohm resistor across the inputs bring the differential input voltage to 0?

Yes, the input of the buffer / comperator will go to zero. But the outputs are always inverted from each other, always one high the other low.
For the DBM always the RF power and IF maximum current is specified, but not RF coil DC max current.
With 1u / 100n smd 0805 X7R in parallel very wide band ac coupling can be achieved - a jumper can always be placed later if it turns out to be a problem.

[Mrt12]

I've been experimenting a bit, simulating the design in LTSpice. I've added the current schematic as an attachment.
I like the idea of using the MC10EL16 as input buffer, though it seems a bit tricky to terminate ECL gates properly (schematic also attached).

All the FDAs I found have a Vocm voltage output, which you can use to set the center threshold for a comparator or DAC.
The output of the mixer is floating, isn't it? It's not ground referenced. Does it make sense to loosely bias it to Vocm (R14/R15 in my schematic) to prevent the differential pair from drifting outside of the valid input range? Or are the amplifier inputs always biased against the Vocm anyway?

I as far as components go, I just used what seemed appropriate in the LTspice library. As far as I can see, this design could be run from a single 5V supply rail (or multiple 5V rails).

Yes the MC10EL16 has the advantage that it is still in production and is available in SMT packages. We could even think about using the MC100EP16VA: this is basically the same, but with a higher gain. This would allow for an even larger dynamic range at the input!

As for the termination of the ECL gates, I read the corresponding application notes from ON Semi. I first went for the Y Termination in my design, the same as you do. However I am unsure; maybe the Thevenin termination is better because the voltage ad the Q and Qbar pins is better defined. Also it is only one additional resistor compared to the Y termination, so the disadvantage is not a big deal I think.

I am still a bit concerned about the DC coupling between the ECL gate and the mixer, though.

I started routing the input part, I think I'm going to switch to Thevenin. The layout seems cleaner and simpler. With "Y", I didn't find a good way to route the VTT rail without the differential signal crossing over it. The Thevenin doesn't create a separate rail, it's just a voltage divider between VCC and VEE.

I like the idea of using a differential IF signal. It seems a good idea to decouple the mixer output from the ground noise until it is sufficiently amplified.

No opinion yet about the DC coupling of the ECL gate and the mixer. There is nothing than the output drive strength of ECL gate to limit the current...

If you disconnect the input signal though, should not the 50 Ohm resistor across the inputs bring the differential input voltage to 0?

as ch_scr said, the Q and Qbar outputs are always inverted with respect to each other, so there will be definitely a DC current through the mixer if the input signal is disconnected.

I think a series capacitor is a wise idea. I am thinking about using even two capacitors, one for Q and the other for Qbar, to keep the connection as symmetrical as possible. Maybe this is unnecessary?

I ordered a couple of ECL gates on eBay (MC100EL16). I found a bag with 30 pieces for a good price. As soon as they arrive I can make some tests, hopefully ;-)

[Mrt12]

This is my current design of the zero cross detector and the ECL input stage.
What do you guys think, do the ECL gates provide enough isolation between the mixer and the input connector?

As I said I plan to make a 3 channel device which will be suitable for three cornered hat methodology. So the offset oscillator is common to all three channels.
If only an ordinary DMTD is required, just don't use the third channel.

[tkamiya]

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

[edpalmer42]

I have two nice Datum / FTS 1130 10MHz osc that I want to test. They were pulled from some Telecom freq references. I have not found any data on these but they are in the same package as the high end Datum 1000 osc.

I did some more digging.  No data sheet unfortunately, but better than nothing.

https://web.archive.org/web/19990502022103/http://www.datum.com/prod_fts_1130.html

[chuckb]

I have two nice Datum / FTS 1130 10MHz osc that I want to test. They were pulled from some Telecom freq references. I have not found any data on these but they are in the same package as the high end Datum 1000 osc.

I did some more digging.  No data sheet unfortunately, but better than nothing.

https://web.archive.org/web/19990502022103/http://www.datum.com/prod_fts_1130.html

Thanks for investigating this. I better get the 1130s warmed up for testing!