DMTD board

[Mrt12]

Didn't need to do that, as my lab power supply does it for me ;-) Including the termination resistors, the current consumption is 65mA. Theory says that ECL current consumption doesn't change with frequency, and this is EXACTLY what I measured here:

DC: 65mA
1MHz: 65mA
10MHz: 65mA
100MHz: 65mA
1GHz: 65mA

So it is indeed quite power hungry, but considering the fact that this is indeed a very simple limiting amplifier with a decent input dynamic range, I would say this is not bad, is it?

What do you think by the way about the output level? 700mV, should be enough to drive the mixers. I assume the MC1650 are not much better. Are they?

[thinkfat]

Didn't need to do that, as my lab power supply does it for me ;-) Including the termination resistors, the current consumption is 65mA. Theory says that ECL current consumption doesn't change with frequency, and this is EXACTLY what I measured here:

DC: 65mA
1MHz: 65mA
10MHz: 65mA
100MHz: 65mA
1GHz: 65mA

So it is indeed quite power hungry, but considering the fact that this is indeed a very simple limiting amplifier with a decent input dynamic range, I would say this is not bad, is it?

What do you think by the way about the output level? 700mV, should be enough to drive the mixers. I assume the MC1650 are not much better. Are they?

I'm more interested in the transients. Did you measure the consumption with the mixer connected?

I think 700mV is enough for a Schottky diode mixer.

[Mrt12]

Ah yes I see. I can try that tomorrow but I doubt my scooe is fast enough to see them.
I had no mixer connected but an AC coupled 50Ohm load.

[tkamiya]

Everything is in aluminum case and seems to be functioning.  One of the 3 terminal regulator is getting awfully hot, so I'll have to look at that later.  I believe it's -5V.  All others are somewhat warm to touch.

I've heard there is a convention folks follow in terms of what goes into Ch A and Ch B.  Anyone know which one is DUT and which one is reference?

If anyone is using TimeLab and TAPR TICC, I'd appreciate sharing of setup parameters.

[5065AGuru]

Taka,

I use the extra outputs to drive a dual one shot that drives an LED for each channel.

As far as which input to use for DUT and REF...

When I run plots on Quartz I like to set the counts at a low value that is slowly going up.

I want the aging to cause the counts to slow and then start back down.

On a good  oscillator you end up with a nice parabola which you can see in plot1 in the DMTD tutorial post.

This way I can stay in the lower end for a longer time.

I pick the DUT/REF connection that causes this to occur.

Cheers,

Corby

[thinkfat]

Ah yes I see. I can try that tomorrow but I doubt my scooe is fast enough to see them.
I had no mixer connected but an AC coupled 50Ohm load.

The scope will do fine I think. You should at least see "something", qualitatively at least.
I'm most interested if you can really drive the mixer, especially the LO capacitively.

[Mrt12]

I'm most interested if you can really drive the mixer, especially the LO capacitively.

Just tested that. Setup was as follows:

HP 33120A function generator, square wave, 600mVpp, 5 MHz into ADE-1+
HP 8663A signal generator, 5MHz, 0dBm, into the ECL gate
output of the ECL gate, capacitive coupling, into ADE-1+
IF output of ADE-1+ to the scope via lowpass filter as shown in my schematic.

Result on the scope: a nice sine-like signal with about 800mVpp amplitude. I can reverse the mixer's RF and LO ports and the result stays the same.
I can vary the signal generator's amplitude between -12dB, and approx. 5dBm withouth any noticeable change on the scope display.
Of course I cannot change the function generator amplitude as much because this one is directly connected to the mixer.

Does that sound acceptable? I can make a scope picture later.

[Mrt12]

Hello again

so as I promised previously, I performed some additional tests with an ADE-1+ mixer. I use the configuration as shown in the schematic attached.
I used the following test equipment:
HP 8341A signal generator with 0dBm output power, connected to LO port of ADE-1
HP 8663A signal generator with 0dBm output power, connected to the ECL gate
the ECL gate is capacitively coupled to the ADE-1
the IF output is measured with the scope.
The signal generators are synchronized together with an external 10MHz reference, such that I can adjust them to exact offset frequencies.

I measured the IF output signal up to 500MHz, the max. specification of the ADE-1. As we can see, at 500MHz, it does have a significant DC offset; however, below 500MHz, the IF signal looks quite acceptable. However I was wrong previously, it is not 800mVpp but merely around maybe 600mVpp. But I guess this should still be acceptable.

We also need to take into account that I currently drive only ONE of the mixer ports with the ECL gate. But I assume the mixer's properties will not change much if both ports are driven like so, as the ECL gates anyway are 50 Ohm sources.



Edit: I needed to attach the 500MHz measurement as JPG. The forum software rejected the PNG picture, for whatever reason :-O

[tkamiya]

A couple of things I'm concerned about....

It is typically known that diode ring DBM needs high IF input, typically in tune of 7dB.  I wonder what effect it will have when it falls below this level?

On my own setup, I didn't use long neck SMA but used a regular one, and connected to front panel mount N/SMA via short piece of coax.  Initially, I was going to use semi-rigid line but I don't have the size I need.  Then I was wondering if this is really necessary.  From there, there will be a pair of longish flexible cable to DUT and REF anyway.  What do you folks think?

Here's front panel of completed setup.  Little silver box is just a boxed up OCXO.  I can adjust +/-4Hz off 10MHz nominal.  I see many examples where DDS was used for Lo.  I'm still not clear what kind of stability is required.  But Bill Riley did it that way on his implementation.  Otherwise, I'll just setup a few HP11801 already set to proper offset.  I'm using TAPR TICC because I already have it handy.

I put LED on front panel driven by extra gate on output side.  If I have to do this over again, I'd probably steal another gate from parallel driver and have Aux output.  During testing, having scope connected to it was "instrumental."

[5065AGuru]

Taka,

Saw your mention of the LED!

Realized since the simple dual mixer monitor outputs are square wave you can probably just drive two LEDs through a resistor directly!
My original NBS106B dual mixer has very narrow pulse outputs so that's why I mentioned the  74XX221 circuit to drive the LEDs.
I'm pretty sure my other ones have square waves out so no need for the one shots, just a buffer.
Silly me!

Your unit looks nice.

Cheers,

Corby

[tkamiya]

Corby,

I don't think I would do that - that is, tap off of main output via register and drive an LED.  I am not sure what kind of load LED would present...  (I'm using 680 ohm series register)  I'm even hesitant to Tee out the output into scope and counter.  Reflection and stray capacitance might have some impact.  I was going to try this today and I got side tracked.  I'd prefer keeping output as straight 50 ohm as I can.

You mentioned NBS106B few times.  I know the design but you have a real unit produced by NIST/NBS? 

[Mrt12]

Hey Taka,

"It is typically known that diode ring DBM needs high IF input, typically in tune of 7dB.  I wonder what effect it will have when it falls below this level?"

well, Minicircuits has an excellent application note on this. They say that it is no problem to operate a mixer with a couple dB lower LO power. As you can see from my tests, the ADE-1+ works well with 0dBm to 1dBm input power. But I agree to your point and maybe an ADE-1L+ would be even better. This is even specified in the datasheet for 0dBm LO. But even for the ADE-1+ I don't see much problems, as we saw from my tests.

[thinkfat]

Driving a mixer too low is mostly impacting the IP3 and linearity, no? That's not a problem for this application. Besides, the ECL gates driving the mixer are really a good idea. That provides a lot of independence.

[Mrt12]

Driving a mixer too low is mostly impacting the IP3 and linearity, no? That's not a problem for this application. Besides, the ECL gates driving the mixer are really a good idea. That provides a lot of independence.

Yes, I totally agree. The ECL gate input buffer is indeed one smart idea from Corby! It allows for a wider input dynamic range and also suppresses amplitude fluctuations (more or less).
The only unknown is whether the ECL gates are noisy (i.e. increase the phase noise) in a manner that influences the measurements. But from the instrument noise floor Corby posted on page 1, it seems quite good.

[notfaded1]

I think this design is very similar to how Efratom did it in their commercial DMTD product so yeah... it's legit. 

[5065AGuru]

Taka,

The monitor outputs are separate from the main outputs!

So you can load them to your hearts content with an LED/resistor or otherwise!

Cheers,

Corby

[Mrt12]

Dear colleagues
during the past days I finished my dual DMTD and the corresponding PCB.
I just optimised the BOM and ordered the PCBs, hopefully they will arrive next week.
The schematic is attached. I am very curious how well it will work and what noise floor I will get!
To get started and save some costs on the OpAmps, I decided to populate only the first OpAmp stage with the LT1007 and skip the 2nd OpAmp stage with the OP37.
Besides that, I will use the HP 5372A Timing Analyzer I have, this would allow to measure 2 oscillators against each other.
Later on, I plan to make a simple time-tag counter with 4 channels. This would then allow to measure 2, 3 or even 4 oscillators against each other!

I also prepared some maths for a "four cornered hat". If four oscillators are heterodyned with one common offset oscillator, I think a similar approach as for the three-cornered hat would be possible and therefore would allow to determine the absolute oscillator stability.
This is because we get 6 different measurements when we time-tag the four outputs:

1 vs 2
1 vs 3
1 vs 4
2 vs 3
2 vs 4
3 vs 4

so we have 6 possible measurements and 4 unknowns (the stabilities of the four oscillators), so we can do the math and solve this overdetermined equation system. The same as for the three-cornered hat! it will be very interesting whether this would work.

Also the inter-channel isolation will be an interesting topic as I tried to make a compact layout. However I decided to use a 4layer PCB with proper power and ground planes, so the EMC should be acceptable - as we already saw that the reverse isolation of the ECL gates is around 60 to 80 dB, even with my crappy manhattan-style test circuit I showed a couple weeks ago.

If there is interest I will keep posting updates on this as well!

[5065AGuru]

Hi,

Here is a comparison test between two BVA oscillators that Tom Van Baak made simultaneously using the Simple Dual Mixer against a TimePod.

The first 2 plots shows ADEV and MDEV as measured by both systems and the second plot shows the frequency "wander" between the BVA oscillators using 10 Second averaging.

Very nice data showing how good the Simple Dual Mixer can perform!

Cheers,

Corby

[Mrt12]

Dear colleagues
today I received my PCBs from Eurocircuits. I immediately decided to populate the input stages with the ECL gates and the mixers, so I could do first simple tests!
Further, I also changed the mixer and decided to use the ADE-2+ instead of the ADE-1+. This will allow only a lower frequency of 5 MHz, but at least 1 GHz for the upper frequency.
Then I tested the beat note output from the mixers after the lowpass filter for various input frequencies. Again I set my signal generators with 10 Hz offset to each other and tested different input frequencies. The output beat note stays quite nice and constant up to 2 GHz input frequency. I didn't test further, as this is definitely more than enough for me! Beat note amplitude around 500mVpp.

Further I tested the isolation between the DUT inputs and also between the DUT input and the offset oscillator input.

The further is very good, around 110 dB (measured with my HP 3577A network analyzer, unfortunately only up to 200 MHz). The isolation between the DUT inputs and the offset oscillator input is a bit worse, around 95 dB. But I guess this is stil acceptable, is it.

The beat note output does not vary with input amplitude as long as it is in the range of -25 dBm to +12dBm. I did not test higher amplitudes. If the input amplitude is lower than -25 dBm, the output becomes more and more sinusoidal (it is normally some sort of triangle wave).

The return loss for the DUT inputs is around -30 dB, whereas the input return loss for the offset oscillator is a bit worse, around -20 dB. I guess this is because I neglected "proper" RF design criteria for the offset oscillator's traces and just used a simple Y connection for them. Still, I consider -20dB good enough for the offset osc.

Unfortunately I don't have suitable scope probes to measure the output signals from the ECL gates - but as the mixer output seems to be quite stable, I assume the ECL gates work as they should.

As I don't have the OpAmps ready for the gain stage, I cannot test further yet, but I think the results so far look promising, do they! Let's see what the noise floor will be. I am very curious.

By the way, the ECL gates are indeed power hungry, this little part with only 4 gates already consumes 270mA! :-D

[tkamiya]

Very nice!

I'm thinking of going WILD and do 8 channel.  A have a questions for you.....
What are you using for off-set oscillators?  Seems you have something frequency agile?
Over the course of thread, some discussed transformers at input.  It appears you opted to go without.  What was your thought process?

[Mrt12]

Hi Taka,
indeed 8 channel would be good as well. We can proof that if there are three or more channels, it is possible using some linear algebra that the absolute allan variances of the individual oscillators can be calculated, so it can indeed make sense to use 8 channels if you have so many oscillators :-)

Concerning the transformers. Indeed I didn't use them. I cannot see any advantage of those. Neither my scope, spectrum analyzer, network analyzer, counter, signal generator or impedance analyzer does have transformers at its input but uses N or BNC connectors connected to ground. So I don't see why exactly here in THIS very application we should have a problem with ground loops?! but, if necessary, it will be easily possible to connect a transformer externally.

However they also have a lot of disadvantages, for example many transformers are not as wideband as my input stage is currently without transformers.

[Mrt12]

Hi all
today I wanted to continue testing of my DMTD, but I am still waiting for the OpAmps I ordered.
However, I found that I do have a bunch of OPA27 in my parts box, and at first glance, it seems that they are an acceptable alternative to the LT1007 I planned originally to use. So instead I populated the OP27. I don't have the LM311 comparators yet, but I will still be able to measure the output signals from the OpAmps!

That's what I did now. I used a HP 8663A signal generator for the offset oscillator, and a HP 8341A signal generator for the DUT input. The other DUT input was terminated with 50 ohms.

I then measured the mixer output signal, as well as the output signal of the first OpAmp gain stage and the 2nd gain stage for different offset frequencies.I set the offset signal generator 10 Hz or 1 Hz low compared to the DUT oscillator.

For the measurements, forget about the Y scale - I used an 1:10 probe but didn't tell the scope, so voltages are 10 times lower.

We can see from the graphs that the slope at the 2nd OpAmp stage is around 2.5 V/ms for 1 Hz beat note, and around 10 V/ms for 10 Hz beat note. When we compare this to Bill Riley's famous "Small DMTD system", it seems that these values are in a similar order of magnitude, and, further, the waveforms look  also quite similar. The slope of my OpAmps is perhaps even a bit steeper.

As soon as I receive the LM311 comparators, I have everything ready so I can generate a proper 5V TTL output which I then can connect to my HP 5335A counter or 5372A timing analyzer.

Again I also tested the output signals of the OpAmps when the input frequency and power is varied. The current design seems to work fine up to 2.5 GHz, I didn't test further. I think so far it looks good ;-) a noise floor test cannot be done yet as I don't have a proper output signal I can connect to my counter.

[tkamiya]

I am working on THE Corby design.  It seems base line graphs are one order of magnitude worse than expected, so I've started poking around.    Input is fed by a common source.  Difference input is 1Hz offset.  Looking at numbers coming out of TIC on a terminal session, I can clearly see fairly repetitive and predictable wobble between channels.  Scoping the output, yup, I see relative shifts of the output, occasionally as much as 100 micro seconds.  Counters are confirmed "not in the equation."   

Looking at power bus, it's incredibly dirty.  Not a regular ripple, but more of white noise at 50mV or so.  I am finding this very odd, since I am using a linear supply I've made just for this setup.  My plan is to try running it with battery and see what happens.  Source of this white noise is unknown at this point.     

Just reporting in....

[tkamiya]

I kind of have my setup stabilized now.  Can someone who is clear headed help me with this?

DUT and reference is 10MHz
Difference oscillator is 1Hz offset
Using TIC, I see 0.nnn,nnx where x is changing about 4 counts.

What does it indicate on 1s Adev? 

[Mrt12]

Taka,
have you found out why your Power Bus was so dirty? was it the power supply? or switching transients from the logic gates?
As for your other question I'd say: you see a change of around 4 microseconds, i.e. 4e-6. Your DMTD mixes 10 MHz down to 1 Hz, this is factor 1e-7, so I'd say your stability is around 4e-13?
Not 100% sure as you would normally take a timeseries of readings and then calculate the AVAR from that.