Pocket-Sized 6 GHz 1 TS/s ET Scope

[joeqsmith]

To get some idea how the gain changes with temperature, again, looking at channel 2.   Here is the start of the previous dataset, again the first test right after reworking the board with it cold.   I repeated this test about 3 hours later with the scope running other tests that entire time.  Notice, the gain did not change at all.   

It's possible that things were not stable prior to reworking the board.  That couple of hours I mentioned working on it wasn't an embellishment.   I would guess I touched 20 joints conservatively but most likely more in the order of 50. 

[joeqsmith]

Showing channels 1-4 at the start of run 6.  Again, this is after reworking the board and with it having been running for 3 hours.    We can clearly see there is a gain error but notice the spread of the positive apex is tighter than at the negative apex.  The scope has always behaved this way but that spread has opened up with the increase in gain.   I can't tell from looking at the manual if these are considered normal.   

[SJL-Instruments]

Looking at post 197 showing all 4 channels prior to rework.  You can see, they were never really matched well.  After rework, they have spread apart even further.   I would need to run some tests to determine how much is due to gain vs offset but it sounds like it currently isn't  possible to correct for them anyway.  Are there plans to add some sort of alignment procedure to your software that could be saved?

The next revision of the software has a one-click tool for trimming the DC offset.
This will of course not fix any gain error. You can try testing the DC linearity with the internal trigger to see if there's an overall scaling error. Global scaling error should be around 1%, with a linearity of around 0.1%.
The frequency-dependence of the gain error cannot in general be fixed for a sampling scope.

When you specify the maximum DC RMS (section 1.5), are you running internal trigger with all inputs shorted?   

The specification applies to measuring any stable signal and analyzing the resulting RMS deviations from the mean.
Running internal trigger with inputs shorted is a special case of this.

Again, looking at channel 2.  Showing the first set of data after I reworked the board.  We are looking at sweeps on the X-axis, hourish of time.  This is subtracting the mean from the signal as previously described.  Note how the noise level decreases as it warms up.

This is known behavior - after warmup, the RMS noise should be somewhat better than the specification.

Showing channels 1-4 at the start of run 6.  Again, this is after reworking the board and with it having been running for 3 hours.    We can clearly see there is a gain error but notice the spread of the positive apex is tighter than at the negative apex.  The scope has always behaved this way but that spread has opened up with the increase in gain.   I can't tell from looking at the manual if these are considered normal.   

The spread occurs primarily in the 11-11.5 ns region and should be unrelated to signal level. It should be lower after 12 ns.
This is known behavior and limits the minimum ENOB specification at 1 GHz.

[joeqsmith]

This is known behavior - after warmup, the RMS noise should be somewhat better than the specification.

The spread occurs primarily in the 11-11.5 ns region and should be unrelated to signal level. It should be lower after 12 ns.
This is known behavior and limits the minimum ENOB specification at 1 GHz.

Thank you very much for supplying those valuable tips!! 

You can try testing the DC linearity with the internal trigger to see if there's an overall scaling error. Global scaling error should be around 1%, with a linearity of around 0.1%. 

Before working with the internal trigger, I would want to implement your other correction as I assume the internal trigger is considered low.

We also have a check that the extracted fit voltage lies between the 25th and 75th percentile of the CDF. If not, we revert to using the interpolation method. This only matters at low triggers/sample or samples/cdf, when the data is very noisy and the fit might blow up.

If you keep Nmax above 500 and K above 20, this shouldn't be an issue.

Showing the same 4 sets of data for channel 3.   White was the initial testing from post 197,  Red was repeating this test prior to reworking the board, Green was taken when the scope was cold right after rework and Blue was after 3 hour warmup after rework. 

I am using the absolute values to provide you with a better view of the gain and offset as well as the different in noise levels between the positive and negative apex.   Note that noise is still higher in the positive region.  Maybe a bit of noise on one of the supplies.  Maybe it's normal.  It has always been there and guessing what aggravates the glitches. 

Verdict it still out on if these glitches will show up after rework.  The plan is to run the hardware up until the software is ready, or until I get bored watching it... Which ever comes first. 

[joeqsmith]

We also have a check that the extracted fit voltage lies between the 25th and 75th percentile of the CDF. If not, we revert to using the interpolation method.

Just to make sure, using your example from 4.3.3, the CDF for the fit voltage would be 0.500 which is within your 0.27&0.75 criteria, meaning use the Gaussian fit rather than interpolation?   

[SJL-Instruments]

Thank you very much for supplying those valuable tips!! 

We've added these notes to the next manual revision as well.

Before working with the internal trigger, I would want to implement your other correction as I assume the internal trigger is considered low.

Could you clarify what you mean by "the internal trigger is considered low"?
We'll send you a pre-release version of the software today or tomorrow that implements the DC offset trim.

Showing the same 4 sets of data for channel 3.   White was the initial testing from post 197,  Red was repeating this test prior to reworking the board, Green was taken when the scope was cold right after rework and Blue was after 3 hour warmup after rework. 

I am using the absolute values to provide you with a better view of the gain and offset as well as the different in noise levels between the positive and negative apex.   Note that noise is still higher in the positive region.  Maybe a bit of noise on one of the supplies.  Maybe it's normal.  It has always been there and guessing what aggravates the glitches. 

Thanks again for supplying this data. The noise from this plot is considered within specification - RMS deviation from mean waveform should be ~1 mV or lower. The zero-crossings are within the ±50 ps (±20 ps typ) global timebase shift specification.

Just to make sure, using your example from 4.3.3, the CDF for the fit voltage would be 0.500 which is within your 0.27&0.75 criteria, meaning use the Gaussian fit rather than interpolation?   

First compute the 0.25 and 0.75 percentile from the CDF using the interpolation method (i.e. the first and third quartiles in voltage). In this case, this would be at 0.474V and 0.477V. The check is to verify that the voltage obtained from the Gaussian error function lies within these two bounds.

[joeqsmith]

Before working with the internal trigger, I would want to implement your other correction as I assume the internal trigger is considered low.

Could you clarify what you mean by "the internal trigger is considered low"?

Your initial comment was:

This only matters at low triggers/sample or samples/cdf, when the data is very noisy and the fit might blow up.

You didn't define "low", but the manual states:

When no trigger is present, the scope will trigger off its internal clock (100 Mtrig/s) until a valid trigger source returns.

and also:

The main limitation of the CDF sampling technique is for signals with infrequent trigger opportunities (500 ktrig/second or lower).

By low, did you mean < 500ktrig/sec?  If so, internal trigger does not fall into that category? 
 

Thanks again for supplying this data. The noise from this plot is considered within specification - RMS deviation from mean waveform should be ~1 mV or lower. The zero-crossings are within the ±50 ps (±20 ps typ) global timebase shift specification.

Thanks.

Just to make sure, using your example from 4.3.3, the CDF for the fit voltage would be 0.500 which is within your 0.27&0.75 criteria, meaning use the Gaussian fit rather than interpolation?   

First compute the 0.25 and 0.75 percentile from the CDF using the interpolation method (i.e. the first and third quartiles in voltage). In this case, this would be at 0.474V and 0.477V. The check is to verify that the voltage obtained from the Gaussian error function lies within these two bounds.

   This is why I ask.  Something so simple, left to my own, I will get it wrong.    I have gone ahead and made this change and will try it out tonight. 

[SJL-Instruments]

Your initial comment was:

This only matters at low triggers/sample or samples/cdf, when the data is very noisy and the fit might blow up.

You didn't define "low", but the manual states:

When no trigger is present, the scope will trigger off its internal clock (100 Mtrig/s) until a valid trigger source returns.

and also:

The main limitation of the CDF sampling technique is for signals with infrequent trigger opportunities (500 ktrig/second or lower).

By low, did you mean < 500ktrig/sec?  If so, internal trigger does not fall into that category? 

Here we meant that the fit may give noisy results when the setting for "triggers per sample" (i.e. Nmin and Nmax in the Advanced CDF Settings) is low. This is unrelated to the trigger rate. Apologies for any confusion.

[joeqsmith]

Apologies for any confusion.

No problem.  Always best to ask.   

Before writing code to sweep the DC, I decided to try shorting the inputs.  Interesting, without that last change it will create NaNs.  I assume expected.  With the check added,  it has been running for about 15 minutes now without a fault.   So it does appear to be required in some cases.   You may want to include that in the manual as well.

[SJL-Instruments]

Before writing code to sweep the DC, I decided to try shorting the inputs.  Interesting, without that last change it will create NaNs.  I assume expected.  With the check added,  it has been running for about 15 minutes now without a fault.   So it does appear to be required in some cases.

Is this in your custom software, or our software? The check should not be required for shorted inputs - it's there only for low-sample situations where the data is very noisy. May be worth tracing down where the NaNs are coming from.

[joeqsmith]

Is this in your custom software, or our software? The check should not be required for shorted inputs - it's there only for low-sample situations where the data is very noisy. May be worth tracing down where the NaNs are coming from.

My software.  It's very possible I am still not understanding your fitter math.  Attached data is with short applied to channel 1.  No CDF data falls within the 0.9 to 0.1 range.  For now it just sets the NaN as you don't define what to do in this condition and I didn't ask.       

Sweeping DC (single ended only), appears. linear.

[SJL-Instruments]

My software.  It's very possible I am still not understanding your fitter math.  Attached data is with short applied to channel 1.  No CDF data falls within the 0.9 to 0.1 range.  For now it just sets the NaN as you don't define what to do in this condition and I didn't ask.       

Sweeping DC (single ended only), appears. linear.

Thanks for the clarification. In this situation, the official software reverts to the 0.5 CDF interpolation method.
***
In fact, we revert to the interpolation method unless there are at least 2 points in the 0.5-0.9 range and 2 points in the 0.1-0.5 range. This is to prevent single outliers from blowing up the fit.

[joeqsmith]

Thanks for that info.  I'll add that check to my software as well.  Goal of this software is really just to give me an easy way to test your hardware/firmware while I wait for your software to catch up.   

Tonight's test, collecting some long high res data sets.  Well... compared to my typical 1-4ns tests, its long...   

[joeqsmith]

In fact, we revert to the interpolation method unless there are at least 2 points in the 0.5-0.9 range and 2 points in the 0.1-0.5 range.

I want to make sure I understand this simple statement.  So 2 data points of 0.5 gives us 2 points in the 0.5-0.9 range and 2 points in the 0.1-0.5 range. Details details...

[SJL-Instruments]

In fact, we revert to the interpolation method unless there are at least 2 points in the 0.5-0.9 range and 2 points in the 0.1-0.5 range.

I want to make sure I understand this simple statement.  So 2 data points of 0.5 gives us 2 points in the 0.5-0.9 range and 2 points in the 0.1-0.5 range. Details details...

Luckily, this cannot happen, since the returned values are expressed as an integer fraction over 255 (odd). 

[joeqsmith]

Luckily, this cannot happen, since the returned values are expressed as an integer fraction over 255 (odd). 

So you want it coded as written where a value of 0.5 is included in both bins?  So 3 points minimum?

[SJL-Instruments]

So you want it coded as written where a value of 0.5 is included in both bins?

In our software, we check for 2 points satisfying 0.5 < x < 0.9 and 2 points satisfying 0.1 < x < 0.5.
Whether you include the endpoints has no effect on the behavior, since none of the values 0.1, 0.5, 0.9 can occur exactly given the serial encoding scheme.

[joeqsmith]

1.1 states the absolute input voltage is +/-1.2V or 2.4V full scale.  1.5 states vertical resolution is 12-bits or 560uV.   With this in mind, showing a 10MHz sine applied, 5ps resolution.  Please explain the steps.   

[SJL-Instruments]

1.1 states the absolute input voltage is +/-1.2V or 2.4V full scale.  1.5 states vertical resolution is 12-bits or 560uV.   With this in mind, showing a 10MHz sine applied, 5ps resolution.  Please explain the steps.   

We cannot reproduce these steps with the official software, looking at a similar timebase/voltage range and with a 10 MHz sine wave. (See attached screenshot.)
Can you see the steps using our software?

[joeqsmith]

Yes, I can show it with your software but the difference is the source.  We are seeing effects from my old Marconi 2024.  Time to ditch it and go with the old HP8640B cavity. 

[joeqsmith]

About 48 hours of running various settings, signals and the hardware appears stable. 

The new software seems to cover the basics.   If I change the waveform,  do I have to delete all the min / max waveforms and recreate them?  There is no simple reset?   Yes, I read the manual.  So, simple example.  Connect your LiteVNA to channel 1.  Set the Lite to 1GHz CW.   With your software, enable the min/max.   Now set the Base to 10ns / div.   Let it sweep.  Now set it to 100ps.    I am able to reproduce this. 

Now change the Base to 200ps then back to 100ps.  All it correct, except, note on the far right.       

[SJL-Instruments]

If I change the waveform,  do I have to delete all the min / max waveforms and recreate them?  There is no simple reset?   Yes, I read the manual.  So, simple example.  Connect your LiteVNA to channel 1.  Set the Lite to 1GHz CW.   With your software, enable the min/max.   Now set the Base to 10ns / div.   Let it sweep.  Now set it to 100ps.    I am able to reproduce this. 

Now change the Base to 200ps then back to 100ps.  All it correct, except, note on the far right.       

Thanks for the feedback. We'll add a "clear" button to the official release, and/or mark the waveform data as invalid after the timebase is changed. For now, you can change the formula (to e.g. "maxhold(CH1)+1"), press enter, and change it back. (Or you can delete and recreate the waveforms, as you stated.)

[joeqsmith]

Overall, the new software seems easy enough to use.    Manual is coming along.     

Maybe consider pressing the Min/Max Hold once they have been enabled, resets or erases the waveforms rather than adding more of them.   How many min max waveforms for channel 1 does one need?    

3.4.4 FFT does not mention the THD feature.   The software shows invalid.  Is it implemented and not documented, or just a place holder?

One person had asked about tracking the rise time.   Can you add histograms, averages, RMS.... to the measurements?    Currently you can only display 8 measurements.  You may need to make use of the upper right area of the display.   

Can histograms be added for math waveforms?

What is the limiting factor in the 200 mVPP trigger limit?  I assume you require a minimum of that value.    Consider that a resistive probe may be 20:1.  Even old TTL would not meet that level.   Maybe I am not understanding the spec.   

[SJL-Instruments]

Maybe consider pressing the Min/Max Hold once they have been enabled, resets or erases the waveforms rather than adding more of them.   How many min max waveforms for channel 1 does one need?    

We'll remove the button if both a minhold and maxhold for the channel are present. The user can modify the math expressions in the added channels, so we'd re-enable the button if one (or both) expressions are altered.

3.4.4 FFT does not mention the THD feature.   The software shows invalid.  Is it implemented and not documented, or just a place holder?

The THD will display as invalid if there isn't enough resolution to get an accurate measurement. You should have five full periods (ideally 10) to get a meaningful result. We'll clarify this in the manual.

One person had asked about tracking the rise time.   Can you add histograms, averages, RMS.... to the measurements?    Currently you can only display 8 measurements.  You may need to make use of the upper right area of the display.

It's easy enough to allow multiple rows of measurements at the bottom. Our first thought is to have a window open when you click a measurement, which allows editing of the measurement, as well as displaying the histogram, trend, average, RMS, percentiles, etc.
We can add an option to pin some or all of this information to the upper right as well.
(By default, the upper right area is unused so that the software can be docked to one half of the screen without issue.)

Can histograms be added for math waveforms?

Yes - we can likely get this in by tomorrow's release.

What is the limiting factor in the 200 mVPP trigger limit?  I assume you require a minimum of that value.    Consider that a resistive probe may be 20:1.  Even old TTL would not meet that level.   Maybe I am not understanding the spec.   

The trigger will work below 200 mVpp, but at a reduced bandwidth. At low amplitudes, you might need to bump the trigger level up or down by a few mV to get a stable trigger. The limit stated in the manual is a conservative guideline.

[joeqsmith]

Indeed, at 5.8GHz the required level is different than 1GHz.  Is the sensitivity vs frequency defined somewhere?   I assume that we can bias that 200mV anywhere as long as we stay within the common mode range (+/-950mV). 
   
0.2 X 20 (probe attenuation) or 4V swing which is CMOS.  Even if you work reliably at 100mvp-p, or a 2V swing, that rules out most logic?  Are you expecting it to work with say LVDS and a 20X resistive probe?    The manual doesn't  offer any suggestions or guidelines when it comes to probing.   

The THD will display as invalid if there isn't enough resolution to get an accurate measurement. You should have five full periods (ideally 10) to get a meaningful result. We'll clarify this in the manual.

Is the THD in your software calculated differently than the calibration certification?  If the settings are critical as far as replicating what you call out, you may want to define them.