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Measure count exceeding buffer capacity in TSB

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manikant21
Posts: 4
Joined: January 13th, 2016, 3:19 am
Country: India

Measure count exceeding buffer capacity in TSB

Post by manikant21 » January 15th, 2016, 7:03 am

using TSB for switching measurements with 2636B. Using both the SMU to switch over voltages & measure current continuously. Only constraint is the switching is being done as 110us which is the best to get out of 2636B.

Now the problem is maximum points I can get is 1000 which is too less for me, also no of pointsxtime=total duration of the measurement.

As per requirement, the time has to be fixed at 110us, so the only option left for longer duration & more accurate data is large no of points. Now when I edit the no of points in the code it gives me measurement counts exceeding buffer capacity, how to fix the same? is there a limit to have maximum no of points??

I'm using TSP link.

screen shot of error is attached
Error[img]
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Error in code [img]
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Code
code.txt
code
(58.41 KiB) Downloaded 1537 times
Attachments
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2.JPG (94.1 KiB) Viewed 22941 times

Andrea C
Keithley Applications
Keithley Applications
Posts: 1323
Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: Measure count exceeding buffer capacity in TSB

Post by Andrea C » January 15th, 2016, 11:27 am

In looking through the information, I see you are actually using the TSP-Express internal web page application.

TSP-Express is using the default reading buffers: nvbuffer1 and nvbuffer2.
These buffers can store appx 60,000 readings with timestamps and source values also enabled.
If disable timestamps and sourcevalues, then the number of readings increases to about 140,000.

Since you are using the TSP-Express application, you will be constrained by design choices and assumptions made by that development team. As you found, the GUI of TSP-Express is trying to limit you to 1000 points. You are directly accessing the dynamically generated code and changing the number of points to a higher value. This could have some unintended consequences but will also be limited by the physical size of the nvbuffer.

Can you go back to the beginning and describe what you want to accomplish? What is your DUT? What do you want each SMU channel to do?

manikant21
Posts: 4
Joined: January 13th, 2016, 3:19 am
Country: India

Re: Measure count exceeding buffer capacity in TSB

Post by manikant21 » January 16th, 2016, 11:08 am

Dear Andrea,

Thanks a lot for your reply.
My DUT is RF-Fet & measurement is dynamic ron.Setup is quite simple & mentioned below.

V source (OFF state) for given time ( time can range from 100ms to 1000s) at SMU A (Gate) & SMUB (Drain)
V source (ON state) for given time ( time can range from 100ms to 1000s) at SMU A (Gate) & SMUB (Drain)

Switching between OFF & ON state should be fastest (around 110us).
ON & OFF state time can be same or different, there is no compulsion on these times .

Current (I) will be continuously measured during On,OFF state & during switch over. The more no of points I get, the better it is.

Present program works well except that 1000 points limitation.

Andrea C
Keithley Applications
Keithley Applications
Posts: 1323
Joined: October 15th, 2010, 10:35 am
Country: United States
Contact:

Re: Measure count exceeding buffer capacity in TSB

Post by Andrea C » January 18th, 2016, 2:22 pm

Sounds like you may need to take a more customized approach to the measurement. TSP-Express web page GUI might not be the best choice.

The fastest measure rate with the 2636B will be 20KSamples/sec or every 50usec. To achieve this measure rate, you must use fixed measure range and measure asynchronously from any change in source value.
Will this be fast enough to give meaningful info for dynamic Rdson?

With asynchronous trigger model, timing of measurements can be separate from timing for sourcing.
Below is graphed the timestamp vs. measured voltage using this approach. It starts measuring, then a voltage pulse is sourced.
We can see the before, during and after the voltage pulse.
The delta time is 50usec.
2600B_ASYNC_Sampling.PNG
2600B_ASYNC_Sampling.PNG (9.25 KiB) Viewed 22910 times
The model 2651A can do this same task but can deliver 1usec sample intervals.

Is your RF FET a GaN device? Would you need the gate SMU to activate before the drain SMU?
Maybe some timing diagrams of the Gate and Drain signals vs. time with indication of when measurements should occur will help to clarify the various requirements.

manikant21
Posts: 4
Joined: January 13th, 2016, 3:19 am
Country: India

Re: Measure count exceeding buffer capacity in TSB

Post by manikant21 » January 20th, 2016, 4:08 am

Dear Andrea ,

Thanks a lot for the reply, u made it so clear & better for me especially on fixed range part.Please find attached image for measurement setup.

Yes, it's a GaN device & 50usec should be good to start with for data collection.

I do need gate smu & presently I'm using the second smu of 2636B for the gate, however, I do wish later to add 2657 high voltage SMu for the drain & use 2636b juts for the gate.In that case, I'm planning to use 2657 as the second node.

In terms of the gate or drain getting activated will prefer both to switch at the same time or at least with the minimum possible delay between them & if there is delay than would like to switch drain first & gate later. Bcoz drain typically has a high voltage in off state & if gate gets ON first than the delay in drain switching will subject device to high bias & which will lead to damage.
D-Ron.JPG
D-Ron.JPG (77.35 KiB) Viewed 22901 times
Do let me know if u need any more information, will wait for your kind reply.

manikant21
Posts: 4
Joined: January 13th, 2016, 3:19 am
Country: India

Re: Measure count exceeding buffer capacity in TSB

Post by manikant21 » February 1st, 2016, 1:51 pm

Dear Andrea,

I'm waiting for your reply, let me know if you need any information from my side.

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