Sink current with PXI-4130

[enderWiggin10]

Hi RTRF,

Thank you for further explaining the situation.  I now feel that I understand your 3V supply and you application and testing, but I am still a little foggy as to how the 4130 fits in.

Based on option 1, you did not mention using the 4130 at all, so I assume that you are not intending to use it here.  Is this correct?  If you do not use it, what will you use to measure the voltage of the signal?

For option 2, it appears that you are looking to use the 4130 to sink the current from your power supply while also measuring the current of the output.  Is this correct?  The 4130 is used to source a voltage and the measure the effect of this on the DUT.  Do you actually need to source a voltage and current from the measurement device to your 3V power supply and then measure the result?  Or do you only need to measure the current that your 3V generator outputs?  If you only need to measure the signal, a DMM is capable of sinking the current while measuring.  Would this accomplish what you intend to do?

Please let me know if I am mising anything.

Best,

[RT_RF]

Hi cyclone,

thank you for your reply.You are right:

- for option1, 4130 might not fit. I am not exploring this option, but there should be a way to have a large number of resistors available between my 3V generator and GND, and to have them successively connected to sink an increasing current on my 3V...

- option2 based on the use of 4130 might be easer. And you are correct: i need to measure the current that my 3V generator outputs (fanout). As you know, my purpose is to be able to control precisely the current sunk by my 3V generator outputs: i would increase the sunk current step by step from 50ua to 30ma until the 3V output (measured of course) would drop.

Apparently, the 4130 is capable of doing this with a high accuracy (current  accuracy<0.1%). Is it correct, how would you proceed? 

i don't know about the DMM: is it capable of sinking with a good accuracy the current of my 3V generator? would you have a reference in mind?

regards.

[enderWiggin10]

Hi RTRF,

I apologize for my previous post.  After looking further into the issue, using the method I outlined with a DMM, would actually require 2 DMMs to monitor the voltage and current at the same time, would would also throw the votolage drop of the shunt resistor for current into the equation.  It would be possible to do it with 1 DMM, but this would require a very precise variable resistor in order to extrapolate the current.  This is in fact why the 4130 exists.

The way to proceed is to use the 4130 in current mode and set the voltage limit above your expected value of 3V, let's just set it at 5V.  We can then proceed by setting the current sweep set points starting off at the minimum and then gradually up until the voltage begins to drop.  I recommend not using the 'disabled' state of the SMU because this sets the votlage to 0, and the current to a limit of 20mA.  This might not be desired for you because your source will only go to 200uA as you mentioned before.  You can set the mode to 'enabled' and then set the votlage to 0 and the current to the lowest settting, which should be 4uA, or any other setting as you deem fit for your application.

The main point is that this should work for your application as you have specified for option 2, and I apologize for the confusion before.  Best of luck.

Best,

[RT_RF]

right, it is getting encouraging.

Just a few comments:

you say: "You can set the mode to 'enabled' and then set the (SMU?) votlage to 0 and the current to the lowest settting, which should be 4uA, or any other setting as you deem fit for your application." 0v is the voltage set to the SMU: can you detail?

I guess, by appling 0V as the SMU voltage, my 3V generator will deliver current into the SMU (current sunk by the SMU), this current being limited by the "current limit" i will set and change step after step until it gets so high that it drops my 3V: correct? 

now, i don't get it when you say "The way to proceed is to use the 4130 in current mode and set the voltage limit above your expected value of 3V, let's just set it at 5V". I thought i had to set 0V...could you clarify?

RTRF

[enderWiggin10]

0V would be to set the device to a custom 'disabled' state.  You would want to allow for 5V as your votlage limit to allow the voltage to be sunk in current mode.  This will ensure you do not reach compliance on your votlage level when the power supply is providing the 3V signal to be sunk.

Best,