2/3 Wire analyzer

[Siciem]

Im using ni-elvis and labview for adquire semiconductors V/I curves, I know using 2 or 3 wire current-voltage analyzer block it's easy to adquire.

I'd like a way to adquire the curve without using that block. I need a way to use the dmm ports with labview and be capable of handle the current (for bjt curve).

On the other hand I'd thank a way to see what is inside the  3 wire current-voltage analyzer block in order to understand it and be capable of coping it.

Thanks

Yours

[charlesy]

Hello Siciem,

Take a look at page A-33 of the Theory of Operation in the NI ELVIS II Manual:

https://www.ni.com/docs/en-US/bundle/374629c/resource/374629c.pdf

It shows the block diagram of the Impedance Analyzer. Measure voltage at the output of the FGEN (internally connected to the DUT+ terminal, and referenced in software as _dutPos). Measure current at the output of a transimpedance amplifier (software channel name: _dutNeg). That is actually a voltage measurement -- you need to divide it by the gain resistor value to get current.

The approximate values for these three resistors are 100k, 9.09k, and 64.9 Ohms.

You can pull the calibrated values of these three resistors out of the EEPROM. To do that, see the source code for the ELVISmx Soft Front Panels. They are installed here:

C:\Users\Public\Documents\National Instruments\NI ELVISmx Source Code\

The code is a bit involved, but focus on the State Cases in the upper loop -- particularly "Read EEPROM" and "Measure".

Note that the ELVIS II DMM is a single-point device (routed only through the three banana jacks on the side), so you can't measure fast enough or with predictable timing to get meaningful phase information for your impedance calculation. Instead, the impedance analyzer uses Analog Input lines for waveform acquisition. 

I hope this is helpful,

Charles Y.

National Instruments