SMU IV Connections

Hi, there is one 4200 system with 5 SMUs in my lab.<br> Recently, we are going to use the system to measure IV curves for our designed PCB board as shown in the following figure.<br> Basically, there are four terminals on the PCB:<br> terminal 1 is Vin,<br> terminal 2 is GND<br> and the other two&#160;terminals (terminal 3 and 4) are used for current measurements.<br> The voltages of terminal 3 and 4 are dependent on the current.<br> We want to sweep the Vin at terminal 1, and meanwhile measure the current between terminal 3 and 4.<br> How to set SMUs for this measurement since all the Lo&#160;terminals of SMUs are connected together in 4200 system?<br> Should I need one additional 2400 or 2600 to perform this measurement?

So, your terminal 4 is not at GND potential?<br> How big might the voltage at terminal 4 become?<br> <br> I do think you will need a floating amp meter where the LO is not shared with other SMU in 4200.<br> An external 2400 or 2600….. or even Amps terminals of a DMM depending on the values of current.<br> <br> Can you use known small resistor between terminal 3 and 4. &#160;Use a SMU at each terminal too.<br> Both SMU force 0 Amps and measure V. &#160;Your current is (V3-V4)/R<br> <br> A third SMU sweeps V at terminal 1.<br> Terminal 2: &#160;GNDU or use a SMU to force 0V and measure the current flowing into the SMU. &#160;Be sure to set the current limit high enough for all the current that will arrive.

YES, terminal 4 is not GND and actually it is connected to the collector of one BJT.<br> Using a resistor between terminal 3 and 4 is a good idea.<br> However, I am afraid it may break the symmetry of the entire circuits.<br> So, I guess I have to use external DMM 7510 or 2600 to measure the current.<br> Thank you for your help!