Creating Two Bipolar Channels on SMU NI PXIe-414x

Updated May 31, 2023

Reported In

Hardware

  • PXIe-4140
  • PXIe-4141
  • PXIe-4142
  • PXIe-4143
  • PXIe-4144
  • PXIe-4145

Issue Details

I have NI PXIe-4141 SMU. From the white paper: Cascading the Outputs of the NI PXIe-4140/4141/4142/4143/4144/4145, I see, that by cascading SMU's channels it is possible to have up to ±20 V bipolar output. But the article has a mention: "Expansion of the schematic in Figure 1 to create two bipolar ±2VDCmax channels is not recommended.".
Why it is not recommended to create two bipolar outputs using PXIe-4141?

Solution

The fact is that this SMU's channels are sharing same LO and output voltages of the channels will be slightly different even if the same output was set. As an example when the PXIe-4141 is configured as shown in Figure 1, where DUTs sharing same GND. We have to consider that current can flow between channels through common LO.
Figure 1

For example Ch0 can sink current from Ch2, but as all channels are configured in source mode then this is not correct working regime for the device, which can cause the damage of the channel.
This is an example why it is not recommended to create two bipolar channels.
The recommendation applies to all PXIe-414X SMUs.
 
 
 
 

Additional Information

In case where DUTs had different, isolated GNDs, so we have PXIe-4141 configured as shown in Figure 2, then this configuration is acceptable.
Figure 2
 
 

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