Video: Use a Source Measure Unit for “Crazy Stable” Measurements

Vektrex claims the SpikeSafe Source Measure Unit produces “crazy stable” measurements. In this video, we compare the voltage measurements of the Vektrex SpikeSafe SMU’s internal digitizer with those of the Keithley DMM7510 on the same load – paying close attention to the stability of the entire Vf pulse capture from each unit.

The load being used is a simple chip on board part with a max current of 2A and a forward voltage of about 20V.

First, we’ll start off by connecting to the SpikeSafe. And once it’s connected, we should see a section appear in the left-hand panel for the unit’s internal digitizer, which will be taking all our voltage measurements. Next, we’ll add the DMM Measure tab onto the Control Center by going to Tools > Add DMM Measure tab. We’ll then connect to the Keithley DMM7510, we should see the same Start Measure button appear once it’s successfully connected. As for our current source settings, we’ll go to Continuous Dynamic mode. Under Pulse Options: switch to Duty Cycle/Pulse Width and enter a duty cycle of 1% with a 500us pulse width. Compliance voltage will be 40V, and set current will remain at its default value of 100mA.

Under Digitizer Settings, we’ll change the capture mode to Capture Vf Full Pulse – all other settings have been auto-calculated. Same story on the DMM Measure tab, just change to Capture Vf Full Pulse mode.

Now we’re ready to capture some pulses. Let’s go back over to the Control Center and start the channel on the SpikeSafe. And while that’s running, we can click Start Measure on both the Digitizer and the DMM. The pulse captures will then appear in their respective tabs to the right. After the data have been plotted on the graphs, we can click stop on the SpikeSafe and begin analyzing the results.

To better compare the two plots, we’ll go to the graph settings panel for the Digitzer capture and scale the y-axis down to a minimum voltage of 20.5 and a maximum voltage of 21.5. We’ll do the same over on the DMM Measure tab. Now, switching between the two graphs, the oscillations in the Keithley data become really obvious. 

Vektrex SpikeSafe SMU
Keithley DMM7510

By comparison, the data from the SpikeSafe is almost entirely flat across the duration of the pulse, which is why we often hear how “crazy stable” the Vektrex SMU is. Hopefully, you’ll be saying the same from now on.

Learn more about the SpikeSafe SMU.