Steve Sandler: Sorry that didn’t work for you, but to be fair, I didn’t claim it would 😉. The J2113A is semi-floating which can cause offset errors without the grounds connected. It might work if you shorted 3 pins and left the CH2 signal pin open, but I haven’t tried it. There is another solution, but it costs a pretty penny. Literally, we’d like to measure an ideal SHORT, which of course doesn’t exist, and we can’t enter calibration parameters into the Bode 100, so the next best thing is an ideal-ish short. The P2100A-CAL board SHORT is about 200uOhms, so not low enough for ultra-low impedance. A penny is much thicker copper, so just a few uOhms, and it is large enough to achieve minimum, though non-zero, inductance. Try to use a clean penny so that you get good contact. Here are the steps.
First, with the P2102A probe and J2113A isolator connected in the traditional 2-port shunt-thru configuration, select the Shunt-Thru measurement from the Impedance Analysis tab and start a new measurement.
Figure 1 The Bode 100 measurement selection dialog. Select Shunt-Thru to perform the 2-port shunt-thru measurement.
Using the calibration board (P2100A-CAL) that comes with the P2102A probe, start a 2-port shunt-through measurement by setting the Source level to +13dBm, the Receiver 1 attenuator to 10dB, Receiver 2 attenuator to 20dB, and the Receiver bandwidth (RBW) to 30Hz, as shown below. You could set the Receiver bandwidth higher for the open and load calibrations, but it is easy to forget to reset it, so this really works best for me.
Figure 2 The Bode 100 dialog for configuring the AC sweep settings.
Perform the OPEN and LOAD calibrations using the calibration PCB or any other handy OPEN and LOAD calibrators. These are not critical for ultra-low impedance measurement.
Figure 3 The Bode 100 calibration dialog.
Reduce the Receiver 2 attenuator to 0dB.
Figure 4 Revised AC sweep dialog.
Place the probe on the penny and perform the SHORT calibration using the penny as the short.
Figure 5 Using a penny for the ideal-ish short.
After completing all three calibrations, you can start making measurements using the probe.
Figure 6 Calibration dialog after completing the three calibrations.
First, as a check, I measured the post calibration results while still on the isolation pads. The impedance floor should be about 20uOhms and a few pH.
Figure 7 Short measurement after calibration.
Next, I measured the P2100A-CAL SHORT pad, and you can see the low frequency ground loop effect is still present, though greatly reduced by the J2113A. The SHORT pad resistance is 200uOhms and the SHORT pad inductance is about 200pH for the 1206 probe head. Note that the low frequency ground loop effect is mostly gone, but it can be misleading. There is still an error, though reduced by the J2113A. Small changes in pin resistance will still show up here in the low frequency range.
Figure 8 Short measurement after calibration.
I also measured some parts whose impedance I have measured previously (a “known”). I typically use 1mOhm, 500uOhm, and 250uOhm resistors, whichever is closest to the DUT value I intend to measure.
Figure 9 1mOhm, 500uOhm, and 250uOhm sample measurements.
I also measured a mounted 1uF, 0805 chip capacitor. The capacitance measures 930nF and the ESL measures 236pH. This is very slightly lower than the manufacturer’s datasheet reports, but certainly within 100pH.
This method is not perfect, but it does offer a simple and reasonably accurate calibration method that supports measuring sub-milliohms and sub-nH using the P2102A probe with the Bode 100 VNA. For other analyzers, the full 2-port calibration is still recommended.