Target Impedance
Two‐Port Shunt Thru Impedance Measurement
Description:
The two‐port shunt thru method allows the measurement of ultra‐low (uohms to ohms) impedance values. Limitations introduced due to the resistances of the ground braids of the two cables being in parallel with each other and in series with the DUT can be remedied by using a coaxial 50Ω common mode transformer or by using a semi‐floating or differential input.
This test measures the impedance of a 2mΩ resistor.
Demo Board: N/A
Setup File: 2mOhm wandwo J2102A.bode3
Two‐Port Shunt Thru Extended Impedance Measurement
Description:
This variation of the 2‐port shunt thru measurement extends the impedance range that the measurement can support. This extension is useful for measuring impedances that vary widely such as those encountered with opamps, low power voltage references, and linear regulators that span the 1‐port and 2‐port measurement ranges.
The extension process is simple. Here we add a 499 ohm resistor to each leg.
Demo Board: N/A
Setup File: 2‐port extended.bode3
LDO Output Impedance/Non-Invasive Stability
Description:
This test measures the output impedance and stability of an LDO using a 2 port probe and a common mode transformer. The 2‐port probe has two leads at the tip (joined with a special pointed clip) and a common ground port. While the connection of the tip and ground wire to the board may take some getting used to, this “browser” class probe is very useful in making multiple measurements in tight places without the need to recalibrate. A measurement of the VRTS1.5 board demonstrates this.
The extension process is simple. Here we add a 499 ohm resistor to each leg.
