How to Measure Ultra Low Impedance (100uOhm and lower) PDNs
(Room 204)
17 Oct 18
9:00 AM
-
11:15 AM
Who should attend? All engineers that may be facing 100uOhm PDN’s now or in the near future, or those that just have an interest learning new measurement techniques. Measuring ultra-low impedance is a common requirement for assuring power integrity. This meant measuring 1 milliOhm to 2 milliOhm voltage regulator modules (VRM’s) and power distribution networks or (PDN’s). Every year we talked about how operating voltages are falling and frequency is increasing. Maybe some of us realized this meant higher operating current and therefore lower impedance. Today, it is common to see 500uOhm power rails, but more recently the bleeding edge is below 100uOhms. Measuring 100uOhms is a significant challenge, even using the venerable 2-port shunt-thru measurement that has served as the staple of ultra-low impedance measurement. The dynamic range of the 100uOhm, 2-port, measurement is 108dB. An impedance dip to 30uOhms reduces this to 118dB. This dynamic range presses the limits of the noise floor for even the best VNA. The addition of operating voltage noise, including ripple and load-induced transients increases the challenge. At these ultra-low impedance levels everything matters, from the quality of the instrument interconnects, to the quality of the ground loop isolator. In this tutorial, you’ll learn some techniques that will improve the accuracy and fidelity of your sub 100uOhm measurements. You’ll learn the pros and cons of the 2-port vs 3-port measurement technique. With a little bit of luck, we’ll demonstrate a 100uOhm impedance measurement as well as showing some measurements highlight the challenges you’ll face along the way. Key Takeaways: • Ultra-low impedance measurement basics • Choosing between 2-port and 3-port measurement techniques • Dealing with measurement ground loops • The importance of interconnects and signal to noise ratio • Self-impedance vs Transfer impedance • Measuring something you know (close to 100uOhms)