Agilent 5989-5935EN Ultra-Low Impedance Measurements using 2-Port Measurements c20140811 [52] free download

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Keysight Technologies Ultra-Low Impedance Measurements Using 2-Port Measurements Application Note Introduction In this application note, a 2-port network analyzer is used to measure impedances well below 1 Ohm. This regime is difficult to measure in practice with a conventional 1-port VNA due to real world limitations of signal to noise ratio and fixturing reproducibility. With this new technique of using 2-ports and a conventional network analyzer, impedances as low as 1 milliOhm and inductances in the pH range can be routinely measured. This type of measurement is critically important for all the components that make up the power distribution network system. Table of Contents Introduction ... Cover Limitations of 1-Port VNA Impedance Techniques ... 04 4-Point Kelvin Technique for Ultra Low DC Resistance Measurements ... 08 2-Port Measurements Reduces Fixturing Parasitics ... 10 Measurement Examples Using the Two-Port Measurement Technique ... 14 The Power Distribution Network (PDN) ... 19 Decoupling Capacitors ... 33 Planes and Capacitors ... 39 How to Set Up a Measurement System... 41 Conclusion ... 50 03 Why is low impedance important? Most interconnects used to transport signals have impedances in the 50 to 100 Ohm range. This is in the perfect range for measurement by conventional network analyzers with port impedances of 50 Ohms. But, for structures with ultra-low impedances, the mismatch with the 50 Ohm source impedance means that nearly all of the signal will reflect, and distinguishing 0.1 Ohm from 0.01 Ohms becomes extremely difficult. It is predominately in the power distribution network (PDN), the interconnects from the voltage regulating module (VRM) that generates the precisely regulated voltage to the pads on the chip for the Vcc or Vdd rails, where ultra low imped- ance values are required. It is not uncommon in microprocessor based systems to have a target impedance for the entire PDN of less tha