Noise Source Impedance Measurement in SMPS

Abstract

An accurate measurement method to extract common mode (CM) and differential mode (DM) noise source impedances of a switched-mode power supply (SMPS) under operating condition is presented in this chapter. With a proper pre-measurement calibration process, the proposed method allows extraction of both the CM and the DM noise source impedances with very good accuracy. These noise source impedances come in handy to systematically design an electromagnetic interference filter for a SMPS with minimum hassle.

Keywords: Calibration process, CM noise source impedance, Common mode chokes, Common mode inductors, Conducted Electromagnetic Interferences, Conducted emissions, Coupling capacitors, Differential mode chokes, Differential mode inductors, Differential mode noise impedance, Direct clamping two-probe approach, DM noise source impedance, Equivalent series inductance (ESL), Equivalent series resistance (ESR), Hilbert transform, Insertion Loss (IL), Linearization, Load termination impedances, Mutual inductance, Noise coupling mechanism, Noise source impedance measurement, Noise source impedances, Noise termination impedances, Parasitic capacitances, Parasitic inductances, Power line impedances, Reflection coefficient, Reverse-recovery phenomena, RF instruments, RF isolation, Scattering parameters, Sensing probe, Small-signal perturbation, S-parameters, Switched-mode power supplies (SMPS), Vector Network Analyser (VNA), Y-capacitors (Y-caps), X-capacitors (X-caps)