Calibration method for coupler based time domain waveform measurements

This paper addresses the issues related probing radio frequency (RF) waveforms in nonlinear circuits. Having access to time domain waveforms is essential when developing nonlinear circuits. However, in many cases these signals are not easy accessible which urge the need for some kind of coupler integrated onto the printed circuit board (PCB). Defined mostly by spatial circuit constrains these couplers usually perform suboptimal and in addition also the measuring instrument may add distortion. This paper describes a methodology that tackles all these issues by a compact two stage calibration approach. It allows to pre-characterize a coupler in conjunctions with the oscilloscope in a way that time domain waveforms can be measured directly in a circuit at a well defined reference plane.