Selected topics in RF coplanar probing

The RF coplanar probe is a popular tool for launching high-frequency signals onto and off of a wafer. Physically contacting the die, it establishes a crucial link between the test system and wafer. Their proper use permits a higher degree of measurement accuracy compared to test fixturing. To augment the reader's understanding, this tutorial reviews selected issues related to the design, construction, characterization, selection, calibration, and repeatability of RF on-wafer coplanar probes.

I. Introduction

While THE digital signal processing (DSP) section of a wireless handset holds thousands of transistors, the biggest challenge in a wireless handset design is often the RF section. The problem usually cited is a lack of computer-aided design (CAD) models to accurately predict the RF integrated circuit's (RFIC) performance [1]. When an RF problem occurs in the design, it is usually attributed to the CAD model, its theoretical basis being drawn into question. Yet shortcomings in the RF performance of a die are just as easily due to the RF measurements used to generate the models as to the models themselves. Recently, RF on-wafer probing has extended beyond RFICs into the world of high-speed digital integrated circuits (ICs) where clocks speeds have exceeded 1 GHz. These trends in digital and RFICs emphasize the need for reliable on-wafer RF measurements.