Direct -Field Measurement and Imaging of Oscillations Within Power Amplifiers

• Published in: IEEE transactions on instrumentation and measurement 2019-08, Vol.68 (8), p.2971-2978
• Main Authors: Urbonas, Jonas, Kim, Kevin, Aaen, Peter H.
• Format: Article
• Language: English
• Subjects: Bifurcation detection; device characterization; Electric fields; Electron mobility; electrooptic (EO) sampling; High electron mobility transistors; Inspection; laterally diffused metal–oxide–semiconductor (LDMOS) transistor; Microwave measurement; near-field measurement; Network analysers; Nonlinear analysis; oscillation; Oscillators; PHEMTs; Power amplifiers; Power measurement; Radio frequency; Raster scanning; Semiconductor device measurement; Semiconductor devices; Spatial resolution; stability; Stability analysis; Transistors
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2018.2869407

We present, for the first time, a measurement system that is capable of directly detecting and identifying the physical location of an oscillation within radio frequency (RF) and microwave power amplifiers (PAs). The method uses a combined external electrooptic, nonlinear vector network analyzer, and vector load-pull measurement system, which allows the measurement of cross-frequency phase-coherent multiharmonic vector electric fields ( {E} -fields) above the transistor with an 8- \mu \text{m} spatial resolution and 20 MHz-40 GHz bandwidth. Raster scans above the amplifier allow the time-domain {E} -fields to be animated and superimposed on top of the amplifier image, enabling immediate identification of any oscillations by direct inspection. The method is first demonstrated on a low-power PA composed of two parallel 0.1-W pseudomorphic high electron mobility transistors that is intentionally designed to have an odd-mode oscillation. The applicability of the method is further demonstrated by measuring and animating in-package parametric odd-mode oscillations within a 260-W laterally diffused metal-oxide-semiconductor transistor operating at 2.2 GHz under pulsed RF conditions with 10- \mu \text{s} pulses and 10% duty cycle. The measurement and identification technique are applicable to all semiconductor devices as the external {E} -field is noninvasively measured above the amplifier.