Abstract
We present for the first time a measurement system that is capable of directly detecting and identifying the physical location of an oscillation within RF and microwave power amplifiers. The method uses a combined external electrooptic, non-linear vector network analyzer, and vector load-pull measurement system, which allows the measurement of crossfrequency phase-coherent multi-harmonic vector electric fields above the transistor with an 8 μm spatial resolution and 20 MHz – 40 GHz bandwidth. Raster scans above the amplifier allow the time-domain electric 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 amplifier composed of two parallel 0.1-W pHEMT 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 (LDMOS) transistor operating at 2.2 GHz under pulsed RF conditions with 10 μs pulses and 10% duty cycle. The measurement and identification technique is applicable to all semiconductor devices as the external electric field is non-invasively measured above the amplifier.