Direct ${E}$ -Field Measurement and Imaging of Oscillations Within Power Amplifiers

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-μm 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-μs 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.