Analysis and design of a stacked power amplifier with 196% fractional bandwidth using equivalent circuit model

Abstract

Stacked structure is a good solution to overcome the low output voltage swing provided by a single device. When several devices are stacked, the bandwidth and output power are multiple times higher. This article analyzes the small-signal voltage gain of the stacked structure, deriving the gain expression of the high-frequency model and simplified model. Based on the specific device parameter, the different small-signal voltage gains between the two models are compared and the designed stacked structure is proved to obtain a flat gain at low frequencies below about 3 GHz. To our best knowledge, this is the first article to analyze the gain flatness of stacked structure with two equivalent circuit models. To verify the stacked theory, a pseudomorphic high-electron-mobility transistor（PHEMT） power amplifier (PA) is implemented using 0.25 μm Gallium arsenide (GaAs) technology. The PA achieves an ultra-high bandwidth of 30 MHz to 3 GHz and a linear gain of 21 dB ± 1.5 dB. At a 16-V drain bias voltage, a saturated output power of higher than 2 W and a peak power-added efficiency (PAE) of 44.1% are attained.