Enhancement of Linearity and Flatness in Broadband Power Amplifiers via Baseband Impedance Optimization

ABSTRACT Broadband power amplifiers (PAs) not only demand high efficiency and linearity but also face stringent challenges regarding the flatness of their gain and efficiency; the nonideality of baseband impedance is a key factor that leads to nonlinear distortion and dynamic performance fluctuations, impacting the PA's performance flatness. In this paper, a passive multibranch baseband impedance control unit (BICU) is proposed to provide a low and flat controllable impedance over the wide baseband frequency range of 1–600 MHz, and a broadband PA incorporating this BICU is designed and tested. Experimental results demonstrate that introducing the BICU in the 1.8–2.4 GHz range effectively stabilizes the baseband impedance, significantly improving the flatness of the power‐added efficiency (PAE), which remains relatively stable at around 62% with reduced fluctuations across the operating band. Simultaneously, at an output power of approximately 38 dBm, the third‐order intermodulation distortion (IMD3) improved by about 3–5 dBc, exhibiting significantly suppressed sideband asymmetry, thus enhancing linearity, whereas the gain was maintained at around 12 dB. This research validates the feasibility of improving the linearity, efficiency flatness, and overall performance flatness of broadband PA by optimizing the baseband impedance.