Impact of Second Harmonic Source Impedance on the Linearity Performance of Hybrid Inverse Continuous Modes

This letter analyzes the impact of second harmonic source impedance on the linearity performance of Hybrid Inverse Continuous Modes (HICMs). The study reveals that the linearity of the HICM mode deteriorates significantly when the second harmonic source impedance falls within a small region where the input nonlinearity parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma ~\lt 0$ </tex-math></inline-formula>. Outside of this specific area, HICM linearity remains nearly constant across the rest of the Smith chart. This finding is crucial for designers to prevent unexpected linearity degradation when expanding the second harmonic source impedance space in HICM. Experimental verification involves implementing input harmonic control to prevent the second harmonic source impedance from operating in regions with degraded performance, thereby achieving both good efficiency and linearity. A power amplifier (PA) with a frequency range of 1.7–2.8 GHz is designed based on the CGH40010F. The test results show that the drain efficiency is 62.0%–71.9%, and the output power is 40.6–42.8 dBm. The linearity is tested with a 100 MHz 5G NR signal (with a peak-to-average power ratio of 8 dB) at 2.35 GHz. The worst adjacent channel power ratio (ACPR) is −33.6 dBc without digital predistortion (DPD), and −49.2 dBc with DPD. Around 34.35 dBm average output power (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {ave}}$ </tex-math></inline-formula>) and 34.6% average DE (DE<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {ave}}$ </tex-math></inline-formula>) were obtained. When the output power is at the backed off by 3 dB, the measured IMD3 is less than −30 dBc.