A 5.15–7.125-GHz Differential Power Amplifier With Enhanced Linearity of Average Power Region Using Dynamic Cross-Coupled Capacitor

This article presents a 5.15–7.125-GHz differential power amplifier (PA) with enhanced linear output power by dynamic cross-coupled capacitors (
$C_{\text {cc}}$
) for both fifth-generation new radio-unlicensed (5G NR-U) and 802.11ax wireless local area network (WLAN) applications. The proposed dynamic
$C_{\text {cc}}$
compensates for nonlinear parameters of transistors and leads to improved linearity in the average output power region. The multicoupled four-way transformer (TF) is also proposed for a high symmetry combining structure to reduce the imbalance of differential PA and for a 30% fractional bandwidth of optimal output matching with a low turn ratio and low insertion losses to implement on a nine-layer printed circuit board applications. The proposed differential PA is implemented in a 2-
$\mu \text {m}$
InGaP/GaAs heterojunction bipolar transistor (HBT) process. The PA achieves a gain of 24 dB, a saturated output power of 33.1 dBm, and a power added efficiency (PAE) of 40.4% with a collector voltage of 5.5 V over 5.15–7.125 GHz under a continuous wave (CW) signal. The linearity of the proposed PA is further evaluated with various modulation signal schemes to validate its suitability for NR-U and WLAN applications. The PA with NR 100-MHz cyclic prefix (CP) and discrete Fourier transform (DFT) signal having a peak-to-average power ratio (PAPR) of 11.4 and 8 dB achieves linear output power meeting −33 dBc of 24.6 and 27 dBm and PAE of 10% and 16.3% in NR evolved universal terrestrial radio access (E-UTRA) adjacent channel leakage ratio (ACLR) condition. The PA also achieves the output power of 19.8 dBm with a PAE of 4.3% (error vector magnitude (EVM) = −40 dB) under 802.11ax MCS11 80 MHz having a PAPR of 10.7 dB.