Class-D⁻¹ Power Amplifier Using Cavity Filtering Balun for All-Digital RF Transmitters

This letter presents a novel Class- $\text{D}^{-1}$ power amplifier (PA) based on a dielectric filled cavity balun. Different from the conventional Class-D PA, the functions of signal combination, filtering, and output impedance matching are all integrated into the high $Q$ filtering balun. This method not only provides a high efficiency and sharp roll-off for noise shaping but also reduces the design complexity. The effect of $C_{\mathrm {ds}}$ on efficiency is also analyzed. A simple neutralizing network is used to obtain additional efficiency enhancement. For demonstration, a filtering Class- $\text{D}^{-1}$ PA operating at 1.82 GHz is fabricated and measured. With the measured result, the proposed PA shows an output power of 41 dBm and a drain efficiency of 71.8% with a high-frequency selectivity.