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.