A 4-mm-square 1.9 GHz Doherty power amplifier module for mobile terminals

A miniaturized Doherty power amplifier (PA) module for mobile terminals has been developed. Two GaAs HBTs and base bias circuits for a carrier amplifier and a peak amplifier are integrated onto a single chip GaAs MMIC (1.0 mm × 1.0 mm × 0.1 mm), which is mounted on a ceramic substrate (4.0 mm × 4.0 mm × 1.5 mm, alumina, dielectric constant = 8.8). In order to miniaturize the module size, a 25-Ohm environment is introduced in the module design, and two quarter-wave-length transmission lines are embedded inside the ceramic substrate. Measurement results indicate that a power-added efficiency (PAE) of 42% at 6 dB back-off, i.e. 22 dBm output power is obtained with the newly-developed Doherty PA. In other words, an improvement of 10% in PAE is achieved compared with the theoretical PAE of a conventional class B amplifier.