A Compact 40-GHz Doherty Power Amplifier With 21% PAE at 6-dB Power Back Off in 0.1- $\mu$ m GaAs pHEMT Process

This letter presents a monolithic 40-GHz Doherty power amplifier (PA) fabricated in 0.1-μm depletion mode (D-mode) gallium arsenide (GaAs) pseudomorphic high electron mobility transistor process. Different from most Doherty PAs, this PA occupies a compact chip size of 2.25 mm
²
because of the power-combining techniques. The measured results show a small signal gain of 12.7 dB, an output 1-dB compression point (OP
_{1 dB}
) of 19.2 dBm and saturated output power (P
_sat
) of 23.1 dBm at 40 GHz. Meanwhile, this PA achieves peak power added efficiency (PAE) of 28.5% and PAE of 21.1% at 6-dB power back off (PBO) from P
_sat
. Finally, the bandwidth of this well-improved backed-off efficiency is obtained from 39 to 41 GHz with an output third-order intercept point (OIP
₃
) of 20 dBm. Among published Ka-band GaAs Doherty PAs, this work exhibits the best 6-dB backed-off efficiency around 38 GHz, supporting the upper-frequency band for 5G wireless systems.