Fully-Integrated Broadband GaAs MMIC Load Modulated Balanced Amplifier for Sub-6 GHz Applications

In this brief, a monolithically integrated broadband load modulated balanced amplifier (LMBA) chip without BA pre-matching network is proposed and designed. It is the first time that integrated LMBA operating at sub-6 GHz has been discussed about broadband performance. BA follows with only one inductor and output quadrature coupler, which can effectively reduce loss and improve efficiency. The load modulation behavior of BA is analyzed, indicating that it has an appropriate modulation trajectory. For verification, a LMBA chip was fabricated and measured in the 0.25- $\mu {\mathrm{ m}}$ GaAs pHEMT process. Continuous-wave measurements demonstrate a saturated output power of 30.2–31.8 dBm with drain efficiency (DE) of 34.3–59.2%, and 6-dB back-off DE of 27.7–40.4% in 4.2–5.2 GHz. Modulated signal measurements prove that the linearity of LMBA can be calibrated by digital predistortion.