A 3.4-MHz Class-A Operational Amplifier in GaN Monolithic Technology with 80 dB Open-Loop Gain

Monolithic integration is essential to fully exploit the advantages of Gallium Nitride (GaN) technology, particularly its fast-switching capability. However, because of the significant limitations of this emerging technology, including the absence of p-channel transistors, realizing general-purpose building blocks like operational amplifiers (op-amps) remains challenging. This paper presents a two-stage op-amp with a Class-A output stage, implemented fully with n-channel transistors in STpGaN monolithic technology. The proposed design achieves a measured DC gain of 80 dB and a gain-bandwidth of 3.4 MHz for a capacitive load of 100 pF. Measured slew rates in unity-gain configuration are 1.8 V/μs (rising) and -0.2 V/μs (falling) for a 1 V input step. The measured PSRR is 63 dB at 10 kHz and 37 dB at 1 MHz. The op-amp occupies an area of 0.0889 mm2 and draws a quiescent current of 150 μA. A detailed comparison with the state-of-the-art is presented and discussed.