Design of an Enhanced Rail-to-Rail Power Operational Amplifier for Photovoltaic MPPT Application

This paper presents a high-voltage rail-to-rail power operational amplifier designed in SMIC 180nm BCD (Bipolar-CMOS-DMOS) technology for photovoltaic MPPT applications. The input stage employs transistors operating in strong inversion region, with rail-to-rail input capability achieved through optimized tail current distribution across different voltage domains to maintain constant input transconductance(gm). A gain-boosting architecture is implemented to enhance the amplifier's DC gain, thereby improving precision. The output stage features a class-AB feedforward configuration that enables rail-to-rail output swing while increasing maximum output current capability. The simulation results demonstrate that the operational amplifier operates over a supply voltage range of ±4 V to ±28.5 V, with an input offset current below 100 nA. Under unity-gain configuration, the amplifier achieves a low-frequency gain of 137.64 dB with a phase margin of 57.7°, while maintaining transconductance variation (Agm) below 6%. When subjected to a 12 V input step with 100 pF load capacitance, the positive and negative slew rates are measured at 23.5 V/μs and 14 V/μs respectively.