Design of Two-Stage MOSFET-Only Operational Amplifiers

In this work, the gate-to-bulk capacitance property of MOS transistors is employed to design high-speed two-stage operational amplifiers (opamp). Traditional design of two-stage opamps recommends MIM or PIP capacitors to avoid instability in closed-loop applications. In addition to area efficiency achieved by replacing these capacitors with MOS transistors, the integration of the opamp would become compatible with standard digital CMOS technologies. Circuit-level simulation compares two opamps that are designed to be employed in a 50MS/s switched-capacitor sample-and-hold circuit. For the same specifications in 0.18 mu m CMOS technology, the proposed MOSFET-only opamp is about 52% smaller than a conventionally design when neglecting the signal path capacitors.