HIGH-SWING OPERATIONAL AMPLIFIER OUTPUT STAGE USING ADAPTIVE BIASING

摘要

An output stage (123) includes two transistors (T3, T4) (switching transistor, and biasing transistor) coupled in series in a pullup current path between a VDDA node and an output node, (120) and also includes two transistors (Tl, T2) (switching transistor and biasing transistor) coupled in series in a pulldown current path between the output node (121) and a ground node. Providing the biasing transistors (T2,T4) reduces the maximum voltage dropped across the transistors, thereby allowing the transistors to have lower breakdown voltages than VDDA. An adaptive biasing circuit (26) adjusts the gate voltage on a biasing transistor (T2,T4) based on the output node (121) voltage. If the output voltage is in a midrange, then the gate voltage is set farther away from a rail voltage in order to reduce voltage stress. If the output voltage is in a range closer to the rail voltage, then the gate voltage is set closer to the rail voltage, thereby facilitating rail-to-rail output voltage swings.