The OPAx863 include a rail-to-rail input stage. The main stage differential pair using PNP bipolar transistors operates for common-mode input voltages from V_S– – 0.2 V to V_S+ – 1.6 V. The amplifier inputs transition into the auxiliary stage using NPN transistors for common-mode input voltages from V_S+ – 1.6 V till V_S+ + 0.2 V. The PNP and NPN input stages offer a gain-bandwidth product of 50 MHz and a voltage noise density of 6.3 nV/√Hz. The offset voltage for the two input stages is matched to lie within the device specifications. The auxiliary NPN input stage does not use the slew-boost circuit during large-signal transient response. The input bias current for the PNP and NPN input stages is opposite in polarity, which adds an additional offset based on the values of the gain-setting and feedback resistors. A common-mode input voltage transition between these input stages causes a crossover distortion that must be considered in high-frequency applications requiring excellent linearity. Limit the common-mode input voltage to V_S+ – 1.6 V (maximum) for main-stage operation across process and ambient temperature.

The OPAx863 are bipolar amplifiers; therefore, the two inputs are protected with antiparallel back-to-back diodes between the inputs, which limits the maximum input differential voltage to 1 V. The amplifier is slew limited, and the two inputs are pulled apart up to 1 V when the antiparallel diodes begin to conduct in very fast input or output transient conditions. Make sure to use gain-setting and feedback resistors large enough to limit the current through these diodes in such conditions.