Operational amplifier compensation circuit for preventing phase reversal and maintaining performance for inputs outside the common mode range

An input circuit for an operational amplifier, comprising:

• a pair of differentially connected transistors that have respective current and control circuits and are connected to receive respective differential inputs, said differential transistors responding to a particular input by producing a forward-biased parasitic diode in one of said differential transistors;
• a folded cascode pair of transistors that have respective current and control circuits, and are coupled to said differential transistors;
• a pair of resistors connected between a reference potential and the current circuits of the differential and cascode transistors to produce resistor voltages that control the currents flowing through said cascode transistors' current circuits;
• a phase compensation circuit that responds to the particular input by shifting the resistor voltage for the other differential transistor to prevent a phase reversal of the resistor voltages;
• and
• a current compensation circuit that responds to the particular input by shifting the cascode transistors' base-emitter voltages to limit the magnitudes of said cascode transistors' circuit currents to a range within which the operational amplifier does not latch up.