Class AB rail-to-rail input and output operational amplifier

An operational amplifier comprising:

• an input terminal;
• an input stage coupled to the input terminal of the operational amplifier, wherein the input stage is configured to couple to a control circuit and to a rail-to-rail output stage of the operational amplifier, wherein the input stage includes:
• a first differential input circuit coupled to the input terminal;
• a first current mirror coupled to the first differential input circuit;
• a second differential input circuit coupled to the input terminal;
• wherein, when the input terminal is at a positive voltage rail of the operational amplifier, the first differential input circuit is activated and the second differential input circuit is deactivated;
• wherein, in response to activating the first differential input circuit, the first current mirror is configured to provide a current of a predetermined value to each of a first input terminal and a second input terminal of the control circuit, and to each of a first node and a second node coupled to the rail-to-rail output stage of the operational amplifier;
• wherein, when the input terminal is at a negative voltage rail of the operational amplifier, the second differential input circuit is activated and the first differential input circuit is deactivated;
• wherein, in response to activating the second differential input circuit, the first current mirror is configured to provide a current of the predetermined value to each of the first and second input terminals of the control circuit, and to each of the first and second nodes coupled to the rail-to-rail output stage of the operational amplifier;
• wherein the input stage is configured to maintain the current provided to each of the first and second input terminals of the control circuit and to each of the first and second nodes coupled to the rail-to-rail output stage constant over the full input voltage range from the negative voltage rail to the positive voltage rail.

An operational amplifier comprising:

• a first input terminal;
• a second input terminal;
• an input stage coupled to the first and second input terminals of the operational amplifier, wherein the input stage is configured to couple to a control circuit and a rail-to- rail output stage of the operational amplifier, wherein the input stage includes:
• a first differential input circuit coupled to the first and second input terminals of the operational amplifier, wherein the first differential input circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor, wherein the gate terminal of the first and second transistors are coupled to the second input terminal of the operational amplifier, the drain terminal of the first transistor is coupled to the drain terminal of the second transistor, the source terminal of the first transistor is coupled to the source terminal of the second, third, and fourth transistors, and the gate terminal of the third and fourth transistors are coupled to the first input terminal of the operational amplifier;
• a first current mirror coupled to the first differential input circuit, wherein the first current mirror includes a fifth transistor, a sixth transistor, and a seventh transistor, wherein the drain terminal of the fifth transistor is coupled to the gate terminal of the fifth transistor and to the drain terminal of the first and second transistors, the gate terminal of the fifth transistor is coupled to the gate terminal of the sixth and seventh transistors, the source terminal of the fifth, sixth, and seventh transistors are coupled to a positive voltage rail of the operational amplifier, the drain terminal of the sixth transistor is coupled to the drain terminal of the third transistor and to a first input terminal of the control circuit of the operational amplifier, and the drain terminal of the seventh transistor is coupled to the drain terminal of the fourth transistor and to a second input terminal of the control circuit;
• and
• a folded cascode circuit coupled to the first current mirror, wherein the folded cascode circuit includes the sixth transistor, the seventh transistors, an eight transistor, a ninth transistor, a tenth transistor, an eleventh transistor, a twelfth transistor, and a thirteenth transistor, wherein the source terminal of the eight transistor is coupled to the drain terminal of the sixth transistor, the source terminal of the ninth transistor is coupled to the drain terminal of the seventh transistor, the drain terminal of the eighth transistor is coupled to a first input terminal of the rail-to-rail output stage of the operational amplifier and to the drain terminal of the tenth transistor, the drain terminal of the ninth transistor is coupled to a second input terminal of the rail-to-rail output stage and to the drain terminal of the eleventh transistor, the source terminal of the tenth transistor is coupled to the drain terminal of the twelfth transistor, the source terminal of the eleventh transistor is coupled to the drain terminal of the thirteenth transistor, and the source terminal of the twelfth and thirteenth transistors are coupled to a negative voltage rail of the operational amplifier.