Operational amplifier of class AB

A class AB operational amplifier comprising:

• a first input transistor coupled between a first internal node and a first common node, and having a control terminal coupled to a first differential input terminal;
• a second input transistor coupled between a second internal node and the first common node, and having a control terminal coupled to a second differential input terminal;
• a first input stage load transistor diode connected and coupled between a first voltage reference and the first internal node;
• a second input stage load transistor diode connected and coupled between the first voltage reference and the second internal node;
• first and second output transistors coupled in series between the first voltage reference and a second voltage reference, an interconnection node of the first and second output transistors being an output terminal of the operational amplifier, and the first output transistor having a control terminal connected to a control terminal of the second input stage load transistor;
• a tail current generator coupled between the first common node and the second voltage reference;
• an adaptive bias block coupled between the first and second voltage references, the adaptive bias block being coupled to the first common node;
• and
• a positive feedback network coupled between the first voltage reference and the first and second internal nodes,
• wherein the adaptive bias block comprises one or more circuits that each include a current subtractor and a mirror block coupled in series between the first and second voltage references, and
• the current subtractor comprises:
• first and second additional transistors having their control terminals connected together and to the mirror block, and having their first conductive terminals connected together and to the second voltage reference, the first additional transistor having a second conductive terminal connected to its control terminal and to the mirror block, and the second additional transistor having a second conductive terminal connected to the mirror block;
• and
• third and fourth additional transistors having their control terminals connected together and to the second control terminal of the second additional transistor, and having their first conductive terminals connected together and to the second voltage reference, the third additional transistor having a second conductive terminal connected to its control terminal and to the mirror block, and the fourth additional transistor having a second conductive terminal connected to the first common node.

A class AB operational amplifier comprising:

• a first input transistor coupled between a first internal node and a first common node, and having a control terminal coupled to a first differential input terminal;
• a second input transistor coupled between a second internal node and the first common node, and having a control terminal coupled to a second differential input terminal;
• a first input stage load transistor diode connected and coupled between a first voltage reference and the first internal node;
• a second input stage load transistor diode connected and coupled between the first voltage reference and the second internal node;
• first and second output transistors coupled in series between the first voltage reference and a second voltage reference, an interconnection node of the first and second output transistors being an output terminal of the operational amplifier, and the first output transistor having a control terminal connected to a control terminal of the second input stage load transistor;
• a tail current generator coupled between the first common node and the second voltage reference;
• an adaptive bias block coupled between the first and second voltage references, the adaptive bias block being coupled to the first common node;
• and
• a positive feedback network coupled between the first voltage reference and the first and second internal nodes,
• wherein the adaptive bias block comprises first and second circuits that each include a current subtractor and a mirror block coupled in series between the first and second voltage references.

An integrated circuit including at least one class AB operational amplifier, the operational amplifier comprising:

• a first input transistor coupled between a first internal node and a first common node, and having a control terminal coupled to a first differential input terminal;
• a second input transistor coupled between a second internal node and the first common node, and having a control terminal coupled to a second differential input terminal;
• a first input stage load transistor diode connected and coupled between a first voltage reference and the first internal node;
• a second input stage load transistor diode connected and coupled between the first voltage reference and the second internal node;
• first and second output transistors coupled in series between the first voltage reference and a second voltage reference, an interconnection node of the first and second output transistors being an output terminal of the operational amplifier, and the first output transistor having a control terminal connected to a control terminal of the second input stage load transistor;
• a tail current generator coupled between the first common node and the second voltage reference;
• an adaptive bias block coupled between the first and second voltage references, the adaptive bias block being coupled to the first common node;
• and
• a positive feedback network coupled between the first voltage reference and the first and second internal nodes,
• wherein the adaptive bias block comprises one or more circuits that each include a current subtractor that determines a difference between a current at the first internal node and a current at the second internal node and generates a boost current that is proportional to this difference.