Fully differential folded cascode CMOS operational amplifier having adaptive biasing and common mode feedback circuits

An adaptive bias circuit, in response to a first input voltage and a second input voltage, for providing four output currents, which comprises:

• an operational transconductance amplifier for providing a first and a second currents in response to the first input voltage and the second input voltage, respectively;
• a first subtractor circuit for adding a current to the first and the second currents, respectively, in case the first current is larger than the second current;
• a second subtractor circuit for adding a current to the first and the second currents, respectively, in case the second current is larger than the first current;
• and
• four output transistors, each of which provides one of the four output currents, wherein the four output currents include a first output current which is proportional to the first current and of a same sign with the first current;
• a second output current which is proportional to the first current and of an opposite sign with the first current;
• a third output current which is proportional to the second current and of a same sign with the second current;
• and a fourth output current which is proportional to the second current and of an opposite sign with the second current.