Operational amplifier and method for operating an operational amplifier

Operational amplifier, comprising:

• a symmetrical differential amplifier;
• a local common mode feedback circuit coupled to the symmetrical differential amplifier;
• a tail current source circuit comprising at least one first transistor and a second transistor and a current source resistor,
• wherein the tail current source circuit is configured to adjust a control voltage of the first transistor by using the second transistor such that a predetermined reference current flows through a load path of the first transistor, wherein a load path of the transistor is a path between a sink and a source of the transistor,
• wherein a control terminal of the second transistor is coupled to a sink terminal of the first transistor, and wherein a source terminal of the second transistor is coupled to the current source resistor,
• wherein the control voltage of the first transistor and a voltage applied across the current source resistor are correlated with each other;
• wherein a tail current of the symmetrical differential amplifier is based on a current flow through a load path of the second transistor and
• wherein the current flow through the load path of the second transistor is based on a current flow through the current source resistor,
• wherein the tail current source circuit comprises a third transistor between the current source resistor and the control terminal of the first transistor,
• wherein a source terminal of the first transistor and one end of the current source resistor are both connected to a ground of the operational amplifier, wherein a sink terminal of the second transistor is coupled to the symmetrical differential amplifier,
• wherein a sink terminal of the third transistor is coupled to the control terminal of the first transistor, a source terminal of the third transistor is coupled to the current source resistor and the source terminal of the second transistor, wherein the sink terminal of the third transistor receives a current flow originating from the same source as the reference current, and the source terminal of the second transistor, and a control terminal of the third transistor is coupled to the control terminal of the first transistor to counteract, in particular to reduce, a voltage drop across the current source resistor, wherein the local common mode feedback circuit comprises at least two resistors and the current source resistor is selected of a same type as the resistors of the local common mode feedback circuit, wherein of the same type means that the current source resistor comprises the same temperature coefficients and/or the same process variations and/or the same orientations in the geometrical configuration of the operational amplifier as the resistors of the local common mode feedback circuit.