Clamping circuit for operational amplifiers

An operational amplifier having output voltage limitation, comprising:

• first and second transistors configured as a differential input of an operational amplifier;
• a first current source coupled to the first and second transistors;
• a current mirror coupled to the first and second transistors;
• a third transistor adapted as an output stage of the operational amplifier, the third transistor coupled to the current mirror and the second transistor;
• a second current source;
• a fourth transistor coupled to the second current source and a clamp voltage reference;
• and
• a fifth transistor coupled to the second current source and the current mirror, wherein when a voltage at the output of the operational amplifier is substantially equal to the clamp voltage reference the fifth transistor substantially controls the third transistor so that the output of the operational amplifier does not substantially exceed the clamp voltage reference.

A method of limiting an output voltage of an operational amplifier, said method comprising the steps of:

• providing a differential input transistor pair in an operational amplifier having an output, wherein the differential input transistor pair controls the output;
• providing a voltage clamp differential transistor pair;
• and
• coupling one transistor of the voltage clamp differential transistor pair to a clamp voltage reference, and the other transistor of the voltage clamp differential transistor pair to the operational amplifier output such that when the output of the operational amplifier has a voltage substantially equal to the clamp voltage reference, the other transistor of the voltage clamp differential transistor pair controls the output so that the voltage on the output does not exceed the clamp voltage reference,
• wherein when the other transistor of the voltage clamp differential transistor pair controls the output the differential input transistor pair does not control the output.