Patent ID: 7554402

Claim:
An operational amplifier, comprising: an input stage, comprising: a differential transistor pair comprising first and second transistors, said pair biased with a tail current and arranged to receive a differential input signal at respective inputs and to conduct respective output currents in response; and at least one input stage bias current source, said input stage bias current sources providing respective bias currents for said input stage in response to a drive voltage, one of said bias currents being said tail current; a summing node at which at least some of said input stage bias currents are summed after flowing through said input stage, the current at said summing node being a current I sum ; and a feedback loop, comprising: a bias generator circuit arranged to receive I sum and to provide said drive voltage to said bias current sources such that I sum is maintained approximately constant; wherein said amplifier is powered by being connected between a supply voltage and a circuit common point, said bias generator including a means of providing a fixed voltage across a resistance R which is connected to conduct I sum between said summing node and said circuit common point such that I sum is maintained approximately constant.