Patent ID: 7298210

Claim:
An operational amplifier comprising: (a) a first stage including differential-pair-coupled first and second input transistors and a controlled active load circuit; (b) a second stage including differential-pair-coupled third and fourth input transistors and a load circuit, a first output of the first stage being coupled to a first input of the second stage, a second output of the first stage being coupled to a second input of the second stage; and (c) a common mode feedback amplifier having a first input coupled to receive a common mode signal from the second stage for producing an amplified common mode signal on a control input of the controlled active load circuit, so as to provide fast settling of an output of the second stage without substantially increasing amplifier noise, wherein the controlled active load circuit of the first stage includes first and second active load transistors each having a control electrode coupled to receive the amplified common mode signal, and wherein the first stage includes a first current mirror including a first diode-connected transistor having a control electrode coupled to a first electrode of the first active load transistor and to a control electrode of a first current mirror output transistor, a second electrode of the first current mirror output transistor being coupled to the control electrodes of the first and second active load transistors, and wherein the first stage also includes a second current mirror including a second diode-connected transistor having a control electrode coupled to a first electrode of the second active load transistor and to a control electrode of a second current mirror output transistor, a second electrode of the second current mirror output transistor being coupled to the control electrodes of the first and second active load transistors, to contribute to compensation of a common mode feedback loop of the amplifier.