Internal all-differential operational amplifier for CMOS integrated circuits

An internal all-differential operational amplifier for integrated circuits of the CMOS type, comprising two CMOS cascode circuits, identical to each other, each having a first and a second transistors with a channel having a first polarity and a third and fourth transistors with a channel having the opposite polarity, the drain of the first transistor being connected to the source of the second transistor, the drain of the fourth transistor being connected to the source of the third transistor, the drains of the second and of the third transistor being connected to each other and forming one of the output terminals of said amplifier, the sources of the first transistors of the two cascode circuits being both connected to the drain of a fifth transistor having said first polarity, the source of which is fed by a first supply voltage, and the sources of the fourth transistors of the two cascode circuits being fed by a second supply voltage, the two input signals being applied, by means of capacitor and switching means simulating input resistors, to the respective gates of said two first transistors, the other three gates of each cascode circuit being biased by respective fixed biasing voltages, the gate of the fifth transistor being biased by a dedicated fixed biasing voltage by means of capacitor and switching means constituting a common-mode feedback circuit.