Differential amplifiers with enhanced gain and controlled common-mode output level

Differential amplifiers are provided with a common-mode controller that establishes an amplifier common-mode output level while it also enhances amplifier gain and output impedance. The amplifier includes cascode transistors and the controller includes positive-feedback transistors that respond to an output side of the cascode transistors and negative-feedback transistors that respond to an input side of the cascode transistors. Gain and output impedance are increased by the positive-feedback transistors and the increase is controlled by the negative-feedback transistors. Common-mode level is established by voltages between current and control terminals of the positive-feedback transistors. The differential amplifiers are shown to be especially suited for use in switched-capacitor structures.