A low-output-impedance fully differential op amp with large output swing and continuous-time common-mode feedback

A fully differential (zero common-mode voltage) op amp has been developed which has low output impedance, but unlike source-follower output stages, it has a large output swing, namely, 8 V_p-p for 1-kΩ load and a 5-V supply. The output stage, which is a combination of common-source and source-follower stages, is driven by the two complimentary outputs of the differential-output input stage. A continuous-time common-mode feedback circuit has been used, which due to the op amp´s low output impedance, causes negligible open-loop gain (95 dB) degradation. Floating compensation capacitors are used in order to reduce the capacitance value and, hence, the area (490 mil²)