Common-Mode Response Overlapping vs. Shaping in Rail-to-Rail Op-Amp Input Stages

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In this paper, a circuit technique—common-mode (CM) response overlapping—for maintaining the small-signal behavior of rail-to-rail amplifiers nearly constant over the whole input CM range, is introduced. This technique modifies the CM response of the rail-to-rail input stage adequately by means of two constant input floating voltage sources, which are adjusted by using a static tuning section. Its performance is compared with a second technique—CM response shaping—, which is also based on two variable input floating voltage sources, but relies on a dynamic feedback tuning loop. Experimental results obtained from two 3-V 0.8-μm CMOS single-stage rail-to-rail amplifiers, which operate with CM response overlapping and shaping, respectively, are provided.

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