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INA317: INA317仪表放大器前级加跟随器导致共模抑制比下降

Part Number: INA317

各位专家好:

请问在仪表放大器正极、负极同时增加相同规格的电压跟随器,为什么会导致共模抑制比的大幅度下降呢?

如果仅使用仪表放大器INA317,实测共模抑制比能达到110dB。而为了增加高输入阻抗和驱动能力,前级再添加一级电压跟随器,测试的结果是,共模抑制比大幅度下降,仅约80dB。

造成这种情况的原因是什么呢,能否解答一二?