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OPA858芯片放大倍数与带宽的问题

Other Parts Discussed in Thread: OPA858

我按照OPA858芯片推荐设计的跨阻放大电路,出现以下现象:

1.当反馈电阻为20K欧姆(无反馈电容),实测3dB带宽为102MHz;    -----芯片手册,Cin=2PF时,参考值为125MHz

2.当反馈电阻为100K欧姆(无反馈电容),实测3dB带宽为17MHz;;-----芯片手册,Cin=2PF时,参考值为60MHz

3.当反馈电阻为1M欧姆(无反馈电容),实测3dB带宽为1MHz;;      -----芯片手册,无参考

请问:由如图所示公式, 通过以上三个现象得出的Ctot不一样啊,这种现象正常吗?