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OPA847进行跨阻放大震荡,无法理解其中奥妙,求高人指点

Other Parts Discussed in Thread: OPA847

如图所示是使用OPA847进行跨阻放大的电路,在测试中发现跨阻放大在无光照情况下会输出一个500Mhz,300mV峰峰值的正弦波,按照官方手册计算公式这个跨组放大带宽在68Mhz左右,为啥有反馈电容还是震荡?后来去掉APD,将输入直接接地不震荡,将输入悬空继续震荡,后来将反馈电容去掉之后悬空和加上APD都不再震荡(测试时断开后级连接,直接测输出),这是什么原理?希望有人帮忙分析一下。