输出频率值何时为-3dB

如何在输出端获得-3dB的频率来编写测量表达式？
我在交流分析中运行这个模拟。
测量表达式我使用的是gainmax = max（out）;
这会返回最大输出值。
在3dB的频率我尝试使用find（）但它不会工作。



     以下为原文

  How to write the measurement expression in the way to get the frequency for -3dB at the output?
I run this simulation in ac analysis.
measurement expression I use is 
gainmax = max(out) ; this return the maximum values of output.

frequency at 3dB
i try to use find() but it wont work.

你真的需要实际的频率，或者这只是一个步骤，使用max（）函数来找到3dB带宽？
如果后者只使用bandwidth_func（）测量方程并一次搜索3dB带宽。
+此函数返回过滤器响应的带宽。
带宽定义为幅度响应低于最大幅度的DesiredValue dB的上下频率之间的差值。
它使用迭代过程来找到带宽限制响应的非理想响应的带宽。+它适用于高通，低通，带通和带阻滤波器，因此：bw3dB = bandwidth_func（db（out），3,2）应该适用于
你的榜样。



     以下为原文

  Do you really need the actual frequency or is this just a step, with the max() function, to find the 3dB bandwidth?

If the latter just use the bandwidth_func() measurement equation and search for the 3dB bandwidth in one go.

+This function returns the bandwidth of a filter response. Bandwidth is defined as the difference between the upper and lower frequency at which the amplitude response is DesiredValue dB below the maximum amplitude. It uses an iterative process to find the bandwidth on non-ideal responses for the band limited responses.+

It works for highpass, lowpass, bandpass and bandstop filters so:

bw3dB = bandwidth_func(db(out), 3, 2)

Should work for your example.