Please tell me how to calculate this filter circuit

littleshrimp

Please tell me how to calculate this filter circuit [Copy link]

This is an ultrasonic ranging reference circuit from ADI

The ultrasonic frequency is 40KHz

The first question is, for example, the cutoff frequency of the high-pass filter composed of C10 and R6 is 41317Hz, and the cutoff frequency of the low-pass filter composed of C13 and R4 is 36860Hz

I don't understand why the high-pass cutoff frequency is set to be greater than 40KHz, while the low-pass cutoff frequency is set to be less than 40KHz?

The second question is how is the gain of 132 or 42.4dB calculated?

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