ultrasonics receiver filter design

Dear all,

I am trying to design a filter for ultrasonics receiver. My schematics can be downloaded as shown. Before triggering the transducer, I probe the output from the first stage and the noise is nearly 40kHz which is the same as ultrasound. Then, after triggering the transducer, the output from the first stage is shown. Now i face with how to eliminate the 40kHz noise. Any suggustion about how to improve this schematics would be appreciated.

Just set your trigger level high enough over the noise floor that it doesn't trigger. Those scope shots show that your signal level is quiet high compard to the noise signal. You can't filter out 40khz noise from a 40kz signal a filter circuit can't tell the difference between noise and signal if the frequency is the same because there IS no difference.

Sceadwian, Thank you.
I guess when the ultrasonics receiver works, it generates such a 40kHz noise. The basic requirement of my project is not to generate such a 40KHz noise. How should I modify the schematics? The "+" of the receiver is connected to "IN" and the "-" of the receiver is connected to GND.

help me improve my schematics, dear all