Body Plot vs. Theory, Wien Bridge and Amplifier

[simply_me]

Hello,



I'm trying to design an ultrasonic range finder using only analog components. So far I've designed the Wien Bridge and one amplifier. The problem is that I'm trying to create a band-pass filter in the amp loop. While my calculations show that the filter's band is between 35.367-41.882kHz which is fine (I think ) since the incoming wave is ~38kHz, the bode plotter shows a different band:1-1MHz. Maybe one of my connections is wrong? Or the plotter is wrong? I'll be happy to hear any input you might have on the matter or how to improve the circuits.



Thank you,



A

 

[ericgibbs]

hi,
I assume R12 is disconnected in order to do the freq sweep/plot and your query is with the LM358 circuit on the right hand side of the drawing.?

 

[simply_me]

That is correct. I apologize, I should have made it more clear.

 

[ericgibbs]

That is correct. I apologize, I should have made it more clear.

hi,
OK, no problem.
I will run your circuit in the LTspice simulator, see what I get compared to yours, give me an half hour.

 

[simply_me]

Thank you.

 

[ericgibbs]

Thank you.

hi,
This what I get with the R12 connected and not connected.
Check my copy of your circuit for any errors.

 

[simply_me]

Thank you for running the simulations.
It looks much better when R12 isn't connected, but still the band width is way too high. I thought that R9 and C5 are the high pass filter and R11 and C4 are the low pass filter. This is strange....
On the simulation with R12 disconnected shouldnt C3 be removed too (from your circuit diagram)?

 

[ericgibbs]

Thank you for running the simulations.
It looks much better when R12 isn't connected, but still the band width is way too high. I thought that R9 and C5 are the high pass filter and R11 and C4 are the low pass filter. This is strange....
On the simulation with R12 disconnected shouldnt C3 be removed too (from your circuit diagram)?

hi,
On my circuit C3, is your C6, which you are showing as connected.?

 

[ericgibbs]

hi,
Look at this option, try it in your simulator.

If you want a sharper filter, consider two OPA stages.