robotron Posted February 14, 2011 Report Share Posted February 14, 2011 Hello. Have you ever seen this kind of opamps? i dont even know what this circuit does, not even one of the two opamps... Where's the power input of the second? ANd in the first one, ewhats going on with connecting the power input with the opamps input??? If anyone has even a slight clue, please comment. For gods sake there is feedback in feedback, the second's fdeedback is connected in the first's feedback. What i know this curcuit does is amplify some certain frequencies, only that. Please help Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 14, 2011 Report Share Posted February 14, 2011 The opamps have a single-polarity supply so they are biased at half the supply voltage with R3, R4 and R10. R2 is usually not needed. Since the opamps are DC-coupled then only the first opamp is biased and it biases the second opamp.The first opamp is a follower that has a very low output impedance needed as the source by the second-order high-pass Sallen and Key filter that is the second opamp.I think R5 is supposed to connect to the bias voltage instead of the output of the first opamp like this: Quote Link to comment Share on other sites More sharing options...
robotron Posted February 15, 2011 Author Report Share Posted February 15, 2011 i understood some stuff and thanks for that. i couldnt simulate it on TINA. i understood the sallen key filter and i tried on tina to see that with my own eyes, the thing that if you use single bias polarity to the opamp you will get half the output voltage. i tried but with two points polarity i got outcome about 5V, with two points symmetric polaity only 6.5 volts. whats going on???btw YOU JUST TOTALLY SAVED MY ASS ON THE RIGHT TIME WITH IT!!! it was for a colleg paper we had to create board (pcb), then say one thing or two about the circuit. btw, what does the first opamp do?again thakns Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 15, 2011 Report Share Posted February 15, 2011 The Sallen and Key highpass filter needs to be driven from a very low impedance. The output of the first opamp is a very low impedance.R5 in your sketch appears to be in the wrong location which might explain why TINA doesn't work with it. Quote Link to comment Share on other sites More sharing options...
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