I've designed a 4th order lowpass filter using filterPro. when i simulated the circuit using OrCad i don't get the expected lowpass filter transfer function. I used AC sweep for analysis with start frequency of 1Hz, end frequency of 650Hz and total points of 10. the output just gives me 0. see the attached circuitView attachment lowpass filter.bmpView attachment lowpass filter.bmp
First try it from 1 Hz to 100 MHz, with 100 points per decade.
Note that if the frequency response plot is showing 0 dB, then that means the output is the same amplitude as the input. And so maybe you are not yet looking in the correct frequency range and have not seen the cutoff region.
I've tried simulating with the values you mentioned, the response is still not correct. Do i have to change other settings in OrCad besides those that i mentioned?
I don't know if you mean the supply for the opamp (LM324 from OrCAD) or you mean the supply for the entire circuit. if you're talking about the supply voltages for LM324, i used VDC with amplitude of 15V (both positive), i figured out that LM324 has both +/- open. so i connected my 15V on both +/-
I don't know if you mean the supply for the opamp (LM324 from OrCAD) or you mean the supply for the entire circuit. if you're talking about the supply voltages for LM324, i used VDC with amplitude of 15V (both positive), i figured out that LM324 has both +/- open. so i connected my 15V on both +/-
And I don`t know what you mean with "entire circuit"? I think, the opamp is the only part that must be powered, is it not?
More than that - VDC with an "amplitude"?
And what is the meaning of the last sentence ("LM324 has both +/- open. so i connected my 15V on both +/-") ?
(I can see the dc supply symbols but not the corresponding values: Are they +-15 Volt?)