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How to Create a Band Pass Filter Using an Operational Amplifier

A filter lets certain frequencies of a signal pass through while muting others. The three main filter types are low pass, high pass and band pass. A low pass filter allows low frequencies to pass through, muting frequencies above the cutoff, while a high filter passes high frequencies while cutting those below the cutoff. A band pass filter is the combination of these two filter types. Operational amplifiers, or op-amps, are integrated component chips that you can use in conjunction with resistors and capacitors to make active filter circuits.

Things You'll Need

Op-amp
2 resistors
2 capacitors
Wire
Soldering iron
Solder

Instructions

- 1
  Connect capacitor one with the source of the signal you wish to filter.
- 2
  Connect resistor one to capacitor one.
- 3
  Connect the other end of resistor one to the inverting input of the op-amp. Check the data sheet for your specific op-amp to determine which pin corresponds to the inverting input. On many op-amps, this is pin two. The pair of capacitor one and resistor one constitutes the high pass section of your filter. The cutoff frequency is the inverse of 2*pi*R1*C1.
- 4
  Connect capacitor two across the inverting input as well as the output of the op-amp.
- 5
  Connect resistor two across the inverting input as well as the output of the op-amp. Again, check the data sheet for your op-amp to determine which pin corresponds to the output. On many op-amps, pin six is the output. The combination of resistor two and capacitor two constitutes the low pass section of the filter. The cutoff frequency is the inverse of 2*pi*R2*C2.
- 6
  Connect the non-inverting input of your op-amp to ground. Check the data sheet to determine which pin corresponds to the non-inverting input. On many op-amps, pin three is the non-inverting input.

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