4 order filter circuit schematic

TL081 4 Order Filter Circuit

Filters with high orders are designed usually with 2 or more cascaded sections. This order 4 filter need only one OA IC , so we can achieve lower distorsions, lower intermodulation …
Resistors values represent the load on the OA output, the maximum TL081 load is 2kΩ . R1-R4 build a 2.5kΩ impedance and so the external load cannot be lower than 10kΩ .

The filter characteristic is a Bessel polinome. With the actual components value, at -3dB the frequency is 1kHz. You can obtain different frequencies by changing the components value.

4-th order filter circuit schematic

4 order filter circuit schematic

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  • Andrew

    Thank you for sharing this. I had not run across practical looking circuits for 4th order filters with a single op amp other than RC stages followed by a 2nd order. An available reference paper suggests that this unity gain / unity feedback version of the circuit will be sensitive to variations in op amp gain. I would like to check this out before just trusting the reference, though; it is a nice looking circuit and the performance may be fine as long as the op amp gain stays high enough.

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