Calculate Bandpass Active Filters




Active filter design precautions


When building the active filter circuit, high tolerance components must be used to obtain the best performance. Typically they should be 1% or better.

A further item to ensure the optimum operation of the circuit is to ensure that the source impedance is less than about 100 ohms. Additionally the load impedance should be greater than about 2 M Ohms.


  • Q factor
  • The Q Factor is a measure of how "Selective" or "Un-selective" the band pass filter is towards a given spread of frequencies. The lower the value of the Q factor the wider is the bandwidth of the filter and consequently the higher the Q factor the narrower and more "selective" is the filter.


More info about Active Band Pass Filters can be found  here  or   here   or with the help of  Google 


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4 Pole Bandpass Active Filter


4 pole bandpass filter

Input

Calculated Values

Filter Type :
Capacitors : uF
Center Freq : Hz
3dB Bandwidth : Hz
Voltage Gain : Vu
C1,C2,C3,C4 = uF
R1 = Ω
R2 = Ω
R3 = Ω
R4 = Ω
R5 = Ω
R6 = Ω
Amplification = dB

Section 1 2
Q
Freq
Q values up to about 20 are reasonable.
Above that may result in an unstable circuit.

Filter Response for Butterworth, Chebyshev & Bessel



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6 Pole Bandpass Active Filter



6 Pole bandpass filter

Input

Calculated Values

Filter Type :
Capacitors : uF
Center Freq : Hz
3dB Bandwidth : Hz
Voltage Gain : Vu
C1,C2,C3,C4,C5,C6 = uF
R1 = Ω
R2 = Ω
R3 = Ω
R4 =
R5 =
R6 =
R7 =
R8 =
R9 =
Amplification = dB

Section 1 2 3
Q
Freq

Q values up to about 20 are reasonable.
Above that may result in an unstable circuit.

Filter Response for Butterworth, Chebyshev & Bessel



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Narrow 2 Pole Bandpass Active Filter (Bessel)



Input

Computed Values

Capacitors : uF
Center Freq : Hz
3dB Bandwidth : Hz
Voltage Gain : Vu
C1,C2 = uF nF
R1 = Ω
R2 = Ω
R3 = Ω
Amplification = dB
Filter Q =
  • Use a potentiomter for R1 to fine-adjust the gain.
  • Use a potentiomter for R2 to fine-adjust the center frequency.


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