# 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.

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## 4 Pole Bandpass Active Filter ## Calculated Values

 Filter Type : Butterworth Chebyshev 0.1 dB Bessel 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 ## Calculated Values

 Filter Type : Butterworth Chebyshev 0.1 dB Bessel 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) ## Computed Values

 Capacitors : uF Center Freq : Hz 3dB Bandwidth : Hz Voltage Gain : Vu
 C1,C2 = uF nF R1 = kΩ Ω R2 = kΩ Ω R3 = kΩ 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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