Sallen-Key Filter Calculator

The Sallen-Key Filter Calculator designs or analyzes a second-order active filter circuit — a popular op-amp topology used to selectively pass or block frequencies in audio, signal processing, and electronics applications. Select Low-Pass or High-Pass as your Filter Type, then choose a Calculation Mode: enter your Cutoff Frequency, Q Factor, and DC Gain to get the required R1, R2, C1, and C2 component values — or enter your existing component values to find the resulting cutoff frequency and Q factor.

Hz

0.707 for Butterworth response

kΩ
kΩ
nF
nF
V/V

Results

Cutoff Frequency

--

Q Factor

--

R1 Value

--

R2 Value

--

C1 Value

--

C2 Value

--

More Electrical & Electronics Tools

Frequently Asked Questions

What is a Sallen-Key filter?

A Sallen-Key filter is a popular active filter topology that uses an op-amp as a voltage follower with two resistors and two capacitors to create second-order filtering. It's also known as a VCVS (Voltage Controlled Voltage Source) filter.

What is the Q factor and how does it affect filter response?

The Q factor determines the sharpness of the filter response at the cutoff frequency. A Q of 0.707 gives a maximally flat Butterworth response, while higher Q values create more peaking near the cutoff frequency.

How do I choose component values for my Sallen-Key filter?

Start by specifying your desired cutoff frequency and Q factor. The calculator will determine appropriate R and C values. For best performance, keep resistor values between 1kΩ and 100kΩ and use standard capacitor values.

What's the difference between low-pass and high-pass Sallen-Key filters?

Low-pass filters allow frequencies below the cutoff to pass while attenuating higher frequencies. High-pass filters do the opposite, passing frequencies above the cutoff. The component arrangement differs between the two types.

Can I use different values for R1/R2 and C1/C2?

Yes, you can use different values for the resistors and capacitors. Equal values (R1=R2, C1=C2) simplify the design, but unequal values allow more flexibility in achieving specific Q factors and using standard component values.

What op-amp should I use for a Sallen-Key filter?

Choose an op-amp with sufficient bandwidth (at least 10x your cutoff frequency), low input bias current, and appropriate slew rate. Popular choices include TL072, LM358, or OPA2134 depending on your audio quality requirements.

How accurate is the calculated cutoff frequency in practice?

The accuracy depends on component tolerances and op-amp characteristics. Use 1% resistors and 5% capacitors for better accuracy. The actual cutoff may vary by ±10% due to component tolerances.

What are the advantages of Sallen-Key topology over other active filters?

Sallen-Key filters offer unity gain without additional components, low sensitivity to op-amp parameters, simple design with few components, and good high-frequency performance. They're ideal for audio applications.