Second Order High Pass Filter Calculator

Second Order High Pass Filter Equation:

\[ f_c = \frac{1}{2 \pi \sqrt{R1 R2 C1 C2}} \]

Resistor R1:

Resistor R2:

Capacitor C1:

Capacitor C2:

Cutoff Frequency (f_c):

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1. What is a Second Order High Pass Filter?

A second order high pass filter is an electronic circuit that attenuates signals with frequencies lower than the cutoff frequency while allowing higher frequencies to pass. It has a steeper roll-off (40 dB/decade) compared to first order filters (20 dB/decade).

2. How Does the Calculator Work?

The calculator uses the second order high pass filter equation:

\[ f_c = \frac{1}{2 \pi \sqrt{R1 R2 C1 C2}} \]

Where:

\( f_c \) — Cutoff frequency (Hz)
\( R1 \) — First resistor value (Ω)
\( R2 \) — Second resistor value (Ω)
\( C1 \) — First capacitor value (F)
\( C2 \) — Second capacitor value (F)
\( \pi \) — Pi constant (~3.1416)

Explanation: The cutoff frequency is determined by the product of the resistors and capacitors in the filter circuit.

3. Importance of Cutoff Frequency

Details: The cutoff frequency is the point where the output signal is attenuated by 3 dB (-3 dB point). It's a crucial parameter in filter design that determines which frequencies are passed and which are blocked.

4. Using the Calculator

Tips: Enter resistor values in ohms (Ω) and capacitor values in farads (F). For practical values, capacitors are often in microfarads (μF) or nanofarads (nF). All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between first and second order filters?
A: Second order filters have steeper roll-off (40 dB/decade vs 20 dB/decade) and better attenuation of stopband frequencies.

Q2: What are typical applications of high pass filters?
A: Used in audio systems, communication circuits, and signal processing to remove DC offset or low-frequency noise.

Q3: Can I make R1=R2 and C1=C2?
A: Yes, using equal components simplifies the equation to \( f_c = \frac{1}{2 \pi R C} \).

Q4: How does component tolerance affect the cutoff frequency?
A: Component tolerances directly affect accuracy. 5% tolerance components can lead to ~10% variation in actual cutoff frequency.

Q5: What about Sallen-Key topology?
A: This calculator works for basic second order filters. Sallen-Key filters have additional considerations like gain and Q factor.