LC High Pass Filter Calculator

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Calculate an ideal second-order Butterworth LC high-pass filter from cutoff frequency and system impedance, including series capacitor, shunt inductor, and response notes.

Input Parameters

Cutoff Frequency

MHz

-3 dB cutoff frequency for the ideal 2nd-order Butterworth high-pass.

System Impedance

Source/load impedance for prototype scaling.

Results

Series Capacitor

Shunt Inductor

LC Resonant Check

Design Impedance

Ideal Roll-off

Design Note

Equations Used

2nd-Order Butterworth High-Pass: g1 = g2 = 1.4142

Series Capacitor: C = 1 / (g1 × R × 2πfc)

Shunt Inductor: L = R / (g2 × 2πfc)

Ideal Low-Frequency Attenuation: 40 dB/decade below cutoff.

Frequently Asked Questions (FAQ)

Q1: What does this LC high pass filter calculator do?
It calculates an ideal second-order Butterworth high-pass LC section from cutoff frequency and impedance.

Q2: Where are high-pass LC filters used?
They are used for AC coupling, RF front ends, blocking low-frequency signals, and band-shaping networks.

Q3: Why does impedance matter?
The component values are scaled to the source/load impedance. Changing impedance changes L and C values.

Q4: Can I use this for audio filters?
Yes for ideal estimates, but driver/load impedance and component tolerances must be considered.

Q5: Are real inductors ideal?
No. Inductor resistance, core loss, Q, and self-resonance can strongly affect high-frequency behavior.

Disclaimer: This calculator provides ideal high-pass LC filter starting values. Real performance depends on source/load impedance, component Q, parasitics, tolerance, PCB layout, and measurement verification.

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