RLC Bandpass Filter Calculator

Calculator Inputs

Example Data Table

Formula Used

The resonant frequency is calculated from the inductor and capacitor values.

f0 = 1 / (2π√LC)

The series circuit quality factor uses resistance in the current path.

Qseries = ω0L / R

The parallel circuit quality factor uses the shunt resistance value.

Qparallel = R / ω0L

Bandwidth is linked to center frequency and quality factor.

BW = f0 / Q

For a series filter, the direct bandwidth form is:

BWseries = R / 2πL

For a parallel filter, the direct bandwidth form is:

BWparallel = 1 / 2πRC

The calculator also estimates cutoff frequencies, test-frequency gain, phase angle, tolerance range, and required resistance for target bandwidth or target Q.

How to Use This Calculator

1. Select series or parallel RLC configuration.
2. Enter resistance, inductance, and capacitance values.
3. Choose the correct unit beside each input.
4. Add a test frequency for gain and phase checking.
5. Enter source voltage to estimate output voltage.
6. Add target bandwidth or target Q when designing backward.
7. Set inductor and capacitor tolerances for frequency spread.
8. Press Calculate Filter to show results below the header.
9. Use CSV or PDF buttons to download the same result.

RLC Bandpass Filter Guide

What the Filter Does

An RLC bandpass filter passes a chosen range of frequencies. It reduces signals below and above that range. The center of the passband is called resonance. At resonance, inductive reactance and capacitive reactance are equal. Their effects cancel in a useful way. This creates a strong response at one main frequency.

Series and Parallel Behavior

A series RLC bandpass filter often takes output across the resistor. Current is highest near resonance. A lower series resistance gives a higher quality factor. That means a narrower passband. A parallel RLC circuit behaves differently. Its impedance is highest near resonance. Higher parallel resistance usually raises selectivity.

Why Quality Factor Matters

Quality factor shows how sharp the filter is. A low Q gives a broad response. This is useful when a wide range must pass. A high Q gives a narrow response. This is useful for tuning, rejection, and channel selection. Bandwidth equals center frequency divided by Q. So Q and bandwidth move in opposite directions.

Using Real Components

Real inductors and capacitors are not perfect. Their values can vary with tolerance, temperature, and frequency. Coils also have winding resistance. Capacitors may have loss. These effects can shift the center frequency. This calculator includes tolerance estimates. They help you see the possible frequency range before building the circuit.

Design Tips

Start with the required center frequency. Choose practical capacitor and inductor values. Then set resistance to reach the needed bandwidth. Test the design at the expected signal frequency. Review gain, phase, and detuning. Export the result when you need a record for reports, class work, or prototype notes.