RLC Filter Designer
Adjust the Resistor (R), Inductor (L), and Capacitor (C) values using the sliders below. The calculator will instantly update the filter's characteristics and visualize its frequency response on the chart.
Calculated Characteristics
Core Concepts Explained
To truly master bandpass filters, it's essential to understand the key parameters that define their behavior. This section breaks down the fundamental concepts, explaining what each one means and how it impacts the filter's performance.
What is a Bandpass Filter?
A bandpass filter is an electronic circuit that allows signals with a frequency within a specific range to pass through, while blocking or attenuating signals with frequencies outside that range. It's like a gatekeeper for frequencies.
Center Frequency (fc)
This is the midpoint of the frequency range that the filter passes. It's the frequency at which the filter has its maximum signal gain. In our interactive chart, this is the peak of the curve.
Bandwidth (BW)
Bandwidth defines the width of the "passband". It is the difference between the upper and lower cutoff frequencies (fH - fL), which are the points where the signal power is reduced by half (-3dB).
Quality Factor (Q)
The Q factor is a measure of the filter's selectivity or "sharpness". A high Q factor means a narrow bandwidth (very selective), while a low Q factor results in a wide bandwidth (less selective).
Cutoff Frequencies (-3dB)
These are the boundaries of the passband. The Lower Cutoff (fL) and Upper Cutoff (fH) are the frequencies where the output signal's amplitude is 70.7% (or -3dB) of the signal at the center frequency.
Impedance (Z)
Characteristic impedance is a key parameter in filter design, representing the ratio of voltage to current. For an RLC circuit, it's calculated as √(L/C) and determines how the filter interacts with source and load impedances.
Key Formulas
For engineers, students, and hobbyists, understanding the math behind the magic is crucial. Here are the fundamental formulas used to calculate the characteristics of a series RLC bandpass filter. These equations are the engine running the interactive calculator.
| Parameter | Formula | Description |
|---|---|---|
| fc | 1 / (2π * √(L * C)) | Resonant or Center Frequency |
| BW | R / (2π * L) | Bandwidth in Hz |
| Q | (1 / R) * √(L / C) | Quality Factor (Dimensionless) |
| Z | √(L / C) | Characteristic Impedance in Ohms |
