🔌 Chebyshev Filter Calculator

1. Select the filter topology (Tee or Pi) using the dropdown.
2. Select the passband ripple (0.5 dB or 3 dB).
3. Enter the cutoff frequency (fc) in Hz, kHz or MHz.
4. Enter the source/load impedance (R) in ohms.
5. Click Calculate to get the three component values for the chosen ripple and topology.

What is the difference between Chebyshev and Butterworth filters?

The main difference is the passband response. A Butterworth filter is maximally flat \u2014 zero ripple in the passband \u2014 but has a gentler roll-off (60 dB/decade for 3rd order). A Chebyshev filter accepts equal-amplitude ripple in the passband (typically 0.5 dB or 3 dB) in exchange for a steeper roll-off (approximately 65\u201370 dB/decade for 3rd order). If your application needs sharp frequency selectivity and can tolerate some passband gain variation, choose Chebyshev. If signal fidelity in the passband is paramount, choose Butterworth.

What does 0.5 dB ripple vs 3 dB ripple mean in practice?

The ripple value specifies the maximum gain variation within the passband. A 0.5 dB ripple means the gain swings by \u00B10.5 dB (a total of 1 dB peak-to-peak) \u2014 about \u00B15.9% amplitude error. A 3 dB ripple means \u00B13 dB (\u00B141% amplitude error), which is far more noticeable. The 3 dB option gives steeper roll-off, but the larger amplitude variation may be unacceptable for precision measurement or communication systems. For most audio and RF applications, 0.5 dB is the preferred compromise.

Why are the Chebyshev g-values different from Butterworth g-values?

The g-values (normalised prototype element values) are derived from different mathematical polynomials. Butterworth uses Butterworth polynomials (all poles on a circle in the complex plane), producing a maximally flat response with g1 = 1.0, g2 = 2.0, g3 = 1.0 for n = 3. Chebyshev uses Chebyshev polynomials of the first kind, which place poles on an ellipse, producing equi-ripple passband behaviour with different g-values: for 3 dB ripple, g1 = 3.3487, g2 = 0.7117, g3 = 3.3487. The elliptical pole placement is what gives the steeper roll-off.

Can I use this Chebyshev filter calculator for RF preselector design?

Yes. The 3 dB-ripple Chebyshev is a popular choice for RF preselector front-end filters because of its steep roll-off, which helps reject strong out-of-band signals and image frequencies. For a 50 \u03A9 system at 14 MHz (HF amateur radio), enter fc = 14 MHz, R = 50 \u03A9, and select 3 dB ripple with Tee LP topology. Be aware that real RF inductors should have a high Q factor (ideally > 100) to preserve the designed ripple shape; low-Q inductors will round off the ripple and reduce selectivity.

Does the Chebyshev filter have worse group delay than Butterworth?

Yes. The Chebyshev filter\u2019s steeper magnitude roll-off comes at the cost of more non-linear phase response near the cutoff frequency, which means group delay peaks and varies more than in a Butterworth filter of the same order. For narrowband signals this is rarely a problem, but for wideband digital modulations (e.g. QAM, OFDM), the group-delay variation can cause inter-symbol interference. If linear phase is critical, consider a Bessel (Thomson) filter or a linear-phase equaliser stage.

How do I choose between Tee and Pi topology for a Chebyshev filter?

Both topologies produce the same Chebyshev response. The choice typically comes down to practical factors: at some impedance-frequency combinations, the Tee network may yield more convenient standard inductor values, while at others the Pi network is preferable. In RF stripline or microstrip layouts, the Pi network is sometimes easier to implement because shunt capacitors can be realised as stubs. In general, try both and select whichever gives component values closest to standard E12/E24 series values.

Is this calculator suitable for active filter design with op-amps?

No. This calculator is designed for passive LC ladder networks (inductors and capacitors only). For active RC filter designs using operational amplifiers, use our Sallen-Key filter calculator instead. Active filters avoid bulky inductors and are preferred for audio and low-frequency applications, while passive LC filters are standard for RF and high-frequency work where op-amp bandwidth is insufficient.

When using this calculator, remember that the Chebyshev design assumes ideal, lossless components \u2014 real-world inductors and capacitors have parasitic resistance and self-capacitance/inductance that will reduce the actual ripple and roll-off performance. At RF frequencies above 100 MHz, use high-Q surface-mount components and minimise trace parasitics. The 3 dB ripple option provides the steepest roll-off but introduces noticeable gain variation in the passband; for signal chains where amplitude accuracy matters (e.g. measurement instruments), prefer 0.5 dB ripple or switch to a Butterworth design. Also, be aware that the Chebyshev filter\u2019s group delay is more non-linear near the cutoff frequency than a Butterworth\u2019s, which can cause signal distortion in wideband digital communications. If you need both sharp selectivity and flat passband, consider an elliptic (Cauer) filter or a cascade approach. For audio applications, large inductor values may be impractical \u2014 use active filter topologies like Sallen-Key instead. Always verify your design with a network analyser or SPICE simulation before committing to hardware.