What types of analog filters are there?

The major analog filters are Butterworth (maximally flat magnitude), Chebyshev Type I (equiripple in the passband), Chebyshev Type II (equiripple in the stopband), Elliptic/Cauer (equiripple in both bands with the steepest roll-off), and Bessel (maximally flat group delay).

How should I choose an analog filter?

Choose Butterworth or Chebyshev Type II for passband flatness, Chebyshev Type I or Elliptic for a sharp cutoff, Elliptic to meet specifications with the minimum order, and Bessel when group delay (linear phase) is important.

Analog Filters

Analog filters process continuous-time signals. IIR (infinite impulse response) digital filters are often obtained by digitizing analog filter designs using techniques such as the bilinear transform.

Classical Analog Filters

Filter	Passband	Stopband	Characteristics
Butterworth	monotonic	monotonic	maximally flat
Chebyshev Type I	equiripple	monotonic	sharp cutoff
Chebyshev Type II	monotonic	equiripple	no passband ripple
Elliptic (Cauer)	equiripple	equiripple	steepest roll-off
Bessel	monotonic	monotonic	maximally flat group delay

Butterworth Filter

An analog filter with maximally flat magnitude response in the passband. Its phase characteristics are better than Chebyshev or Elliptic filters, though not as good as Bessel.

Chebyshev Filters

Analog filters with equiripple characteristics in either the passband or the stopband. Available in Type I and Type II, achieving a steeper transition than Butterworth.

Elliptic Filter (Cauer Filter)

Features equiripple behavior in both the passband and the stopband, achieving the steepest transition for a given filter order.

Bessel Filter

An analog filter with maximally flat group delay. Suitable for applications where linear phase is important.

Selection Guidelines

Passband flatness is important → Butterworth or Chebyshev Type II
Narrow transition bandwidth needed → Chebyshev Type I or Elliptic
Meet specifications with minimum order → Elliptic filter
Group delay (linear phase) is important → Bessel
Passband ripple acceptable, sharp cutoff needed → Chebyshev Type I