Main Frame (acces to all the site)

How to choose a filter ?

Filter property

Butterworth
Chebyshev
Inverse Chebyshev
Bessel - also called Thomson

Advantages:

Maximally flat magnitude response in the pass-band.
Good all-around performance.
Pulse response better than Chebyshev.
Rate of attenuation better than Bessel.

Diavantages:

Some overshoot and ringing in step response.

Advantages:

Better rate of attenuation beyond the pass-band than Butterworth.

Ripple in pass-band.
Considerably more ringing in step response than Butterworth.

This filter response has the steeper initial rate of attenuation beyond the cutoff frequency than Butterworth.This advantage comes at the penalty of amplitude variation(ripple) in the pass-band. Unlike Butterworth and Bessel response, which have 3dB attenuation at the cutoff frequency,Cebyshev cutoff frequency is defined as the frequency at which the response falls below the ripple band. For even-order filters, all riple is above the dc-normalized passband gain response, so cutoff is at 0dB. For odd-order filters, all riple is below the dc-normalized passband gain response, so cutoff is at -(ripple) dB. For a given number of poles, a steeper cutoff can be achieved by allowing more pass-band ripple. The Chebyshev has more ringing in its pulse response than the Butterworth - especially for high-ripple designs. Back

Advantages:

Flat magnitude response in pass-band with steep rate of attenuation in transition-band.

Diavantages:

Ripple in stop-band.
Some overshoot and ringing in step response.

As its name implies, this filter type is cousin to the Chebyshev. The difference is that the ripple of the Inverse Chebyshev filter is confined to the stop-band. This filter type has a steep rate of roll-of and a flat magnitude response in pass-band. Cutoff of the Inverse Chebyshev is defined as the frequency where the response first enters the specified stop-band. Step response of the Inverse Chebyshev is similar to the Butterworth. Back

Advantages:

Best step response-very little overshoot or ringing.

Diavantages:

Slower initial rate of attenuation beyond the pass-band than Butterworth.

Due to its linear phase response, this filter has excellent pulse response (minimal overshoot and ringing). For a given number of poles, its magnitude response is not as flat, nor is its initial rate of attenation beyond the -3dB cutoff frequency as steep as the Butterworth.It takes a higher-order Bessel filter to give a magnitude response similar to a given Butterworth filter, but the pulse response fidelity of the Bessel filter may make the added complexity worthwile. Back