What does a Bessel filter do?
The Bessel filter (sometimes called the “Thomson” filter) is optimized to provide a constant group delay in the filter passband, while sacrificing sharpness in the magnitude response. Bessel filters are sometimes used in applications where a constant group delay is critical, such as in analog video signal processing.
What does a notch filter do?
Notch filters are used to remove a single frequency or a narrow band of frequencies. In audio systems, a notch filter can be used to remove interfering frequencies such as powerline hum. Notch filters can also be used to remove a specific interfering frequency in radio receivers and software-defined radio.
How is the Bessel filter characterized by its transfer function?
The Bessel filter maximizes the flatness of the group delay curve at zero frequency. A Bessel low-pass filter is characterized by its transfer function: is a frequency chosen to give the desired cut-off frequency. The filter has a low-frequency group delay of .
Where are the pole locations for a Bessel filter?
The pole locations for the Bessel filter with a cutoff frequency 1 rad/s are outside the unit circle. Pole locations for an N = 4 Bessel filter are shown in Figure 14.19. FIGURE 14.19.
Is there an overshoot in the Bessel filter?
There is little or no overshoot in the step response (Figure 14.21 ). The group delay exhibits a very flat response in the passband ( Figure 14.22 ). FIGURE 14.20. Bessel filter magnitude response, order N = 2–8, shown for filters with −3-dB cutoff frequency of 1 rad/s.
Is the group delay constant in the Bessel filter?
Note that the transition from the pass band to the stop band is much slower than for other filters, but the group delay is practically constant in the passband. The Bessel filter maximizes the flatness of the group delay curve at zero frequency.