In the PSV 300-F and -U low pass filters with 3rd order Bessel characteristicsIn the PSV 300-F and -U low pass filters with 3rd order Bessel characteristics
and cutoff frequenciand cutoff frequencies of 5es of 5 kHz, 20kHz, 20kHz or 100kHz or 100kHz are used. CharacterikHz are used. Characteristic forstic for
Bessel filters is the phase linearity from the Bessel filters is the phase linearity from the frequency zero up to frequency zero up to the cutoffthe cutoff
frequency, i.e. the phase shift increases in proportion to the frequency. Thefrequency, i.e. the phase shift increases in proportion to the frequency. The
filter howeverfilter however, causes amplitude errors in the , causes amplitude errors in the pass band which can be pass band which can be roughlyroughly
estimated:estimated:
Up to 20% of the cutoff frequency, the maximum amplitude error isUp to 20% of the cutoff frequency, the maximum amplitude error is
±±
1%.1%.
At the cutoff frequency, the amplitude error isAt the cutoff frequency, the amplitude error is
−−
3dB (approx.3dB (approx.
−−
30%).30%).
The phase shift increases in proportion to The phase shift increases in proportion to the frequency from Zero degree athe frequency from Zero degree att
the frequency Zero the frequency Zero to approximatelyto approximately
−−
100 degrees at the cutoff frequency100 degrees at the cutoff frequency
(refer to(refer tofi
figugurere 4.4.66). Due to ). Due to this linear phase frequency response, the filterthis linear phase frequency response, the filter
shows optimal transmissioshows optimal transmission behavior for pulses, an behavior for pulses, as all frequencies of as all frequencies of a
complex wave are subjected to the same time delay. Thus the shape of thecomplex wave are subjected to the same time delay. Thus the shape of the
pulse is not falsified but it is merely delayed.pulse is not falsified but it is merely delayed.
The complete amplitude frequency response of a 3The complete amplitude frequency response of a 3rd order Bessel low passrd order Bessel low pass
filter is shown infilter is shown infifigugurere 4.4.44. The frequency is normalized to the cutoff. The frequency is normalized to the cutoff
frequency ffrequency f
cc
..
Figure 4.4: Amplitude frequency response of a 3rd order Bessel low pass filterFigure 4.4: Amplitude frequency response of a 3rd order Bessel low pass filter
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