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LS204C 数据表(PDF) 6 Page - STMicroelectronics |
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LS204C 数据表(HTML) 6 Page - STMicroelectronics |
6 / 10 page APPLICATION INFORMATION : Active low-pass filter BUTTERWORTH The Butterworth is a ”maximally flat” amplitude response filter (figure 10) Butterworth filters are used for filtering signals in data acquisition systems to prevent aliasing errors in samples-data applica- tions and for general purpose low-pass filtering. The cut-off frequency Fc, is the frequency at which the amplitude response is down 3dB. The attenu- ation rate beyond the cutoff frequency is n6 dB per octave of frequency where n is the order (number of poles) of the filter. Other characteristics : . Flattest possible amplitude response . Excellent gain accuracy at low frequency end of passband BESSEL The Bessel is a type of ”linear phase” filter. Be- cause of their linear phase characteristics, these filters approximate a constant time delay over a limited frequency range. Bessel filters pass tran- sient waveforms with a minimum of distortion. They are also used to provide time delays for low pass filtering of modulated waveforms and as a ”running average” type filter. The maximum phase shift is −n Π 2 radians where n is the order (number of poles) of the filter. The cut-off frequency fc, is defined as the frequency at which the phase shift is one half of this value. For accurate delay, the cut-off frequency should be twice the maximum signal frequency. The following table can be used to obtain the -3dB frequency of the filter. 2 Pole 4 Pole 6 Pole 8 Pole -3dB Frequency 0.77fc 0.67fc 0.57fc 0.50fc Other characteristics : . Selectivity not as great as Chebyschev or But- terworth . Very little overshoot response to step inputs . Fast rise time CHEBYSCHEV Chebyschev filters have greater selectivity than either Bessel ro Butterworth at the expense of ripple in the passband (figure 11). Chebyschev filters are normally designed with peak-to-peak ripple values from 0.2dB to 2dB. Increased ripple in the passband allows increased attenuation above the cut-off frequency. The cut-off frequency is defined as the frequency at which the amplitude response passes through the specificed maximum ripple band and enters the stop band. Other characteristics : . Greater selectivity . Very non-linear phase response . High overshoot response to step inputs The table below shows the typical overshoot and settling time response of the low pass filters to a step input. Number of Poles Peak Overshoot Settling Time (% of final value) % Overshoot ±1% ±0.1% ±0.01% Butterworth 2 4 6 8 4 11 14 16 1.1Fcsec. 1.7/fc 2.4/fc 3.1/fc 1.7Fcsec. 2.8/fc 3.9/fc 5.1/fc 1.9Fcsec. 3.8/fc 5.0/fc 7.1/fc Bessel 2 4 6 8 0.4 0.8 0.6 0.1 0.8/fc 1.0/fc 1.3/fc 1.6/fc 1.4/fc 1.8/fc 2.1/fc 2.3/fc 1.7/fc 2.4/fc 2.7/fc 3.2/fc Chebyschev (ripple ±0.25dB) 2 4 6 8 11 18 21 23 1.1/fc 3.0/fc 5.9/fc 8.4/fc 1.6/fc 5.4/fc 10.4/fc 16.4/fc - - - - Chebyschev (ripple ±1dB) 2 4 6 8 21 28 32 34 1.6/fc 4.8/fc 8.2/fc 11.6/fc 2.7/fc 8.4/fc 16.3/fc 24.8/fc - - - - Design of 2nd order active low pass filter (Sallen and Key configuration unity gain-op-amp) LS204 6/10 |
类似零件编号 - LS204C |
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类似说明 - LS204C |
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