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Butterworth IIR Filter (Digital Anti
-
Alias)
Passband Stopband
Magnitude [dB]
δp: Passband ripple
δs: Stopband attenuation
ωp:
ωc:
Passband frequency
Corner frequency
Stopband frequency ωs:
ωp ωs
Frequency [kHz]
ωc
1 + δp
1 - δp
-3 dB
δs
Figure A.265: Digital Butterworth IIR Filter
When Butterworth IIR filter is selected, this is always a combination of the built
-
in anti
-
alias filter of the Sigma Delta ADC and a digital Butterworth
IIR filter.
Analog anti
-
alias filter
Characteristic Sigma delta, optimal frequency response
-
3 dB low pass bandwidth 100 kHz
±
5 kHz for sample rates 250 kS/s and 125 kS/s
80 kHz
±
5 kHz for all other sample rates
Butterworth IIR Filter
Characteristic
12
-
pole Butterworth style IIR
User selection Auto tracking to sample rate divided by: 4, 10, 20, 40
User selects divide factor from current sample rate, software then adjusts filter when sample
rate is changed.
Bandwidth (ωc) User selectable from 100 Hz to 62.5 kHz
0.1 dB passband flatness (ωp)
(1) DC to ωc/2 or maximum 10 kHz
Stopband attenuation (δs) 80 dB
Filter roll
-
off
72 dB/octave
Frequency [kHz]
1000 100 10 1 0.1
Frequency [kHz]
Magnitude [dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
±1 V Butterworth IIR 62.5 kHz Overview ±1 V Butterworth IIR 62.5 kHz Passband flatness
±10 V Butterworth IIR 62.5 kHz Overview ±10 V Butterworth IIR 62.5 kHz Passband flatness
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Frequency [kHz]
1000 100 10 1 0.1
Frequency [kHz]
Magnitude [dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
1000 100 10 1 0.1
1000 100 10 1 0.1
Figure A.266: Representative Butterworth IIR examples
(1) Measured using Fluke 5700A calibrator, DC normalized
GEN3i
686 I3763-3.1 en HBM: public