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 L.69:
Digital Butterworth IIR Filter
When Butterworth IIR filter is selected, this is always a combination of the anti
-
alias filter built
-
in the Sigma Delta ADC and a digital Butterworth
IIR filter.
Analog anti
-
alias filter
Characteristic
Sigma delta, optimal frequency response
Low pass bandwidth
80 kHz
±
5 kHz (
-
3 dB)
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 5 kHz
0.1 dB passband flatness (ωp)
(1)
DC to ωc/2
Stopband attenuation (δs)
80 dB
Filter roll
-
off
72 dB/octave
Frequency [kHz]
Frequency [kHz]
Magnitude [dB]
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
±1 V Butterworth IIR 5 kHz Overview
±1 V Butterworth IIR 5 kHz Passband flatness
±10 V Butterworth IIR 5 kHz Overview
±10 V Butterworth IIR 5 kHz Passband flatness
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Frequency [kHz]
Frequency [kHz]
Magnitude [dB]
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
-130
-110
-90
-70
-50
-30
-10
10
-130
-110
-90
-70
-50
-30
-10
10
10
1
0.1
0.01
10
1
0.1
0.01
Figure L.70:
Representative Butterworth IIR examples
(1)
Measured using Fluke 5700A calibrator, DC normalized
GEN3t
I3995-3.1 en HBM: public
1091