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.243:
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
The Sigma Delta ADC anti
-
alias filter
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 2.5 Hz to 125 kHz
0.1 dB passband ripple (ωp)
DC to 0.8 * ωc. Limited to 7 kHz for
±
1 mV range
Stopband attenuation (δs)
-
180 dB (
-
160 dB for
±
1 mV range)
Roll
-
off
-
72 dB/octave
Frequency [kHz]
Frequency [kHz]
Magnitude
[dB
]
Magnitude
[dB
]
100
Magnitude [%]
102.33
101.74
101.16
100.58
99.43
98.86
98.29
97.72
1000
100
10
1
0.1
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
Magnitude
[dB
]
±
1 mV Butterworth 125 kHz Overview
±
1 mV Butterworth 125 kHz Passband flatness
100
Magnitude [%]
102.33
101.74
101.16
100.58
99.43
98.86
98.29
97.72
1000
100
10
1
0.1
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
Magnitude
[dB
]
-160
-140
-120
-100
-80
-60
-40
-20
0
0.1
1
10
100
1000
±
10 V Butterworth 125 kHz Overview
±
10 V Butterworth 125 kHz Passband flatness
-160
-140
-120
-100
-80
-60
-40
-20
0
0.1
1
10
100
1000
Figure A.244:
Representative Butterworth IIR examples
(1)
Measured using Fluke 5730A calibrator, DC normalized
GEN3i
I3763-3.1 en HBM: public
657
