Bessel IIR Filter (Digital Anti
-
Alias)
δs
ωp
ωs
Passband
Stopband
δp : Passband ripple
δs: Stopband attenuation
ωp
ωc
ωs
: Passband frequency
: Corner frequency
: Stopband frequency
Frequency [kHz]
Magnitude [dB]
ωc
1 + δp
1 - δp
-3 dB
Figure A.263:
Digital Bessel IIR Filter
When Bessel IIR filter is selected, this is always a combination of the built
-
in anti
-
alias filter of the Sigma Delta ADC and a digital Bessel 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
Bessel IIR Filter
Characteristic
12
-
pole Bessel style IIR
8
-
pole Bessel style IIR filter frequencies ωc = 25 kHz and ωc = 12.5 kHz
User selection
Auto tracking to sample rate divided by: 10, 20, 40, 100
User selects divide factor from current sample rate, software then adjusts filter when sample
rate is changed
Bandwidth (ωc)
User selectable from 40 Hz to 25 kHz
0.1 dB passband flatness (ωp)
(1)
DC to ωc/10
Stopband attenuation (δs)
80 dB
Roll
-
off
72 dB/octave for 12
-
pole filters; 48 dB/octave for 8
-
pole filters
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
1000
100
10
1
0.1
1000
100
10
1
0.1
±1 V Bessel IIR 25 kHz Overview
±10 V Bessel 25 kHz Overview
±10 V Bessel 25 kHz Passband flatness
±1 V Bessel IIR 25 kHz Passband flatness
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Frequency [kHz]
Magn
itud
e [dB
]
-150
-130
-110
-90
-70
-50
-30
-10
10
Frequency [kHz]
Magn
itud
e [dB
]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
100
10
1
0.1
0
Magn
itud
e [%
]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Figure A.264:
Representative Bessel IIR examples
(1)
Measured using Fluke 5700A calibrator, DC normalized
GEN3i
I3763-3.1 en HBM: public
685
