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 L.67:
Digital Bessel IIR Filter
When Bessel IIR filter is selected, this is always a combination of the anti
-
alias filter built
-
in the Sigma Delta ADC and a digital Bessel IIR filter.
Analog anti
-
alias filter
Characteristic
Sigma delta, optimal frequency response
Low pass
-
3 dB bandwidth
80 kHz
±
5 kHz
Bessel IIR Filter
Characteristic
12
-
pole Bessel style IIR
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 2 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
Frequency [kHz]
Frequency [kHz]
Magnitude [dB]
-130
-110
-90
-70
-50
-30
-10
10
-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 2 kHz Overview
±10 V Bessel 2 kHz Overview
±10 V Bessel 2 kHz Passband flatness
±1 V Bessel IIR 2 kHz Passband flatness
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Frequency [kHz]
Magnitude [dB]
Frequency [kHz]
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
10
1
0.1
0.01
10
1
0.1
0.01
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Figure L.68:
Representative Bessel IIR examples
(1)
Measured using Fluke 5700A calibrator, DC normalized
GEN3i
I3763-3.1 en HBM: public
1127
