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.96:
Representative Bessel IIR examples
When Bessel IIR filter is selected, this is always a combination of an analog Bessel anti
-
alias filter and a digital Bessel IIR filter.
Analog anti
-
alias filter bandwidth
400 kHz
±
25 kHz (
-
3 dB)
Analog anti
-
alias filter characteristic
7
-
pole Bessel, optimal step response
Bessel IIR filter characteristic
8
-
pole Bessel style IIR
Bessel IIR filter user selection
Auto tracking for sample rate divided by: 10, 20, 40, 100
The user selects a division factor from the current sample rate; software then adjusts the
filter when the sample rate is changed.
Bessel IIR filter bandwidth (ωc)
User selectable from 0.4 Hz to 200 kHz
Bessel IIR 0.1 dB passband (ωp)
(1)
DC to 0.14 * ωc
Bessel IIR filter stopband attenuation (δs)
60 dB
With the Bessel IIR filter bandwidth selection of ωc = 200 kHz, a peak of
-
55 dB occurs
between 1.6 MHz and 1.8 MHz due to limited analog anti
-
alias filter amplitude reduction.
At lower bandwidth selections, the digital filter reduces this peak to
-
60 dB.
Bessel IIR filter roll
-
off
48 dB/octave
Frequency [kHz]
1000
100
10
1
0.1
20 V:
Bessel 200 kHz Passband flatness
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
20 V: Bessel 200 kHz Overview
4 V: Bessel 200 kHz Overview
-130
-110
-90
-70
-50
-30
-10
10
0.1
1
10
100
1000
10000
Frequency [kHz]
1000
100
10
1
0.1
4 V:
Bessel 200 kHz Passband flatness
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
-130
-110
-90
-70
-50
-30
-10
10
0.1
1
10
100
1000
10000
0
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
0
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Magnitude [dB]
Magnitude [dB]
Magnitude [
%
]
Magnitude [dB]
Magnitude [dB]
Magnitude [
%
]
Figure A.97:
Representative Bessel IIR examples
(1)
Measured using a Fluke 5700A calibrator, DC normalized
GEN3i
I3763-3.1 en HBM: public
503
