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.12:
Digital Bessel IIR Filter
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
-
aliasing filter bandwidth
220 kHz
±
20 kHz (
-
3 dB)
Analog anti
-
aliasing filter characteristic
7
-
pole Bessel, optimal step response
Bessel IIR filter characteristic
6
-
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)
Auto tracking the sample rate with the selected Bessel IIR filter; user selection from
0.0125 Hz to 100 kHz
Bessel IIR passband flatness (ωp)
(1)
0.1 dB; DC to 20 kHz @ ωc = 100 kHz
Bessel IIR filter stop band attenuation (δs)
60 dB
With the Bessel IIR filter bandwidth selection of ωc = 100 kHz, a peak of
-
55 dB occurs
between 500 kHz and 1 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
36 dB/Octave
Bessel IIR 100 kHz Overview
10
0
-10
-20
-30
-40
-50
-60
-70
-80
Frequency [kHz]
Ma
gni
tu
de
[dB
]
10000
1000
100
10
1
0.1
1000
100
10
1
0.1
Passband flatness
Frequency [kHz]
Ma
gni
tu
de
[dB
]
0.2
0.1
0.05
0.15
-0.1
-0.15
-0.05
-0.2
0
Figure L.13:
Representative Bessel IIR examples
(1)
Measured using Fluke 5700 calibrator, DC normalized
GEN3i
1040
I3763-3.1 en HBM: public
