HBM Genesis GEN5i User Manual page 419

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
Analog anti aliasing filter characteristic
Bessel IIR filter characteristic
Bessel IIR filter user selection
Bessel IIR filter bandwidth (ωc)
Bessel IIR passband flatness (ωp)
Bessel IIR filter stop band attenuation (δs)
Bessel IIR filter roll-off
(1) Measured using Fluke 5700 calibrator, DC normalized
I2679-4.0 en
Figure A.62: Digital Bessel IIR Filter
220 kHz ± 20 kHz (-3 dB)
7-pole Bessel, optimal step response
6-pole Bessel style IIR
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
Auto tracking the sample rate with the selected Bessel IIR filter user selection from
0.0125 Hz to 100 kHz
(1) 0.1 dB; DC to 20 kHz @ ωc = 100 kHz
-60 dB
With Bessel IIR filter bandwidth selection ωc = 100 kHz a peak at -55 dB will occur between
500 kHz and 1 MHz due to limited analog anti alias filter amplitude reduction. At lower
bandwidth selections the digital filter will reduce this peak to -60 dB
-36 dB/Octave
Figure A.63: Typical Bessel IIR ωc = 100 kHz, Overview and passband flatness
GEN5i
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