HBM Genesis GEN5i User Manual page 421

FIR (Fc @ -3 dB) filter
When FIR (Fc @ -3 dB) filter is selected, this is always a combination of an analog Butterworth anti alias filter and a digital FIR (Fc @ -3 dB)
filter. Adapted FIR filter with ωp reduced by a factor of ≈1.4 compared to the FIR (Fc @ -0.1 dB) filter. Supported by Perception V6.40 and
higher.
Analog anti aliasing filter bandwidth
Analog anti aliasing filter characteristic
FIR (Fc @ -3 dB) filter characteristic
FIR (Fc @ -3 dB) filter user selection
FIR (Fc @ -3 dB) filter bandwidth (ωc)
FIR (Fc @ -3 dB) filter passband flatness (ωp)
FIR (Fc @ -3 dB) filter stopband attenuation (δs)
FIR (Fc @ -3 dB) filter roll-off
Figure A.67: Typical FIR (Fc @ -3 dB) ωc = 250 kHz, Overview and passband flatness
(1) Measured using Fluke 5700 calibrator, DC normalized
I2679-4.0 en
Figure A.66: Digital FIR (Fc @ -3 dB) filter
370 kHz ± 20 kHz (-3 dB)
7-pole Butterworth, extended passband response
12-pole FIR; FIR is a pure digital characteristic. Closest analog resemblance to elliptic filters,
however FIR has both overshoot on step response and pre-shoot to step response. This
means ringing on the signal starts before the step input starts and the ringing continues
after the step input ends.
Auto tracking to sample rate divided by: 4, 10, 20, 40
Divided by 40 not available for 1 MS/s & 500 kS/s sample rate
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 FIR (Fc @ -3 dB) filter user selection from
0.031 Hz to 250 kHz
0.1 dB; DC to ≈ωc/1.4 (Adapted FIR filter behavior)
(1)
0.1 dB; DC to 125 kHz; FIR (Fc @ -3 dB) filter bandwidth selection ωc = 250 kHz, limited
by the 370 kHz analog anti alias filter amplitude response. All other bandwidth selections
not affected
-60 dB
With FIR (Fc @ -3 dB) filter bandwidth selection ωc = 250 kHz a peak at -35 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
-72 dB/Octave
GEN5i
421