Digital FIR (Fc @
-
0.1 dB) Filter (Digital Anti
-
Alias)
ωp = ωc ωs
Passband
Stopband
δp : Passband ripple
δs : Stopband attenuation
ωp
ωc
ωs
: Passband frequency
: Corner frequency
: Stopband frequency
Frequency [kHz]
Magnitude [dB]
δs
1 + δp
1 - δp
Figure A.47:
Digital FIR (Fc @
-
0.1 dB) filter
When FIR (Fc @
-
0.1 dB) filter is selected, this is always a combination of an analog Butterworth anti
-
alias filter and a digital FIR filter
Analog anti
-
alias filter
Characteristic
7
-
pole Butterworth, extended passband response
Bandwidth
140 kHz
±
20 kHz (
-
3 dB) All Ranges < 100 mV
350 kHz
±
20 kHz (
-
3 dB) All Ranges ≥ 100 mV
Digital FIR (Fc @
-
0.1 dB) filter
Characteristic
12
-
pole FIR; FIR is a purely digital characteristic. Its closest analog resemblance is to an
Elliptic filters. However, FIR has both ringing on the signal before the step input is started
and ringing after the step input is complete.
User selection
Auto tracking for 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, software then adjusts filter when sample rate is changed
Bandwidth (ωc)
User selectable from 0.031 Hz to 250 kHz
0.1 dB Passband flatness (ωp)
(1)
DC to ≈ωc
DC to 60 kHz; bandwidth selection ωc = > 50 kHz, limited by the analog anti
-
alias filter
amplitude response.
For all Ranges < 100 mV, ωp is limited to 10 kHz due to an anti
-
alias filter.
Stopband attenuation (δs)
60 dB; with filter bandwidth selection of ωc = 250 kHz, a peak of
-
35 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.
Roll
-
off
72 dB/Octave
1000
100
10
1
0.1
Magnitude [dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Frequency [kHz]
Magnitude [dB]
Frequency [kHz]
10000
1000
100
10
1
0.1
± 20 mV
FIR (Fc @ -0.1dB) 250 kHz Overview
± 20 mV
FIR (Fc @ -0.1dB) 250 kHz Passband flatness
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
1000
100
10
1
0.1
Magni
tude
[dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Frequency [kHz]
Magni
tude
[dB]
Frequency [kHz]
10000
1000
100
10
1
0.1
±1 V
FIR (Fc @ -0.1dB) 250 kHz Overview
±1 V
FIR (Fc @ -0.1dB) 250 kHz Passband flatness
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0
0
Magni
tude
[%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Magnitude
[%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Figure A.48:
Representative FIR examples
(1)
Measured using a Fluke 5700 calibrator, DC normalized
GEN3i
I3763-3.1 en HBM: public
427
