Elliptic IIR Filter (Digital Anti
-
Alias)
Passband
Stopband
Frequency [kHz]
δp: Passband ripple
δs: Stopband attenuation
ωp:
ωc:
Passband frequency
Corner frequency
Stopband frequency
ωs:
ωp=ωc ωs
Magnitude [dB]
1 + δp
1 - δp
δs
Figure A.245:
Digital Elliptic IIR Filter
When Elliptic IIR filter is selected, this is always a combination of the anti
-
alias filter built
-
in the Sigma Delta ADC and a digital Elliptic IIR filter.
Analog anti
-
alias filter
The Sigma Delta ADC anti
-
alias filter
Elliptic IIR filter
Characteristic
11
-
pole Elliptic style IIR
User selection
Auto tracking to sample rate divided by: 4, 10, 20, 40
User selects divide factor from current sample rate, software then adjusts filter when sample
rate is changed
Bandwidth (ωc)
User selectable from 2.5 Hz to 125 kHz
0.1 dB passband ripple (ωp)
DC to ωc. For ωc = 125 kHz, DC to 100 kHz due to amplifier bandwidth
When using the range
±
1 mV for ωc > 10 kHz, DC to 7 kHz due to amplifier bandwidth
Stopband attenuation (δs)
-
180 dB (
-
160 dB for
±
1 mV range)
Roll
-
off
-
100 dB/octave
Frequency [kHz]
Frequency [kHz]
Magnitude
[dB
]
Magnitude
[dB
]
100
Magnitude [%]
102.33
101.74
101.16
100.58
99.43
98.86
98.29
97.72
1000
100
10
1
0.1
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
Magnitude
[dB
]
±
1 mV Elliptic 125 kHz Overview
±
1 mV Elliptic 125 kHz Passband flatness
100
Magnitude [%]
102.33
101.74
101.16
100.58
99.43
98.86
98.29
97.72
1000
100
10
1
0.1
0.2
0.1
0
0.05
0.15
-0.1
-0.15
-0.05
-0.2
Frequency [kHz]
Magnitude
[dB
]
-160
-140
-120
-100
-80
-60
-40
-20
0
0.1
1
10
100
1000
±
10 V Elliptic 125 kHz Overview
±
10 V Elliptic 125 kHz Passband flatness
-160
-140
-120
-100
-80
-60
-40
-20
0
0.1
1
10
100
1000
Figure A.246:
Representative Elliptic IIR examples
(1)
Measured using Fluke 5730A calibrator, DC normalized
GEN3i
658
I3763-3.1 en HBM: public
