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 L.53:
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
Characteristic
Sigma delta, optimal frequency response
-
3 dB low pass bandwidth (ωlc)
100 kHz
±
5 kHz for sample rates 250 kS/s and 125 kS/s
80 kHz
±
5 kHz for all other sample rates
Elliptic IIR Filter
Characteristic
11
th
order 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)
100 Hz to 62.5 kHz
Stopband frequency (ωs)
Approximately 1.25 * ωc
0.1 dB passband flatness (ωp)
(1)
DC to ωc/1.5 or maximum 10 kHz
Stopband attenuation (δs)
80 dB
Frequency [kHz]
1000
100
10
1
0.1
Frequency [kHz]
Magnitude [dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
±1 V Elliptic IIR 62.5 kHz Overview
±1 V Elliptic IIR 62.5 kHz Passband flatness
±10 V Elliptic IIR 62.5 kHz Overview
±10 V Elliptic IIR 62.5 kHz Passband flatness
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
Frequency [kHz]
1000
100
10
1
0.1
Frequency [kHz]
Magnitude [dB]
-150
-130
-110
-90
-70
-50
-30
-10
10
Magnitude [dB]
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0
Magnitude [%]
2.33
1.74
1.15
0.57
-0.57
-1.14
-1.71
-2.28
1000
100
10
1
0.1
1000
100
10
1
0.1
Figure L.54:
Representative Elliptic IIR examples
(1)
Measured using Fluke 5700A calibrator, DC normalized
GEN3i
1106
I3763-3.1 en HBM: public
