Analog to Digital Conversion
Sample rate; per channel
1 S/s to 20 kS/s
ADC resolution; one ADC per channel
24 bit, only 16 bit recorded
ADC type
Sigma Delta (Σ
-
Δ) ADC; Analog Devices AD7764BRUZ
Time base accuracy
Defined by mainframe:
±
3.5 ppm
(1)
; aging after 10 years
±
10 ppm
Binary sample rate
Supported; produces rounded BIN values when calculating FFT's
Maximum binary sample rate
20.48 kS/s
External time base frequency
0 S/s to 20 kS/s
External time base frequency divider
Divide external clock by 1 to 2
20
External time base level
TTL
External time base minimum pulse width
200 ns
(1)
Mainframes using Interface/Controller modules shipped before 2012:
±
30 ppm.
Anti
-
Alias Filters
Using different filter selections (Wideband/Bessel IIR/Butterworth IIR) or different filter bandwidths can lead to phase mismatches between
channels.
Sample rate selection
Digital Filter (Anti-Alias)
A
F
y
(n)
n
-1
n
-1
Σ
x
(n)
z
-1
z
-1
Anti-Alias Sigma Delta ADC
1010
Analog input
A
F
1 out of N
Figure L.65:
Combined analog and digital anti
-
alias filter block diagram
Anti
-
aliasing is prevented by a steep, fixed frequency analog anti
-
alias filter integrated inside the Sigma Delta Analog to Digital Converter (ADC)
always sampling at a fixed sample rate. This setup avoids the need for other analog anti
-
alias filters.
Directly behind the ADC, the high precision digital filter is used as anti
-
alias protection before the digital downsampling to the desired user
sample rate is performed. The digital filter is programmed to a fraction of the user sample rate and automatically tracks any user sample rate
selection. Compared to analog anti
-
alias filters, the programmable digital filter offers additional benefits like higher order filter with steep roll
-
off, a larger selection of filter characteristics, noise
-
free digital output and no additional phase shifts between channels that use the same filter
settings.
Sigma Delta Wideband
When Sigma Delta wideband is selected the built
-
in anti
-
alias filter of the Sigma Delta ADC
(no digital filter) is always in the signal path. Therefore, the anti
-
alias protection is always
active when Sigma Delta wideband is selected.
Bessel IIR
When Bessel IIR filter is selected, this is always a combination of the built
-
in anti
-
alias filter
of the Sigma Delta ADC and a digital Bessel IIR filter.
Bessel filters are typically used when looking at signals in the time domain. Best used for
measuring transient signals or sharp edge signals like square waves or step responses.
Butterworth IIR
When Butterworth IIR filter is selected, this is always a combination of the built
-
in anti
-
alias
filter of the Sigma Delta ADC and a digital Butterworth IIR filter.
Best used when working in the frequency domain. When working in the time domain this
filter is best used for signals that are (close to) sine waves.
GEN3i
I3763-3.1 en HBM: public
1125
