Analog to Digital Conversion
Sample rate per channel
1 S/s to 25 MS/s
ADC resolution; one ADC per channel
14 bit
ADC Type
CMOS pipelined multistep converter, LTC2254
Time base accuracy
Defined by mainframe:
±
3.5 ppm
(1)
; aging after 10 years
±
10 ppm
Binary sample rate
Not supported
Maximum binary sample rate
N/A
External time base sample rate
0 S/s to 10 MS/s
External time base level
TTL
External time base minimum pulse width
50 ns
(1)
Mainframes using Interface/Controller modules shipped before 2012:
±
30 ppm
Anti
-
Alias Filters
Using different filter selections (Bessel/Bessel IIR) or different filter bandwidths can result in phase mismatches between channels.
Flash ADC
Sample Rate Selection
Analog Input
Digital Filter (Anti-Alias)
1 out of N
A
F
Analog Anti-Alias Filter
1010
A
F
y
(n)
n
-1
n
-1
Σ
x
(n)
z
-1
z
-1
Figure A.62:
Combined analog and digital anti
-
alias filter block diagram
Anti
-
aliasing is prevented by a steep, fixed frequency analog anti
-
alias filter in front of the Analog to Digital Converter (ADC). The ADC always
samples at a fixed sample rate. The fixed sample rate of the ADC avoids the need for different analog anti
-
alias filter frequencies.
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 supports a range of fixed bandwidth anti
-
alias filters. 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.
Bessel (Fc @
-
3 dB)
The Bessel anti
-
alias filter is always enabled. This filter only protects anti
-
aliasing for the
100 MS/s ADC over sampling. The digital Bessel IIR filter must be used to prevent aliasing
at the selected sample rates. Bessel filters are typically used when looking at signals in the
time domain. They are best used for measuring transient signals or sharp edge signals like
square waves or step responses.
Using the Bessel filter, enhanced resolution is not supported at lower sample rates.
Bessel IIR (Fc @
-
3 dB)
When Bessel IIR filter is selected, this is always a combination of an analog Bessel anti
-
alias filter and a digital Bessel IIR filter to prevent aliasing at lower sample rates.
Bessel filters are typically used when looking at signals in the time domain. They are best
used for measuring transient signals or sharp edge signals like square waves or step
responses.
Enhanced resolution is supported by using over sampling combined with a digital filter at
the following sample rates: 15 bit resolution at 25 MS/s and lower, 16 bit resolution at
10 MS/s and lower.
GEN3i
I3763-3.1 en HBM: public
455
