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2
SETTING UP THE ANALOG FRONT-END
2.1 ADQ8-4X AFE block diagram
The analog front-end setup for ADQ8-4X found in
, -
2# 3
.
/
0 1
#
DESCRIPTION
The analog input impedance 50 to GND
a
b
On ADQ8-4X-VG, the gain can be set in a discrete number of steps. By
requesting a certain range, the closest available setting is activated. The
actual range that is set is returned to the user. Note that the compensation
has to be done in the software.
Changing the input range requires a settling time of 1 s.
c
Set a DC offset for better using the signal range when the signal is
unipolar.
Changing the DC offset requires a settling time of 1 s.
d
The gain and offset is calibrated using a 32 MHz -1dBFS sine wave
signal. The digital compensation corrects the offset and the gain at this
frequency.
The user can access this block to set a different gain and offset. Note that
this is a digital gain and offset adjustment and not the same as selecting
analog input range in the –VG option.
Figure 3: AFE control.
2.2 Set analog input range
On ADQ8-4X–VG, the input range is variable. The requested input signal range is sent to the API,
which reads available settings and return the best selection. The actual value of each range is available
for calculations according to the following:
DESIRED_ANALOG_RANGE
ACTUAL_ANALOG_RANGE
The maximum digital code 2^15 represents an analog signal with a level
at the input. A specific analog signal
code:
DIGITAL_CODE_LEVEL = ANALOG_LEVEL / ( ACTUAL_ANALOG_RANGE / 2 ) * 2^15
19-2302 A
2020-09-16
&
-
-
(
01
is the requested range set into
is the actual calibrated range of the device returned from
ANALOG_LEVEL
Figure
3.
.
+
01
USER COMMAND
SetInputRange
SetAdjustableBias
SetGainAndOffset
SetInputRange
ACTUAL_ANALOG_RANGE / 2
will then be represented by the following digital
ADQ8-4X Manual
19-2302 A 2020-09-16
.
+
.
SetInputRange
9(46)
0 1
REF
2.2
2.3
2.4
.
(3)
9(46)
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