UG-1308
Rev. A | Page 18 of 24
ADUCM355 SYSTEM CALIBRATION
Because of the complexity of the
number of voltage and current measurement channels on the
device, many calibration routines are implemented to ensure a
high level of measurement accuracy. This section describes the
main calibration functions with links to further online
information.
HIGH SPEED TIA GAIN RESISTOR CALIBRATION
The high speed TIA has three different programmable gain
resistor options.
Adjust the gain resistors to convert the current from the SE0, SE1,
and DE0 inputs or from the DE1 input to a differential voltage
across the R
TIA2
resistor, R
TIA2_03
resistor, or R
TIA2_05
resistor.
The R
TIA2
, R
TIA2_03
, and R
TIA2_05
resistors have an initial accuracy
range and vary with temperature, as specified in the
data sheet where R
TIA2
is the HPTIA R
TIA
gain resistor on the
SE0 and SE1 inputs, and R
TIA_02
and R
TIA_05
correspond to the
HPTIA R
TIA
gain on the DE0 and DE1 inputs.
If the high speed TIA is uncalibrated for the selected gain resistor
and the ADC programmable gain amplifier (PGA) setting, an error
is present when measuring an absolute input current.
To generate a precision calibration current, use the high speed
DAC to create a differential voltage across an external precision
R
CAL
resistor that is connected to the
and RCAL1 pin. The precision calibration current can be
routed through any of the three high speed TIA gain resistors.
Because the calibration current value is known and the ADC
can measure the voltage drop across the R
TIA2
, R
TIA2_03
, and R
TIA2_05
resistors, the exact R
TIA
resistor value can be determined.
Figure 33 to Figure 35 show the setup and switch settings that
connect the high speed DAC output to the external R
CAL
resistor so that the current flows into the high speed TIA and
R
TIA2
, R
TIA2_03
, and R
TIA2_05
gain resistors, respectively.
The
AD5940.c
file has a function that calibrates each gain
resistor for the HSTIA. For further details on how to use this
function, visit
https://wiki.analog.com/resources/eval/user-
guides/eval-ad5940/calibration_routines/hstia_cal?doc=EVAL-
ADuCM355QSPZ-UG-1308.PDF