The signals acquired by the OPX using the analog input channels are first passed through an analog
input stage and then digitized. Here we discuss the voltage limits, gain and offset calibrations
that can be applied to the signal to be digitized.
The signal chain can be seen in Fig. 1. The signal source can be either AC or DC coupled.
Note
The OPX input has a common-mode voltage of 0.25V when measured with 50ohm.
DC coupled signal source
If the signal source is DC coupled and has 50ohm DC resistance to ground,
it can be directly connected to the analog input. This can be seen in Option 1
of Fig. 1
AC coupled signal source
If the signal source is AC coupled and does not have a 50ohm resistance to
ground, a bias T is needed in order to bias the input amplifier. The
required setup can be seen in option 2 of Fig. 1. In this case, the source
will still need to have a 50ohm AC impedance throughout its bandwidth for
proper operation.
The voltage gain can be set by adding a "gain_db" field to the "analog_inputs" field
of the controller in the config. Here we show an example with the relevant fields: