Self-Calibration of NI Vector Signal Analyzers and Vector Signal Generators
The easiest way to perform a self-calibration on NI Vector Signal Analyzers and Generators is to use the device’s Soft Front Panel (RFSA or RFSG Soft Front Panels) as seen in Figure 2 below. The Self Calibration button can be found in both soft front panels by navigating to Device/System >> Calibration. In the case of the PXIe-5644R/5645R/5646R, the Self Calibration button in the Soft Front Panels performs a partial self-calibration. Partial calibration is discussed in more detail later in this article.
Figure 2. Self-calibrating through the NI-RFSA Soft Front Panel
Additionally, for Vector Signal Analyzers and Vector Signal Generators (excluding the PXIe-5644R/5645R/5646R) self-calibration can be performed through the NI-RFSA and NI-RFSG LabVIEW API’s respectively using the niRFSA Self Cal VI or niRFSG Self Cal VI. This can also be performed in C using the niRFSA_SelfCalibrate and niRFSG_SelfCalibrate functions.
Note: Most of the LabVIEW calibration functions are also available in C. There is a link to the C Function Reference for calibration functions in the Related Links section below.
Figure 3. niRFSA Self Cal VI is used to perform Self-calibration
For multi-module analyzers and generators such as the PXIe-5668R or PXIe-5673E, module specific self-calibration can be performed in NI Measurement and Automation Explorer (NI MAX). Module specific self-calibrations can also be done through the driver; however, a full self-calibration of the system may still be required. The niRFSA Is Self Cal Valid VI can be used to determine if there is valid self-calibration data on the device. It also returns an array of valid steps that can be directly provided to the steps to omit input of the niRFSA Self Cal VI. Omitting steps is discussed in the next section.
Figure 4. niRFSA Is Self Cal Valid VI is used to determine if self-calibration is needed
Omitting Self-Calibration Steps on Vector Signal Analyzers
Omitting steps allows the user to decrease the time of self-calibration by targeting specific sub-systems of the device. Each Vector Signal Analyzer device is different in the steps it performs during self-calibration. For each module, a list of specific steps that can be omitted can be found in the device specific section of the NI-RFSA Help documentation. For instance, the PXIe-5668R self-calibrates the following parameters:
- Preselector alignment
- IF flatness
- Gain reference
- LO self-calibration
The niRFSA Self Cal VI provides an array input for omitting steps. As mentioned above, not all step options apply to every analyzer. If any of the steps specified to omit are not supported by the analyzer, the driver will return an error.
Figure 5. Omitting Steps on the RFSA Self-Calibration Process
It should be noted that omitting steps can invalidate self-calibration data which in turn causes associated specifications to not be guaranteed. Conversely, omitting valid steps does not invalidate any specifications.
Self-Calibration of NI Vector Signal Transceivers
The Vector Signal Transceivers (VST’s) can be self-calibrated using the NI-RFSA Soft Front Panel and NI-RFSG Soft Front Panels. Additionally, the niVST Self Calibrate VI in the VST Instrument Design Libraries (IDL) API can be used.
In addition to the options described, there is a specific utility included in the NI-RFSA, NI-RFSG, and the VST IDL driver installations that can be used to calibrate the NI PXIe-5644R/5645R/5646R devices. The utility can be found in Windows by navigating to Start>>All Programs>>National Instruments>>Vector Signal Transceivers>>VST Self Calibrate.
Partial Self-Calibrate Range
Additionally, NI Vector Signal Transceivers feature the ability to perform a partial self-calibration. Partial self-calibration allows the user to perform self-calibration on only the necessary frequency and reference level ranges required for the application. It is also possible to choose which types of corrections to apply by omitting steps that are not required for the application. This allows the user to tailor the self-calibration to their specific application. Data from a partial self-calibration is not stored on the VST’s FLASH memory as it is for a normal self-calibration. Instead, it is stored in the kernel device memory and consequently this data is lost on reboot.
Partial self-calibration takes a fraction of the time of a full self-calibration. This minimizes the time and the temperature drift between the partial self-calibration and measurement which in turn improves measurement accuracy.
There are two ways to perform a partial self-calibration. Since the VST has both an analyzer and a generator, niRFSA RF In Self-Calibrate Range VI and niRFSG RF Out Self-Calibrate Range VI can be used to perform partial self-calibration on each respectively. Alternatively, niVST RF In Self Calibrate Range VI and niVST RF Out Self Calibrate Range VI can be used when working from the open FPGA sample projects.
Note: You can also omit steps as part of a partial calibration as described previously.