PXI vst 5645r gain / attenuation calibration RX TX chain

[gottardo.giuseppe]

Hello,

I am working with PXI vst 5645r. I am doing some research using the RF output of transmitter connected with the RF input of receiver.

In my application it is important to know the equivalent attenuation and gain that I get from the generation (output of DAC) up to the acquisition (input of ADC) (loop gain).

I looked http://zone.ni.com/reference/en-XX/help/373680C-01/vstdevices/5645_analog_input/ and http://zone.ni.com/reference/en-XX/help/373680C-01/vstdevices/5645_analog_output/ in order to understand better how is built the structure of my channels.

Together I looked in the design in labview how these parameters are controlled and set (example VST streaming (Host)). I found just the configuration of gain for the transmitter in the block "LO_cal" but I didn't see any calculation for the various attenuations of transmitter. I have still to check these datas for the transmitter.

How are controlled and set all this parameters in the transmitter and receiver normally?

I guess the receiver chain attenuates the signal in order to use the maximum dynamic range od ADCs and to use the right power input of demodulator... does the calibration change gain/attenuation values in the receiver chain every time I use a different gain (peak power dbm) in the transmitter?

Thanks in advance

Best regards

Giuseppe

[DesasterMaster]

Hi Guiseppe,

so you have already checked the getting started guide and the specifications?

Manual PXIe-5645R

Geting Started Guide PXIe-5645R

Here you can find the Hardware Architecture of the PXIe-5645R:

Hardware Architecture of PXIe-5645R

And the Software Architecture as well:

Software Architecture of PXIe-5645R

The Hardware Architecture should clearify your questions.

Best wishes

Dennis

[gottardo.giuseppe]

Hello Dennis,

thanks for your answer.

I have already read all this documentation but there are still some open questions:

what is exactly the "reference level" of the receiver in the VST example?

I went through all the calibration details in the VST streaming example and I got all the calibration values of attenuations and gains through the tx and rx chains for different output TX power values.

I have all the values of gain and attenuations of these schemes: http://zone.ni.com/reference/en-XX/help/372058N-01/vstdevices/5645_analog_output/ and http://zone.ni.com/reference/en-XX/help/372058N-01/vstdevices/5645_analog_input/. Where is placed the upconverter/downconverter gain in this pictures?

In VST example what is exactly the upconverter and downconverter gain?

which are the output power of DAC and the input power of ADC? how are they related to the calibration of TX and RX chain?

I would like just to calculate the equivalent loop gain from the DAC output to the ADC input.

Best regards

Giuseppe

PS: in the documentation you sent me there are no details about calibrations and how the parameters are related one to each other....

[DesasterMaster · Accepted solution]

The Reference Level is a "guide" for the VST driver to set the attenuators and gain so that the range of the ADC/DAC are used at the best.
Depending of the frequency you are and the reference level you choose, the VST driver will look at the best combination of attenuations

and gain to get the Signal arriving to the ADC to use his full range:
You can see the calculations in this niRFRIO Group A Config 1.0.0 Shared Private.lvlib:Select Calibrated RF In Gain.vi

This Gain is the "Downconverter Gain" which summarize the whole path of Rf In.

So practicall the Downconverter/Upconverter Gain is the total analog gain which is put on the signal just before/after the ADC/DAC.
This is done in the niRFRIO GRoup A Config 1.0.0 Shared Private.lvlib:Select Calibrated RF In Gain.vi.

The Find Gain Index find scan all possible Power levels for this frequency and get the nearest level to the choosen reference level.

Whith this informations he knows which attenuators and gain he has to set to reach the get power at its best to the ADC (input gain settings)

So to calculate the loop gain, you should set a fix refeerence level so that all attenuations and gain in both paths stay fixed, test it with a calibrated CW and then use this configuration for your DUT.

When you read the IQ from the VST (Fetch Single Record) this informations is passed to the function so it can calculate the ADC values and calibrated them back to actual value on RF In:

If you calculate the loop gain inside the FPGA then you have to send the downconverter/upconverter gain informations from the host to the FPGA. You can then use there this informations to calculate the loop gain.

Best wishes

[gottardo.giuseppe]

Thanks for your answer.

In this days looking at the design I made the same conclusions.

I have just another question.

You wrote "So practicall the Downconverter/Upconverter Gain is the total analog gain which is put on the signal just before/after the ADC/DAC."

So the DAC digital I/Q gain is not included in the upconversion gain right? Looking at the picture here below the DAC digital gain is added after at the upconverter gain.

 

If I am right, in order to calculate the loop gain I have just to take into account:

DAC digital gain + upconverter gain + downconverter gain (+ DUT gain/attenuation). right?

Is there any other digital gain for the receiver path noth included in the downconverter gain?

Thanks

Best regards

Giuseppe Gottardo