Archived: Adjusting the PXIe-5622 Amplitude Response

Publish Date: Apr 03, 2019 | 1 Ratings | 4.00 out of 5 | Print | Submit your review

Overview

This document has been archived and is no longer updated by National Instruments.

This example uses the LabVIEW Digital Filter Design Toolkit to create an equalization filter to optimize the flatness of the amplitude response of the NI PXIe-5622 High-Speed Digitizer.

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Equalization_Filter.zip includes two files, NI 5622 Calibration.llb and niScope EX OSP Downconversion with Flatness Calibration.vi.

The first file is a library which contains “Apply Frequency Response Compensation.vi”, the VI required to equalize the amplitude response of your NI PXIe-5622, and all of its dependencies.  The second file is an example which demonstrates how to use the Apply Frequency Response Compensation VI within your NI-Scope Onboard Signal Processing (OSP) application.

Leveraging the Example for Your Application

The VI, “Apply Frequency Response Compensation.vi”, is shown in Figure 1.  

Figure 1: Apply Frequency Response Compensation Sub VI

You can set the “bandwidth” and “center frequency” inputs to optimize the flatness over a specific frequency range of interest or leave the default values (-1) to calibrate the entire bandwidth of the device.  The VI can be enabled or disabled to turn the equalization filter on and off using the input “apply flatness”.  By setting “cache” to true, the VI will optimize the efficiency of the application by only recalculating the coefficients when a configuration setting has changed.   

The VI calculates the normalized gain of the resulting filter.  This value is then inverted and returned as the output “gain”.  The “gain” should be applied to your data to scale it to its correct amplitude.

Performance Improvements After Equalization

Figures 2 & 3 show the before and after response of the Bandpass and Direct paths, which demonstrate how setting an equalization filter can greatly improve your response to achieve optimal measurements.


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Figure 2: Amplitude Response of NI PXI-5622 (Bandpass Path) before and after setting Equalization Filter

 


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Figure 3:  Amplitude Response of NI PXI-5622 (Direct Path) before and after setting Equalization Filter

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