Digital IF Equalization

Digital IF equalization is a calibration that involves measuring and then compensating for IF magnitude and phase response.

IF equalization calibration gives the PXIe-5668 the ability to measure lower levels of error vector magnitude (EVM). For spectrum measurements, IF equalization results in a higher degree of magnitude accuracy across the IF bandwidth.

To achieve the desired IF flatness and overall accuracy specifications, equalization must be performed. Equalization attempts to correct for the following factors:

  • Frequency response of the digitizer
  • RF response of the downconverter
  • IF response of the downconverter

To enable digital IF equalization, use either the Digital IF Equalization Enabled property or the NIRFSA_ATTR_DIGITAL_IF_EQUALIZATION_ENABLED attribute.

Supported Configurations for Digital IF Equalization

Refer to the following table for PXIe-5668 device configurations that support digital IF equalization.

FPGA Image Filter Path Equalization Supported
400 MHz 400 MHz (765 MHz filter) Yes
320 MHz
100 MHz
5 MHz (I/Q rates >7.8125 MHz) Spectrum mode only. Data is unequalized in I/Q mode.
5 MHz (I/Q rates ≤7.8125 MHz) Yes
300 kHz Spectrum mode only. Data is unequalized in I/Q mode.
800 MHz 765 MHz Yes
320 MHz
100 MHz Spectrum mode only. Data is unequalized in I/Q mode.
5 MHz
300 kHz
Note For the 100 MHz path, NI-RFSA automatically performs digital IF equalization using the appropriate response. If you use an external digitizer, perform an I/Q acquisition using the 300 kHz filter path, or set the Digital IF Equalization Enabled property or the NIRFSA_ATTR_DIGITAL_IF_EQUALIZATION_ENABLED attribute to FALSE, NI-RFSA does not perform IF equalization on the acquired data. However, you can retrieve the appropriate response data and then use the response data to manually correct the acquired data. You can retrieve various forms of the IF response and RF response using the niRFSA Get Frequency Response VI or the niRFSA_GetDeviceResponse function.
Note For the PXIe-5668, the preselector is not part of the IF filter path, so NI-RFSA does not equalize the preselector distortions.