2. Configuring Parameters in the N7614B Software

The following figure shows the block view settings in N7614B for DPD measurement. In this example, the Envelope Tracking block is turned Off.

The remaining section of this topic provides an example procedure of setting N7614B for DPD measurement. Note that for different PA, the settings are different.

Step 1: Set the Waveform Block

Step 2: Set the Crest Factor Reduction Block

Step 3: Set the Digital Predistortion Block

Step 4: Set the RF Signal Generator Block

Step 5: Set the PA Block

Step 6: Set the Signal Analyzer Block

Step 7: Set the Measurement View

Step 1: Set the Waveform Block

Click on the Waveform block icon on the UI. In the right panel, do the following:

  1. Select Preloaded as the Waveform Type and select the "LTE_FDD_5M_QPSK_FullRB.wfm" file.

    ClosedWaveform Settings
    If you want to use a waveform generated by another Keysight signal studio, set Waveform Type to Signal Studio and select the file. Refer to Creating and Exporting Waveforms for details about exporting a waveform file.
    Note that to use a waveform generated by another signal studio software for DPD test, the instrument needs to have the corresponding license. For this example, to use LTE waveform, the N7624B license needs to be installed in the instrument.

  2. Set the Bandwidth to 5 MHz according to the waveform bandwidth.

  3. Set the Resampling Ratio to 3.

    To extract the DPD model, it is expected that the oversampling ratio of the waveform is no less than 3. If the selected waveform has less oversampling ratio, you can set the oversampling ratio. For example, if the oversampling ratio for the original waveform is 2, and the oversampling ratio here is set to 3, then the final oversampling ratio will be 6, which is sufficient to perform DPD measurement.

Step 2: Set the Crest Factor Reduction Block

Click on the Crest Factor Reduction block icon and Closedturn Crest Factor Reduction to Through on the UI.

Step 3: Set the Digital Predistortion Block

Click on the Digital Predistortion block icon and Closedturn on Digital Predistortion on the UI. In the right panel, do the following:

  1. Select Extract and Apply as the DPD Mode.

    Two modes are supported to perform the digital predistortion.

    • Extract and apply is to extract the PA model using the signals captured by the Signal Analyzer, so there will be a Closedfeedback line from the Spectrum Analyzer block to the Digital Predistortion Block on the block diagram.

  2. Set the Number of Iteration to 1. By setting this parameter, the extraction model will be repeated by feeding its output to the input to minimize error. Typically, setting it to 3 is enough.

  3. Set the PA Model Type to Look-up Table. Refer to DPD Concept for details about different PA model types.

  4. Set the LUT Size to 128, AM/AM Polynomial Order to 5, and AM/PM Polynomial Order to 5.

Different PAs may have different characteristics, which will need different DPD models to simulate the DPD performance. In DPD test, if the measurement results are not as expected, you can try to change the the parameters for DPD model extraction. If the DUT is memoryless, it is recommended to set the PA Model Type to Look-up Table, or to set the PA Model Type to Memory Polynomial or Volterra Series and set the Memory Order to 0 or 1. If the DUT is memory device, it is recommended to set the PA Model Type to Memory Polynomial or Volterra Series.

Step 4: Set the RF Signal Generator Block

Click on the RF Signal Generator block icon on the UI. In the right panel, do the following:

  1. Enter the IP address or host name of the RF Signal Generator and the toggle the Closedconnect button on the top of the window to Connected state. After the instrument is connected, the model number and serial number of the instrument will be displayed in the Instrument cell.

  2. Set Frequency to 5.18 GHz.

Step 5: Set the PA Block

Click on the PA block icon on the UI. In the right panel, do the following:

  1. Enter the PA information by setting the Loss In, Loss Out, and PA Gain.

  2. Select PA Output as the Power Mode and set Power Servo to On.

    After turning on the Power Servo, N7614B Signal Studio for Power Amplifier Test will adjust the output power of the RF Signal Generator according to the power received by the Signal Analyzer to make sure the PA output power is close to the specified value.

  3. Set Power to 17.00 dBm and Power Tolerance to 1 dB. This is to set the output power of the PA and the accuracy of the power servo.

    The initial Amplitude setting in RF Signal Generator block will be set to (Power - PA Gain + Loss In) automatically.

    When the output power level of the RF Signal Generator is high, the DPD model extracted is a combination of the RF Signal Generator and the DUT.

Step 6: Set the Signal Analyzer Block

Click on the Signal Analyzer block icon on the UI. In the right panel, do the following:

  1. Enter the IP address or host name of the Signal Analyzer and the toggle the Closedconnect button on the top of the window to Connected state. After the instrument is connected, the model number and serial number of the instrument will be displayed in the Instrument cell.

  2. Note that the Frequency value is coupled to the frequency setting in RF Signal Generator block.

  3. Set the Trigger Source to External 1 and adjust Trigger Delay value as needed. For most cases, you can use the default value.

Step 7: Set the Measurement View

Click the button on the ClosedUI to change the current view from block view to measurement view.

You can turn Intermediate Result to On and set the ACP parameters as required. In this example, the default settings are used.