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3. Executing the Measurement and Viewing Results

This section introduce how to execute the envelope tracking test and how to view the measurement results. Follow the procedure below to execute the measurement and view the measurement results.

Initial Run

Timing Alignment

Executing the Measurement

Viewing the Measurement Results

Initial Run

1. Click the Run button on the tool bar to get the RF and ET waveform downloaded into the instrument and get the initial measurement results.

   

2. Once the measurement begins, the detailed information will be displayed in the Log view at the bottom of the window as shown below.

   

   During the running process, you can stop it any time by clicking the Stop button. When you see the "Complete!" message in the Log view, it indicates that the measurement is completed.

   

Timing Alignment

Timing alignment is to synchronize the input signal of the PA (the output of the RF Signal Generator) with the input voltage of the PA (the output of the Envelope Signal Generator) in time domain. There are two methods:

• Manual: Adjust the Delay and Step setting in Envelope Tracking block manually with an oscilloscope connected to the Envelope Signal Generator and RF Signal Generator and observe the signals alignment. Perform the following steps:

  1. Reset the delay value to zero if rough delay of system is unknown.
     

  2. Perform envelope tracking (does not matter if DPD is enabled or not) operation to make it pass. This is the precondition of manual envelope tracking alignment. The SYNC MARK OUT, PA Out and ETPS Out signals can be viewed on the oscilloscope.

  3. Choose the right rough horizon resolution on the oscilloscope to make the display stable and calculate the rough delay time. For example, ETPS Out signal has a rough delay time of 16000 nsec relative to the RF signal which can be calculated using a simple oscilloscope measurement as shown in the figure below.
     
     

  4. The time delay of -16000 nsec is used to make a first rough alignment by updating the delay value to -16000 as shown in the figure below. After this step, the ETPS Out signal and RF signal can be roughly aligned (see below graph).
     
     

  5. After ETPS Out and RF signals are roughly aligned, change the delay value to a smaller valuer to get a fine aligned envelope tracking system.
     

  6. In case you do not have an oscilloscope, use the auto-alignment button to get the signals aligned automatically.
• Auto: Click the Auto-align ET and RF signals button on the tool bar to get the signals aligned automatically.

  

  By selecting the Pre-Align with AM-AM for Auto-Align check box in the Envelope Tracking block, you can find a possible better initial delay value with the measured AM-AM results, but this may take longer time. After the auto-alignment is finished, the Delay setting in Envelope Tracking block is updated automatically.

Once sample rate related setting changed, or M8190 was reset manually, the relative timing between envelope signal and RF signal signal will become unknown and unstable, “run” action and “align” action must be repeat again.

If the related settings (e.g. sample rate, IQ delay, trigger delay in Generator instruments, etc.) are changed and applied, it is recommended to do the timing alignment again.

Executing the Measurement

Once a proper time alignment has completed, the signal can be played repeatedly without re-alignment. Click the Run button to play the signal and get the measurement results.

Viewing the Measurement Results

In the measurement view, there are four result windows: AM-AM, AM-PM, ACP, and EVM vs. Power. EVM vs. Power results are displayed only when Power Sweeping (in PA block) is set to On.

For ET test, ACP results are viewed. To view more detailed information, double-click on the ACP window to enlarge it as shown in the figure below.

Figure 1. ACP Results

Depending on the test scenario, the envelope signal output for M8190A can vary. However, the M8190A output amplitude varies with the offset value, so it is important to pay attention and check if the M8190A (envelope signal generator) output has been clipped.

If the signal analyzer fails to wait for triggering, there can be two possible reasons:

1. The trigger signal cable may not be well connected;

2. The trigger level is not appropriate because of the possible BNC divider used in the system connection

In both the cases, the trigger level adjustment is needed.