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2. Align ET System

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. This can be achieved by performing normal envelope tracking. Refer to Example ET Measurement to know how to handle the envelope tracking to finish the alignment of ETPS output and RF signal. This is must before making meaningful PAE measurement.

There are two methods:

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

• 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.

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

Figures 1 and 2 show the DPD results before and after alignment respectively.

Figure 1. DPD result before Alignment

Figure 2. DPD result after auto-Align