Real Time

Using Envelope Tracking

Envelope tracking (ET) enables you to build, import, and manage multiple shaping tables that can be used to change the power supply voltage levels of a power amplifier (PA), according to the behavior of the RF signal's envelope. This allows you to test PAs for improved battery efficiency and signal quality (i.e. increase output power, reduce distortions, and improve linearity). This system overview diagram shows how the Signal Studio's envelope tracking control helps you perform ET testing efficiently.

The remaining sections of this topic together provide an example procedure for using Signal Studio's envelope tracking control.

• System Configuration

• Step 1: Verify IQ Waveform

• Step 2: Manage Envelope Shaping Tables

• Step 3: Generate and Shape the Envelope Signal

• Step 4: Mange Arbitrary Waveform Generator (AWG) for Envelope Generation

• Step 5: Specify Frequency and RF Power

• Step 6: Adjust AWG Output Settings

• Step 7: Generate Signals and Adjust Timing

System Configuration

The ET system used in the following example procedure is comprised of the following:

• PC running the Signal Studio software

• N5172B/82B MXG RF vector signal generator

• 33521A/22A, 33521B/22B, or 33621A/22A arbitrary waveform generator

Connect the equipment as shown below.

Step 1: Verify IQ Waveform

1. Click the IQ Waveform block.

2. Click the Generate Waveform icon to view spectrum and CCDF curve.

Step 2: Manage Envelope Shaping Tables

1. Click the Shaping Table Manager block.

2. In this window, you can do the following:

• Select and apply a shaping table

• Create new shaping tables

• Assign a unique name to a shaping table

• Edit the currently selected shaping table

• Import and export shaping tables as CSV files

3. Make sure you select (highlight) the table you want to apply before going to next step.

Step 3: Generate and Shape the Envelope Signal

1. Click the |X| and Transformation block.

2. In the parameter view, set the Oversampling ratio for the Envelope Data. Higher sample rates produce smoother envelope traces, but use more arbitrary memory space and increase bandwidth.

3. Click the Generate Envelope Data button.The shaping table you selected in the previous step will now be applied to the generated envelope data.

4. Compare envelopes before (green) and after (yellow) applying the shaping table. The envelope graph shows only the beginning portion of the entire waveform, so it may not include the largest peak point. Maximum and minimum peak envelope voltage is shown at the top of the graph.

5. Set the Conversion Input Type. Choices include the following:

   • Absolute RF Output Voltage: Use RF output voltage value as conversion table x-axis value. If RF output amplitude is changed, converted data may be changed.

   • Normalized RF Output Voltage: Use normalized power value of IQ waveform data as conversation table x-axis value. Value range is 0 – 1, so that the 0 – 1 range of x-axis are always used for the conversion. RF output amplitude does not affect the conversion.

   • Override Absolute RF Output Voltage: Apply fixed value (not linked to RF output voltage). Fixed value is provided in the Power for transformation input parameter.

6. Set the Power for transformation input. This value is used for the rms power level of RF signal for transformation input instead of RF output voltage from RF signal generator amplitude. This parameter appears only when the Conversion Input Type is set to Override Absolute RF Output Voltage.

7. Set the Pre Conversion Filter. Applies a band-limiting, low-pass filter (LPF) to the envelope. Bandwidth can be arbitrarily specified from 1 MHz to 200 MHz. The LPF becomes pass-through when the LPF bandwidth is greater than half of the envelope sample clock.

Step 4: Mange Arbitrary Waveform Generator (AWG) for Envelope Generation

1. Click the Envelope Signal Generator block.

2. Enter the address for the AWG and click the Check Connection button.

3. Specify voltage range and limits to protect ETPS input. Output Limit State must be set to On for limit settings to work.

4. Set the Output Load impedance: 50 Ohm, 100 Ohm, or High-Z.

5. For differential operation, select Inverted for Dual Channel Operation. Dual channel operation requires a 33522A/B.

Step 5: Specify Frequency and RF Power

1. Click the RF Signal Generator block.

2. Set RF frequency, amplitude, and other parameters.

3. Configure trigger settings.

   Default setting for Continuous is set to Free Run.

   To Trigger with external trigger input:

   • Set Trigger Source to External

   • Set Continuous to Trigger & Run

   To Trigger using the Trigger button on the RF Signal Generator:

   • Set Trigger Source to Trigger Key

   • Set Continuous to Trigger & Run

4. These settings will be applied when you download the IQ waveform and envelope data. Notice that the On-the-Fly indicator in the lower-left corner is set to "Idle." After downloading, the indicator changes to "Connected," allowing you to make real-time changes to these instrument settings.

Step 6: Adjust AWG Output Settings

1. Click the DUT block.

2. Specify how Vpp and Common Mode Offset voltage (Vcm) corresponds to Shaping Table Y-axis.

   Mapped High/Low is mapped to the max value of shaping table Y-axis.

   Vcm sets common mode voltage.

   As you change RF power, actual voltage swing level will be changed (requires re-generation of envelope).

3. Actual AWG voltage setting is shown as “Amplitude” and “Offset” in “Envelope Signal Generator.”

See ETPS Input Voltage Mapping for more information.

Step 7: Generate Signals and Adjust Timing

1. Press “Generate and Download” button in the toolbar to download IQ and envelope data along with initial configurations.

   Notice “Connected” shown in lower left.

2. Perform timing tuning between IQ and envelope.

   Change delay amount and step size.

   Timing adjustment setting is applied as you change the value.