Power Amplifier Test Examples

Introduction

The WCDMA3G_PA_Test_prj provides signal sources compliant with 3GPP technical specification of December 2000. The 3GPPFDD_Synch model is used to ensure all measurements start at the beginning of a slot.

This project focuses on verification of power amplifier designs for 3GPP wireless handsets. Nine measurements are provided including maximum output power, occupied bandwidth, complementary cumulative distribution function (CCDF), spectrum emission, adjacent channel leakage power ratio (ACLR), ACLR in the presence of switching transients, error vector magnitude (EVM), peak code domain error, and code domain power.

Designs for these measurements are described in the following sections; these include:

• Maximum output power measurements: WCDMA3G_PA_UE_OutputPower.dsn
• Occupied bandwidth measurements: WCDMA3G_PA_UE_OccupiedBW.dsn
• CCDF and peak-to-mean information measurements: WCDMA3G_PA_UE_CCDF.dsn
• Spectrum emission measurements: WCDMA3G_PA_UE_SpecEmissions.dsn
• ACLR measurements: WCDMA3G_PA_UE_ACLR.dsn
• ACLR measurements in the presence of switching transients: WCDMA3G_PA_UE_ACLR_SwitchingTransient.dsn
• EVM measurements: WCDMA3G_PA_UE_EVM.dsn
• Peak code domain error measurements: WCDMA3G_PA_UE_PkCodeError.dsn
• Signal power distribution measurements in the code domain: WCDMA3G_PA_UE_CodeDomainPower.dsn

Common variables used in these designs are described in the following table.

VAR Parameters

The following figure shows the top-level schematic for a typical power amplifier test design example.

Power Amplifier Test Design Example Top-Level Schematic

This typical design example and each power amplifier design example include these items.

• The _Info module contains measurement information and specifications.
• The DF (data flow) controller and VAR Simulation_Variables define system simulation parameters.
• The VAR User_Defined_Variables defines parameters for a specific measurement. Designers can customize these settings. Typical parameters settings are:
  • SignalPower = dbmtow(24-DUT_Gain)
  • RF_Freq = 1950 MHz
  • NumSlotsMeasured = 1
• The SUB_3GPP_Source subnetwork (schematic is shown in the following figure) generates the standard reference signal and the real modulated timed signal to be tested. Reference signals are required in some measurements to calibrate the signals to be tested.
  • The measurement channel rate is 12.2 kbps.
  • The spreading factor for DPCCH is 256 and DPDCH is 64.

SUB_3GPP_Source Schematic

• The Device_To_Be_Tested module can be replaced by the designer's power amplifier circuit. A GainRF item with Gain = 1 is used in each example design.
• The _Measure module selects the signal and performs different measurements.

If the RF signal delay (RF_Delay) through the device under test is greater than one chip (0.26 µsec), that delay value can be entered in the _Measure module.

Each design example has a corresponding data display template identified with the corresponding filename with a .dds extension. Power amplifier designers can use the .dds data to display simulation results of their own design. When simulation is complete, a pass or fail message is generated that indicates if results meet specifications. A reference dataset of simulation results of each example design can be found with a prefix of Ref.

Maximum Output Power Measurements

WCDMA3G_PA_UE_OutputPower.dsn Design

Description

This design measures the maximum power of the output signals.

The top-level schematic for this design is shown in the following figure. SUB_3GPP_OutputPower_Info contains measurement information and specifications. The SUB_3GPP_Source subnetwork generates the RF band signal and passes it to the device under test.

WCDMA3G_PA_UE_OutputPower.dsn Schematic

The SUB_3GPP_OutputPower_Measure subnetwork, the following figure, implements the maximum output power measurement based on specifications.

SUB_OutputPower_Measure.dsn Schematic

Simulation Results

Simulation results are shown in the following figure.

In the Data Display window, Page > Equations contains variable definitions and calculations.

WCDMA3G_PA_UE_OutputPower.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation Time: approximately 1 minute

Occupied Bandwidth Measurements

WCDMA3G_PA_UE_OccupiedBW.dsn Design

Description

Occupied bandwidth is a measure of the bandwidth containing 99% of the total integrated power of the transmitted spectrum, centered on the assigned channel frequency. The occupied channel bandwidth must be less than 5 MHz based on a chip rate of 3.84 Mcps.

The top-level schematic for this design is shown in the following figure. SUB_3GPP_OccupiedBW_Info contains measurement information and specifications. The SUB_3GPP_Source subnetwork generates the RF band signal and passes it to the device under test.

WCDMA3G_PA_UE_OccupiedBW.dsn Schematic

The SUB_3GPP_OccupiedBW_Measure subnetwork shown in the following figure implements the occupied bandwidth measurement according to specifications.

SUB_3GPP_OccupiedBW_Measure Schematic

Simulation Results

Simulation results are shown in the following figure. This includes the spectrum with m1 and m2 markers positioned so the lower and higher power ratios equal 0.5%.

In the Data Display window, Page > Equations contains variable definitions and calculations.

WCDMA3G_PA_UE_OccupiedBW.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation Time: approximately 1 minute

Complementary Cumulative Distribution Function Measurements

WCDMA3G_PA_UE_CCDF.dsn Design

Description

Complementary cumulative distribution function (CCDF) fully characterizes the power statistics of a signal. It provides PAR versus probability.

The top-level schematic for this design is shown in the following figure. SUB_3GPP_PA_CCDF_Info contains measurement information and specifications. The SUB_3GPP_Source subnetwork generates the RF band signal and passes it to the device under test.

WCDMA3G_PA_UE_CCDF.dsn Schematic

The SUB_3GPP_PA_CCDF_Measure subnetwork shown in the following figure implements the CCDF measurement.

SUB_3GPP_PA_CCDF_Measure Schematic

Simulation Results

Simulation results in the following figure show the CCDF curve.

In the Data Display window, Page > Equations contains variable definitions and calculations.

WCDMA3G_PA_UE_CCDF.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation Time: approximately 1 minute

Spectrum Emission Measurements

WCDMA3G_PA_UE_SpecEmissions.dsn Design

Description

This example is used to measure the out-of-band emission of user equipment against the spectrum emission mask.

Out-of-band emissions are unwanted emissions immediately outside the nominal channel resulting from the modulation process and non-linearity in the transmitter but excluding spurious emissions. Spectrum emission mask is a limit to the out-of-band emission.

The spectrum emission mask of the user equipment applies to frequencies 2.5 MHz to 12.5 MHz away from the user equipment center carrier frequency. The out-of-channel emission is specified relative to the user equipment output power measured in a 3.84 MHz bandwidth.

The top-level schematic for this design is shown in the following figure. The SUB_3GPP_SpecEmissions_Measure subnetwork contains measurement information and specifications. The RF modulated signal is generated by the SUB_3GPP_Source and passed to the device under test.

WCDMA3G_PA_UE_SpecEmissions.dsn Schematic

In the SUB_3GPP_SpecEmissions_Measure subnetwork, the following figure, output power is measured with a bandpass root raised-cosine (RRC) filter with a 3.84 MHz bandwidth. The out-of-channel emission is measured by sweeping the center frequency of another bandpass RRC filter.

The designer typically sets parameters for SignalPower, RF_Freq and NumSlotsMeasured on the schematic. If the RF signal delay (RF_Delay) through the device under test is greater than one chip (0.26 µsec), that delay value can be entered in SUB_3GPP_SpecEmissions_Measure.

SUB_3GPP_SpecEmissions_Measure Schematic

Simulation Results

Simulation results are shown in the following figure; this shows the spectrum emission against the emission mask.

WCDMA3G_PA_UE_SpecEmissions.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Data Points: 1 slot for each measurement
• Simulation Time: approximately 30 seconds for 1 point. The overall time depends on the out-of-band frequency bandwidth to be measured.

Adjacent Channel Leakage Power Ratio Measurements

WCDMA3G_PA_UE_ACLR.dsn Design

Description

Adjacent channel leakage power ratio (ACLR) is the ratio of the transmitted power to the power measured in an adjacent channel. Better ACLR can be obtained using a longer filter length for the RRC filter in the signal source. The parameter FilterLength has a default value of 16; however, increasing this value to 24 or 32 should result in a better ACLR. This may also correlate better to ACLR measurements when using instruments from Agilent Technologies. Both the transmitted power and the adjacent channel power are measured with a filter that has a root raised-cosine (RRC) filter response with rolloff of α = 0.22 and a bandwidth equal to the chip rate.

The main source of adjacent channel leakage (ACL) is non-linear effects in the power amplifiers. It directly affects the co-existing performance of systems on adjacent channels. Power leakage is a general noise pollution and degrades performance of the system in the adjacent channel. The standard current values for user equipment are 33 dB or -50 dBm (whichever represents a lower leakage power) at 5 MHz offset, and 43 dB or -50 dBm (whichever represents a lower leakage power) at 10 MHz offset.

The top-level schematic for this design is shown in the following figure. SUB_3GPP_ACLR_Info contains measurement information and specifications. The SUB_3GPP_Source subnetwork generates the RF band signal and passes it to the device under test.

WCDMA3G_PA_UE_ACLR.dsn Schematic

The SUB_3GPP_ACLR_Measure subnetwork (SUB_3GPP_ACLR_Measure Schematic figure) implements ACLR measurements according to specifications. The ACLR_Filter_Bank.dsn subnetwork (ACLR_Filter_Bank Schematic figure) contains filters for ACLR measurement.

SUB_3GPP_ACLR_Measure Schematic

ACLR_Filter_Bank Schematic

Simulation Results

Simulation results in the following figure show main and adjacent channel spectrums.

In the Data Display window, Page > Equations contains variable definitions and calculations.

WCDMA3G_PA_UE_ACLR.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation Time: approximately 1 minute

Adjacent Channel Leakage Power Ratio Measurements in Presence of Switching Transients

WCDMA3G_PA_UE_ACLR_SwitchingTransient.dsn Design

Description

This design example is used to measure the adjacent channel leakage power ratio (ACLR) in the presence of the switching transient.

ACLR is a measure of transmitter performance. It is defined as the ratio of the transmitted power to the power measured in an adjacent channel. Better ACLR can be obtained using a longer filter length for the RRC filter in the signal source. The parameter FilterLength has a default value of 16; however, increasing this value to 24 or 32 should result in a better ACLR. This may also correlate better to ACLR measurements when using instruments from Agilent Technologies. Both the transmitted power and the adjacent channel power are measured with a filter that has a root raised-cosine (RRC) filter response with rolloff of 0.22 and a bandwidth equal to the chip rate. 3GPP specifications define the minimum requirements for the ACLR.

The top-level schematic for this design is shown in the following figure. The RF modulated signal, generated by the SUB_3GPP_Source subnetwork, is passed to the device under test.

WCDMA3G_PA_UE_ACLR_SwitchingTransient.dsn Schematic

The SUB_3GPP_ACLR_SwitchingTransient_Measure subnetwork, the following figure, measures the power of four adjacent channels as well as the user equipment channel power. The ACLR is measured through four measurement intervals (time slots) to present the switching transients.

The designer typically sets parameters for SignalPower, RF_Freq and NumSlotsMeasured on the schematic. If the RF signal delay (RF_Delay) through the device under test is greater than one chip (0.26 µsec), that delay value can be entered in the SUB_ACLR_SwitchingTransient_Measure subnetwork.

SUB_ACLR_SwitchingTransient_Measure Schematic

Simulation Results

Simulation results (WCDMA3G_PA_UE_ACLR_SwitchingTransient.dds) are shown in the following figure. The specification requires that if adjacent channel power is greater than -50dBm then the ACLR must be higher than the value specified in the following table.

ACLR Measurement Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Data Points: 1 slot for each measurement
• Simulation Time: approximately 2 minutes

Error Vector Magnitude Measurements

WCDMA3G_PA_UE_EVM.dsn Design

Description

Error vector magnitude (EVM) is a measure of the difference between the measured waveform and the theoretical modulated waveform (the error vector). It is the square root of the ratio of the mean error vector power to the mean reference signal power expressed as a percentage. The measurement interval is one power control group (time slot).

The top-level schematic for this design is shown in the following figure. SUB_3GPP_PA_EVM_Info contains measurement information and specifications. The SUB_3GPP_Source subnetwork generates the RF band signal and passes it to the device under test.

WCDMA3G_PA_UE_EVM.dsn Schematic

The SUB_3GPP_PA_EVM_Measure subnetwork, the following figure, implements the error vector magnitude measurement.

SUB_PA_EVM_Measure Schematic

Simulation Results

Simulation results are shown in the following figure.

In the Data Display window, Page > Equations contains variable definitions and calculations.

WCDMA3G_PA_UE_EVM.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation Time: approximately 1 minute

Peak Code Domain Error Measurements

WCDMA3G_PA_UE_PkCodeError.dsn Design

Description

This example is used to measure the peak code domain error of user equipment transmitted signal.
The top-level schematic for this design is shown in the following figure. A channel mixed signal is generated by SUB_3GPP_Source subnetwork, then passed to the device under test.

WCDMA3G_PA_UE_PkCodeError.dsn Schematic

The SUB_3GPP_PA_PkCodeError_Measure subnetwork, the following figure, implements the peak code domain error measurement. The tested signal and the reference signal are measured with filters that have root raised-cosine filter response with rolloff of 0.22 and a bandwidth equal to the chip rate.

SUB_3GPP_PA_PkCodeError_Measure Schematic

The peak code domain error is calculated by projecting the error vector power on each code channel in a spreading code set. Code layer can be used to define the code set. If code layer is n, then the spreading factor for the code set is 2ⁿ. In this example, the spreading factor is 4, so code layer is set to 2. The code domain error of each code is defined as the ratio of the mean power of the projection onto that code to the mean power of the composite reference waveform. This ratio is expressed in dB. The peak code domain error is defined as the maximum value for the code domain error for all codes. As in FDD/uplink each code can be used twice on the I channel or on the Q channel. Code domain error must be measured on both channels. The measurement interval is one power control group (time slot).

Simulation Results

Simulation results are shown in the following figure. This shows the code domain error of the tested signal on the I and Q channels; peak code domain error occurs on the Q channel.

• I channel peak code domain error = −106.883 dB
• Q channel peak code domain error = −107.059 dB
• Overall peak code domain error = −103.960 dB
  

WCDMA3G_PA_UE_PkCodeError.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Data Points: 1slot per code (2560 chips per slot)
• Simulation Time: approximately 1 minute

Signal Power Distribution Measurements in Code Domain

WCDMA3G_PA_UE_CodeDomainPower.dsn Design

Description

This example is used to measure signal power distribution across the set of code channels, normalized to the total signal power.

The top-level schematic for this design is shown in the following figure. The RF modulated signal generated by the SUB_3GPP_Source subnetwork is passed to the device under test.

WCDMA3G_PA_UE_CodeDomainPower.dsn Schematic

The SUB_3GPP_PA_CodeDomainPower_Measure subnetwork, the following figure, implements the code domain power measurement.

SUB_3GPP_PA_CodeDomainPower_Measure Schematic

Code domain power is measured with a filter that has a root raised-cosine filter response with a rolloff of 0.22 and a bandwidth equal to the chip rate.

Code domain power is measured at the C(8) layer, that is the signal is decoded by the OVSF codes of SF = 256. This is legitimate because the power attributable to a traffic channel using a higher rate spreading code will correlate with the block of K adjacent codes at the level for which the higher rate code is the parent. (K is the ratio between the used spreading factor and 256.) Provided that all the codes in this block are identified as used codes then the aggregate power of the K codes in the block will equal the signal power of the higher rate code.

The designer typically sets parameters for SignalPower, RF_Freq and NumSlotsMeasured on the schematic. The measurement interval is one power control group (time slot).

Simulation Results

The vector of code domain power is plotted as a histogram to display the power distribution in the code domain. Simulation results in the following figure show the power distribution of the transmitted signal.

Since it is an ideal design, levels for the inactive channels are zero; in reality, signal and system imperfections compromise the code orthogonality and result in a certain amount of signal power projecting onto inactive codes. A real signal will also have a certain noise level that, being random, will project more or less evenly onto all codes.

WCDMA3G_PA_UE_CodeDomainPower.dds Simulation Results

Benchmark

• Hardware Platform: Pentium III 450 MHz, 512 MB memory
• Software Platform: Windows NT 4.0 Workstation, ADS 2002
• Data Points: 1 slot per code (2560 chips per slot)
• Simulation Time: approximately 1 minute

References

1. 3GPP Technical Specification TS 25.101 V3.5.0 "UE: Radio transmission and Reception (FDD)," December 2000.
2. 3GPP Technical Specification TS 34.121 V3.3.0 "Radio transmission and reception (FDD)," December 2000.