Phase and Amplitude versus Time Measurement Description

How is a Phase and Amplitude versus Time Measurement Made?

The Phase and Amplitude versus Time measurement provides a way to characterize the magnitude and phase errors introduced by the non-linear effects of power amplifiers operating over a wide dynamic range. Measuring the amplitude, phase and frequency as a function of output level makes it possible to create a more accurate output signal by pre-distorting the input signal to the power amplifier.

The Phase and Amplitude versus Time measurement is performed on a continuous wave signal with either a discrete amplitude step waveform (Discrete Waveform Calibration Signal) or continuous ramp waveform (Continuous Waveform Calibration Signal). This measurement requires you to put your mobile station into a test mode that can command the mobile station to generate a waveform, which can be either discrete or continuous.

The Discrete Waveform Calibration Signal may include up to 512 measurement intervals (steps), which can be of varying widths (100 us to 400 ms) and amplitudes (-20 dBm to +35 dBm). For this waveform, you can configure the test set to return different types of results, these are: power, phase, and frequency results ( PCAL ), amplitude and phase pairs ( SAMPle ), or both ( BOTH ). The test set samples the discrete waveform at an effective rate of 156.25 kHz. The results returned by the test set depend on the Result Type parameter setting.

The Continuous Waveform Calibration Signal can be classified as three different waveform types: CONTinuous, CONT2 and CONT3. When the Waveform Type is CONTinuous, the signal required by the test set is a 577us GMSK initial reference burst, followed by a CW signal. The initial reference burst is used to range the expected input power and can be used to trigger the Phase and Amplitude versus Time measurement. The CONT2/CONT3 waveform measures a modulated burst signal (and does not require an initial reference burst). The differences in the way the test set performs measurements on these three waveform types are the effective sampling rate at which the test set returns results and the measurement sample count. For the CONTinuous waveform types, the sampling rate is 1.083 MHz and the maximum count is 5000; for the CONT2 waveform types the sampling rate is 4.333 MHz and the maximum count is 5000; for the CONT3 waveform types the sampling rate is 10 MHz and the maximum count is 50000. The results returned by the test set are amplitude and phase pairs.

This measurement can be armed as a single measurement only. Once triggered, the test set performs a measurement on the mobile generated waveform. The type of measurement and the format of the measurement results depend on the type of waveform (DISCrete, CONTinuous, CONT2, or CONT3) your mobile station generates and, for the DISCrete waveform, the Result Type parameter setting.

Before starting the Phase and Amplitude versus Time measurement, you should first specify the mobile station's Measurement Frequency and the Expected Power Control on the test set. The Expected Power Level should be set to the maximum power level in the mobile generated waveform, and the RF Generator's cell power should be set to OFF . Also before starting, you should specify any waveform specific parameters. See Configuring a Discrete Waveform Calibration Signal and Configuring a Continuous Waveform Calibration Signal .

The accuracy of this measurement relies heavily on the Spectrum Monitor calibration.

Phase and Amplitude versus Time Measurement Parameters

• Filter Type

  This parameter allows you to select the bandwidth filter used for the measurement. The test set provides three types of filter: WIDE, NARRow and ENARrow. You can select the filter type according to the following table. For example, if you want to measure the Power results of a signal with interference out of band, and do not concern much on the test speed, you can select Filter Type ENARrow .

  	Anti-interference ability	Test Speed	Returned Results
  WIDE	Weak	Fast	Power, phase and frequency
  NARRow	Strong	Slow(*)	Power, phase and frequency
  ENARrow	Strong	Slow(*)	Only Power results are valid. The phase and frequency results are always Nan.
  *When the Filter Type is set to NARRow or ENARrow, the Interval Widths is recommended to be larger than 1ms, which will influence the test speed.

  The GPIB command to set this parameter is SETup:PCALibration:FILTer .

• Interval Count

  This parameter is only applicable when the Waveform Type is DISCrete . This is the total number of steps the test set is to measure.

  You must make sure the Interval Count, the number of Interval Centers , and the number of Interval Widths are consistent. The number of returned results depends on the step count. If the number of Interval Centers and/or Interval Widths is less than the Interval Count, invalid data is returned.

  The GPIB command to set this parameter is SETup:PCALibration:STEP:COUNt .

• Interval Centers

  This parameter is only applicable when the Waveform Type is DISCrete .This is the time location of the center of each step relative to the time when the trigger event occurs.

  The GPIB command to set this parameter is SETup:PCALibration:STEP:CENTer .

• Interval Widths

  This parameter is only applicable when the Waveform Type is DISCrete .This is the stable portion, or portion you wish to measure, of each power step.

  The GPIB command to set this parameter is SETup:PCALibration:STEP:WIDth .

• Measurement Sample Count

  This parameter is only applicable when the Waveform Type is CONTinuous , CONT2, or CONT3 . This parameter sets the total number of amplitude and phase samples to be reported by the test set in the Phase and Amplitude versus Time measurement results.

  The range of the sample count is:

  • 1 to 5000 when the Waveform Type is set to CONTinuous or CONT2;
  • 1 to 50000 when the Waveform Type is set to CONT3 .

  If you change a CONT3 Measurement to CONTinuous or CONT2 , the count value will be automatically set to 1 if it is originately over 5000. A warning message is popped up to notify the change.

  The GPIB command to set this parameter is SETup:PCALibration:MEASurement:COUNt .

• Measurement Delay

  This parameter is only applicable when the Waveform Type is CONTinuous . This parameter is the time the test set waits after the initial reference burst before is starts sampling data to and processing the data into amplitude and phase results.

  The GPIB command to set this parameter is SETup:PCALibration:MEASurement:DELay .

• Result Type

  This parameter only applicable when the Waveform Type is DISCrete . This parameter can be set to one of three options: PCAL , SAMPle , or BOTH . The setting for this parameter determines what type of measurement results the test set returns after measuring the Discrete Waveform Calibration Signal. For information on the type of results the test set returns base on the setting of this parameter, see Phase and Amplitude Measurement Results for a Discrete Waveform .

  The GPIB command to set this parameter is SETup:PCALibration:RESult:TYPE .

• Timeout

  You can set the timeout state and time for this measurement. To set them separately, use SETup:PCALibration:TIMeout:STATe to set the timeout state, SETup:PCALibration:TIMeout:TIME to set the timeout time, or SETup:PCALibration:TIMeout:STIMe to set the state and time using the complex command.

• Trigger Delay

  This is the specified time between the trigger event and when the test set begins sampling data.

  The range of the trigger delay is:

  • 0 to 10 ms when the Waveform Type is set to DISCrete or CONTinuous;
  • -2.31001 to 10 ms when the Waveform Type is set to CONT2 or CONT3.

  If you change a CONT2 /CONT3 Measurement to DISCrete or CONTinuous, the trigger delay will be automatically set to zero if it is originately negative. A warning message is popped up to notify the change.

  The GPIB command to set this parameter is SETup:PCALibration:TRIGger:DELay .

• Trigger Source

  You can set the Trigger Source to IMMediate , RISE (RF Rise), or EXTernal . See Triggering of Measurements .

  The GPIB command to set this parameter is SETup:PCALibration:TRIGger:SOURce .

• Trigger Threshold

  This is the level below the maximum power level (the power level of the initial reference burst) at which the measurement triggers. That is, the trigger threshold is the offset below the Expected Input Power plus the RF Amplitude Offset value. This parameter only applies if the Trigger Source is set to RISE.

  The GPIB command to set this parameter is SETup:PCALibration:TRIGger:THReshold .

• Waveform Type

  This parameter classifies the characteristics of the calibration signal generated by the mobile station. The settings available for this parameter are DISCrete, CONTinuous, CONT2, or CONT3. See Configuring a Discrete Waveform Calibration Signal and Configuring a Continuous Waveform Calibration Signal for more information.

  Note, for certain feature licenses the waveform type must be set to CONT2 or CONT3 to initiate the measurement.

  • DISCrete - This setting configures the test set to expect a calibration signal generated by the mobile station that consists of a sequence of finite length power bursts with no burst in the sequence having a higher maximum power level than the first burst, which transitions through the trigger level threshold.
  • CONTinuous -This setting configures the test set to expect a waveform consisting of a GMSK initial power burst (577 µs wide) to trigger the measurement, followed by a continuous waveform.
  • CONT2 - This setting is similar to the CONTinuous setting except that it uses different type of filtering and a different sample rate.
  • CONT3 - This setting is similar to the CONTinuous setting except that it uses different type of filtering and a different sample rate. It supports measureing a wideband signal.

  The GPIB command to set this parameter is SETup:PCALibration:WAVeform:TYPE .

Phase and Amplitude versus Time Measurement Results

The test set returns the Phase and Amplitude versus Time measurement results via the GPIB interface only. The Phase and Amplitude versus Time measurement results depend on the mobile generated waveform type.

If the waveform you are measuring is a discrete waveform, see Phase and Amplitude Measurement Results for a Discrete Waveform .

If the waveform you are measuring is a continuous waveform, see Phase and Amplitude versus Time Measurement Results for a Continuous Waveform .

Phase and Amplitude versus Time Input Signal Requirements

The Phase and Amplitude versus Time measurement has the following input signal requirements:

• Frequency: 292.5 MHz to 2700 MHz
• Input Signal Level: -20 dBm to +35 dBm

Calibrating the Phase and Amplitude versus Time Measurement

This measurement automatically calibrates the phase and amplitude results when the waveform type is DISCrete or CONTinuous. However, to ensure triggering accuracy when the trigger source is set to RF Rise, you must run the Spectrum Monitor Calibration at least once a month.

This measurement is not automatically calibrated when the waveform type is CONT2 or CONT3; it relies on the Spectrum Monitor calibration factors.

See Recommended Calibration Intervals for more information on when the Spectrum Monitor calibration should be performed.

Related Topics

Spectrum Monitor Calibration

Programming a Phase and Amplitude vs. Time Measurement (Discrete Waveform)

Programming a Phase and Amplitude vs. Time Measurement (CONTinuous Waveform)

Programming a Phase and Amplitude vs. Time Measurement (CONT2 Waveform)

SETup:PCALibration

FETCh:PCALibration

Phase and Amplitude versus Time Troubleshooting