Making Pulse Power Measurements With Maury ATS 4.00

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1 MAURY MICROWAVE CORPORATION 8 November 2004 Making Pulse Power Measurements With Maury ATS 4.00 Author: John Sevic, MSEE; Automated Tuner System Technical Manager, Maury Microwave Corporation Abstract: Maury ATS version 4.00 now offers advanced pulse power measurement capability for modern wireless standards such as GSM, EDGE, and GSM/EDGE/GPRS, and for common pulse applications, such as RADAR. With direct configuration of pulse-capable power meters from ATS and dedicated calibration/measurement functions for pulse measurements, making pulse measurements and analyzing DUT pulse performance characteristics is as simple as performing CW measurements. In addition to pulse average power, pulse peak power, peak-average ratio, and peakminimum ratio can also be analyzed. Time-gated measurements are supported, to analyze GPRS or multi-slot basestation signals. The present Application Note provides an overview of the new features, ATS configuration and calibration with pulse measurements, and performing pulse measurements and data analysis. Why Make Pulse Power Measurements? Pulse power measurements are necessary in many loadpull characterization applications based on TDMA or pulsed power, such as GSM/EDGE, Bluetooth, and RADAR. Time-gated pulse power measurements find application in characterization of arbitrary pulses embedded within a stream of pulses, such as with GSM/EDGE/GPRS. Pulse power measurements also find application in isothermal model extraction and validation. Traditionally, pulse power measurements were made using electrothermal-based power meters. To calculate the approximate instantaneous power of the pulse, an electrothermal-based meter applies simple linear scaling of the duty-ratio to the measured power. For example, if the pulse width is 10% of the period, and the power meter reads 1 W, then the instantaneous power is 10 W 1. Instantaneous power is often used interchangeably with peak envelope power, or PEP. Our definition treats the power measured in this fashion as pulse average power. Therefore, in this example, pulse average power is 10 W. Diode-based peak power meters overcome all of the limitations of electrothermal-based power meters while adding additional capabilities, such as timegating. Specially designed diode-based peak power meters can track the instantaneous RF envelope, to further enable signal analysis, such as calculation of average power over an arbitrary time span, calculation of peak-average ratio, or calculation of peak-mean ratio. With time-gating, diode-based peak power meters can also isolate specific pulses out of many to capture the characteristics of that pulse only. In summary, pulse power measurements with Maury ATS are useful for Peak and average power measurement of short pulses with a difficult-to-define duty-ratio, due to the transient response of the bias network, which can occur with pulsed RADAR. Peak and average power measurement of specific pulses out of several, occurring with GPRS, for example. Measurement of signal quality metrics such as peak-average ratio and peak-minimum ratio for contemporary wireless standards like GSM, EDGE, NADC, and GSM/EDGE/GPRS. 1 Note that this definition is not, strictly speaking, true. The power that is returned is still the average power, specifically pulse average power. We include the nomenclature instantaneous power to remain consistent with the, somewhat erroneous, classical use of instantaneous, or peak envelope power, as found in RADAR applications. In this sense, an electro-thermal power sensor is incapable of true instantaneous power measurements, though, classically, the industry has assumed it is, nevertheless, instantaneous, or peak, power. In the present Application Note, we adopt pulse average power for this quantity. Copyright 2003 Maury Microwave Inc., all rights reserved. technical data 5C-059 Page 1 of 6

2 8 November 2004 Pulse Power Measurement Capabilities of Maury ATS ATS enables direct configuration of supported power meters for pulse power measurements. Measurements are made asynchronously and assume the signal source has been properly configured to generate the appropriate modulation or pulse format. Refer to Table 1 below for supported power meters. Two modes are supported for pulse measurements. The first mode uses a conventional electrothermalbased power meter and assumes that the duty-ratio is known and well-defined. Only pulse average power is returned in this mode. The second mode uses a diode-based peak power meter, thus enabling peak power measurements of an arbitrary nature, independent of knowing or defining a duty-ratio; statistical signal analysis is also supported in this mode. Depending on the meter and sensor chosen, measurement of pulse widths on the order of 1 µs are possible. Pulse average power, pulse peak power, peak-average ratio, and peakminimum ratio are returned, and are treated as a standard measurement variable within ATS (e.g. they may be plotted on a Smith chart). Preconfigured instrument states are available for GSM/EDGE, Bluetooth, and 10 µs pulse 1% duty-ratio RADAR. Custom configuration is also possible, to look at, for example, an arbitrary slot within a GPRS frame. Synchronous pulse bias is not (currently) supported, nor are instantaneous power measurements made with a VSA. Therefore, while isothermal measurements can be made, preamble-triggered measurements cannot. Presently, pulse power measurements are done asynchronously, with DC bias applied, RF applied, followed by the power measurement. The RF source must be properly configured prior to making measurements. Configuring ATS For Pulse Power Measurements Configuring ATS for pulse power measurements is similar to standard CW power configuration. The only differences are that the RF signal source must be configured to generate the desired signal and ATS must be configured to correctly set up the power meter to capture the pulse. Two options are available for measuring pulse power: electrothermal-based sensor mode and diode-based sensor mode. If the electrothermal-based mode is selected, then pulse average power of the pulse stream is returned (see foot-note #1 above regarding the definition of pulse average power when using an electrothermal-based sensor). If the diode-based sensor mode is selected, pulse average power, pulse peak power, peak-average ratio, and peak-minimum ratio are returned; these variables are handled as conventional ATS measurement variables. The Agilent E4416A/E4417A series power meters and Boonton 4300/4400/4500 series power meters each support peak power measurements using diode-based peak power sensors, while the Agilent 436/437/438 series power meters support average power measurements only, using electrothermal- or diode-based sensors. Note that special considerations must be given to use of electrothermal-based power sensors. Simple power scaling is done by using the duty-ratio specified in ATS. Since pulse uniformity is assumed, this option can only be used when the transient response of the DUT, its bias network, and its thermal network can be ignored with respect to a well-defined duty-ratio. For example, power measurement of pulses on the order of 10 µs with electrothermal-based power sensors can lead to errors if the transient portion of the pulse is an appreciable portion of the pulse duration, which is often the case. Peak power pulse measurements can be made only with peak-capable diode-based sensors. ATS provides direct software control of such power meters to enable analysis of arbitrary pulses, as well as providing preconfigured settings for single-slot GSM/EDGE (captures slot 0), Bluetooth, and 10 µs pulse 1% dutyratio RADAR. The no uniform pulse option is also useful in those applications where transient responses cannot be ignored or certain slots out of a frame need to be isolated to measure only their power. To configure ATS for pulse power characterization, first ensure that the appropriate Maury-supplied instrument drivers have been selected, from the <Instruments> options, for both the RF signal source and the power meter. Configure the RF signal source to create the signal desired (follow the instructions provided with the RF signal source). Table 1 below shows the driver name associated with each supported power meter, along with the type of supported measurements and the measurement parameters that are returned for display in ATS. 5C-059 technical data Page 2 of 6

3 MAURY MICROWAVE CORPORATION Next, configure the power meter by going to <Options>, <Options & Configuration>, and <Pulse>. The control panel shown in Figure 1 appears. To measure pulse power using an electrothermalbased sensor, click the Electrothermal-Based Power Sensor radio button, which will activate its associated parameter entry boxes. Enter the duty-ratio of the pulse that will be measured, in %. Leave the Pulse Period entry empty; its presence is for support of legacy user functions and certain obsolete drivers, and has no effect on pulse power measurement. 9 September 2004 There are several options to measure peak pulse power using a diode-based power sensor; this option is also used to isolate particular slots out of a frame to analyze the power of the desired slot. Note also from Figure 1 that the signal source state can be recalled too. This is useful to recall the state that is appropriate for the type of pulse measurement being done. Table 1: Supported Power Meters, Sensors, and Power Supplies for Pulse Measurements with Maury ATS. Copyright 2003 Maury Microwave Inc., all rights reserved. technical data 5C-059 Page 3 of 6

4 Figure 1: Pulse Power Options Dialog. Figure 2: Timing Definitions for Preconfigured Measurements 5C-059 technical data Page 4 of 6

5 MAURY MICROWAVE CORPORATION GSM/EDGE, NADC, iden, and RADAR. Click on the Diode-Based Power Sensor radio button and next click on the Preconfigured Pulse Measurements radio button to select a preconfigured measurement. For GSM/EDGE, the preconfigured option assumes the first slot of a frame is active, denoted as slot 0. The Bluetooth option assumes a DH1 data burst. The RADAR option assumes a 10 µs pulse width with a 1% duty-ratio. Each of the preconfigured options triggers uses the Auto-Trigger setting of the power meter. Figures 2 illustrates the definitions of each of the measurement parameters to capture a pulse. Table 2 shows the associated parameters for each preconfiguration. Note that the RF signal source must be configured to match the parameters shown in Figure 2. The preconfigured options are set to ignore the ramp-up and ramp-down sections of the pulse, with integration time-spans based on the respective wireless standards; this is often referred to as the useful part of the burst. The RADAR preconfiguration captures the entire 10 µs pulse. Number of Averages is how many periods of the signal are captured before returning a measurement to ATS. Inserting a 0 in the Averages field will set the averaging to Auto mode, which works well for most applications. Inserting a 0 in the Trigger Level field will set the Trigger to Auto mode, which works well for most applications. The Trigger Level, if specified, will be with respect to the mean power of the pulse, in dbc. This simplifies deembedding the trigger level back to the DUT reference-plane to what is displayed on the power meter, since the trigger level is now independent of the loss between the DUT reference-plane and the power sensor reference-plane. To perform a pulse power measurement using a custom configuration, click on the Diode-Based Power Sensor radio button and next click on the User-Specified Pulse Measurements radio button. This will activate the parameter boxes in the Custom Pulse Setup of the Pulse Power Setup dialog shown in Figure 1. From here, enter the parameters necessary to capture the pulse. Note that these parameters can be set to measure arbitrary pulses, within the capability of the associated power sensor. Measurement of specific slots within a frame, for wireless standards, is also possible by using Trigger Delay and Trigger Hold-off to isolate the slot of interest. Refer to the Users Manual for the appropriate power meter for specific details. To perform a completely custom pulse power measurement, outside of the flexibility provided from within ATS, click the Recall Power Meter State radio button and enter the power-meter state to be recalled. Using this option enables custom power meter configuration directly with the power meter. In addition, through the use of ATS User-Functions, additional data can be returned to ATS from the power meter. For example, one could return power droop or power of certain slots within a frame. Table 2: Preconfigured Measurement Settings for GSM/EDGE, Bluetooth, and RADAR Copyright 2003 Maury Microwave Inc., all rights reserved. technical data 5C-059 Page 5 of 6

6 Calibrating ATS for Pulse Power Measurements To calibrate for Pulse Power, select <Calibrate> from the SNPW menu, and then select <Pulse/GSM/EDGE>. Choose either <New Cal> or <Get Cal File> to begin a new calibration or to load a previous calibration, respectively. The calibration sequence from this point on is identical to the standard CW power calibration procedure in Section 5.4 of the ATS Users manual. Note that prior to calibration, the measurement configuration must be completed, as described above. Also, all pulse calibration files have a.pcl extension. Performing Pulse Power Measurements with ATS To calibrate for Pulse Power, select <Calibrate> from the SNPW menu, and then select <Pulse/GSM/EDGE>. Choose either <New Cal> or <Get Cal File> to begin a new calibration or to load a previous calibration, respectively. Alternatively, use <Shift+Ctrl+M> or <Ctrl+M> hotkeys, respectively. The calibration sequence from this point on is identical to the standard CW power calibration procedure in Section 5.4 of the ATS Users manual. Note that prior to calibration, the measurement configuration must be completed, as described above. Pulse Power Characterization with ATS Analysis and plotting of loadpull data with pulse measurements is identical to standard loadpull, with the addition of the new variables specified in Table 1. When an electrothermal-based power meter is used, all power-dependent variables within the Measurement Parameter list, e.g. Pout, Gt, and PAE, are referred to pulse average power. For example, if the pulse width is 10% of the period, and the power meter reads 1 W, then the pulse average power is 10 W 2, and all measurements will be referred to this power. Note that DC current measurements are also referred to using the duty-ratio factor specified in the Pulse Options Dialog of Figure 1. Similarly, when a diode-based power meter is used, all power-dependent variables within the Measurement Parameter list, e.g. Pout, Gt, and PAE, are referred to pulse average power. However, in this case, the pulse average power is based on integrating the peak power over the specified time-span, resulting in improved accuracy in the event of transients. This mode also returns three additional variables: pulse peak power, peak-average ratio, and peak-minimum ratio. The peak, average, and minimum power values are taken only within the specified time-span. Measurement of pulse DC current requires use of specialized equipment, such as a pulse-capable power supply or an oscilloscope with a Hall-effect sensor. Currently, ATS 4.00 supports the Agilent line of 663xx series of pulse-capable power supplies only. 2 See Footnote #1 for clarification of definitions of pulse average power. 5C-059 technical data Page 6 of 6