# Patent

## Title
Pulsed behavior modeling with steady state average conditions

## Abstract

A method for pulsed behavior modeling of a device under test (DUT) using steady state conditions is disclosed. The method includes providing an automated test system (ATS) programmed to capture at least one behavior of the DUT. The ATS then generates a DUT input power pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level. At least one behavior of the DUT is then captured by the ATS while the input power is at the predetermined pulse level. The ATS then steps the predetermined pulse level to a different predetermined pulse level, and the above steps are repeated until a range of predetermined pulse levels is swept. The ATS then steps the predetermined steady state level to a different steady state level, and the above steps are repeated until a range of predetermined steady state levels is swept.

## Background
RELATED APPLICATIONS
This application claims the benefit of provisional patent application Ser. No. 61/508,187, filed Jul. 15, 2011, the disclosure of which is hereby incorporated herein by reference in its entirety.


FIELD OF THE DISCLOSURE
The present disclosure is related to modeling the behavior of a device under test (DUT). In particular, the present disclosure is related to pulse behavior modeling of DUTs such as power amplifiers (PAs).
BACKGROUND
Behavior models are valuable tools for power amplifier (PA) design and system analysis. As shown in FIG. 1, a traditional approach for obtaining a behavior models for PAs relies on pulsed measurements where an input power sweep is performed at a low duty cycle with a device under test (DUT) turned off during a remaining portion of the duty cycle. The exemplary input power sweep shown in FIG. 1 has a 5% duty cycle with an average input power of −100 dBm, wherein an instantaneous input power (PINST) is stepped from −30 dBm to 10 dBm in 1 dB steps. During the DUT off portion of the duty cycle, the DUT is disabled by removing the average input power or by disabling the bias to the DUT. An average input power of −100 dBm as shown in FIG. 1 effectively disables the DUT for 95% of the duty cycle. However, leaving the DUT off for such a relatively long portion of the duty cycle prevents the DUT from reaching steady state conditions associated with operation of the DUT in various applications. Consequently, data collected using the traditional approach will result in relatively inaccurate modeling of DUT performance for relatively complex applications that use one or more DUT models to generate pre-distortion for a PA. Thus, there remains a need for a method and system that accurately models DUT performance for operating conditions encountered in complex systems such as an envelope tracking system that employs pre-distortion to linearize an associated PA.
SUMMARY
The present disclosure provides a method for pulsed behavior modeling of a device under test (DUT) using steady state conditions. The method includes providing an automated test system (ATS) programmed to capture at least one behavior of the DUT. The ATS then generates a DUT input power pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level. At least one behavior of the DUT is then captured by the ATS while the input power is at the predetermined pulse level. The ATS then steps the predetermined pulse level to a different predetermined pulse level, and the above steps are repeated until a range of predetermined pulse levels is swept. The ATS then steps the predetermined steady state level to a different steady state level, and the above steps are repeated until a range of predetermined steady state levels is swept.
In at least one exemplary embodiment, the present disclosure also provides for an extended method that adds pulse modeling of PA behavior under envelope tracking conditions. This extended method further includes a step of setting a predetermined average PA supply voltage in association with generating the input power signal for the DUT. The extended method further includes stepping a predetermined PA supply voltage pulse level to a different predetermined PA supply pulse level via the ATS in connection with stepping the predetermined steady state level to a different steady state level. Moreover, a tangible computer-readable medium having instruction code stored thereon is provided for instructing a computing device of the ATS to perform operations for pulsed behavior modeling of the DUT. Further still, in one exemplary embodiment, the tangible computer readable medium may also be writable for recording data related to pulsed behavior of the DUT captured using the present method.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.



BRIEF DESCRIPTION OF THE DRAWING FIGURES
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
FIG. 1 is a graph of input power versus time of an input power sweep used to obtain a traditional device under test (DUT) behavior model.
FIG. 2 is a graph of input power versus time of an input power sweep usable to obtain a DUT behavior model according to the present disclosure.
FIGS. 3A and 3B are graphs of exemplary input power and supply voltage sweeps usable to obtain a DUT behavior model under a steady state average condition.
FIG. 4 is a graph of exemplary amplitude modulation—amplitude modulation (AMAM) data corresponding to a family of steady state average power input curves.
FIG. 5 is graph of exemplary amplitude modulation—phase modulation (AMPM) data corresponding to a family of steady state average power input curves.
FIG. 6 is a graph of exemplary UMTS Terrestrial Radio Access (U TRA) Adjacent Channel Leakage Ratio (ACLR) results produced with a DUT behavior model obtained via the present method for pulsed behavior modeling of a DUT using steady state conditions.
FIG. 7 is a block diagram of an automatic test system (ATS) configured to implement the present method for pulsed behavior modeling of a DUT using steady state conditions.
FIG. 8 is a flow chart of a general method for conducting pulsed behavior modeling with steady state average conditions.
FIG. 9A is a flow chart of an enhanced method for conducting pulsed behavior modeling with steady state average conditions.
FIG. 9B is a continuation of the flow chart of FIG. 9A.



DETAILED DESCRIPTION
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
The present disclosure provides a test process that applies average steady state type operating conditions to a device under test (DUT) during the time between input power pulses that are swept over a range of predetermined input power pulse levels. Average operation conditions could vary based on the type of DUT. For example, in a standard linear PA, the average condition may be achieved by applying average RF power at a RF input of the DUT with nominal bias applied. In another example, an envelope tracking PA might achieve average steady state conditions by applying both the average RF input power and average supply voltage that is typically a collector voltage (VCC) or drain voltage (VDD).
FIG. 2 is a graph of input power versus time of an input power sweep usable to obtain a DUT behavior model according to the present disclosure. In this exemplary case, a pulse measurement is modified to set an average steady state operating condition during the DUT off portions of a duty cycle. This is accomplished by setting an RF input drive level to a desired average power during the off portion of the duty cycle. In an exemplary case depicted in FIG. 2, the RF input drive level is set to 0 dBm average power during the off portion of the duty cycle, which in this case is for 95% of the duty cycle. During the other 5% of the time an instantaneous input power pulse PINST is applied to the input of the DUT. It is to be understood that the term instantaneous is a relative term that is used to describe a relatively sharp transition from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level. In this exemplary case shown in FIG. 2, PINST is swept in an incremental fashion over a range that extends from a beginning predetermined pulse level of −30 dBm to an ending predetermined pulse level of 10 dBm using 1 dB steps. However, other beginning and ending predetermined pulse levels as well as other step sizes may be chosen. Moreover, the predetermined levels for PINST can be decremented from a beginning predetermined to an ending predetermined pulse level instead of incremented, or the order of the predetermined levels for PINST can be randomized.
FIGS. 3A and 3B are graphs of exemplary input power and supply voltage sweeps usable to obtain a DUT behavior model under a steady state average condition. These input power and supply voltage sweeps are particularly useful for modeling the behavior of a DUT used in an envelope tracking system. In this scenario, both a RF input drive level Pin (FIG. 3A) and a supply voltage VCC (FIG. 3B) are set to average operating conditions between steps of a measurement sweep. In this exemplary case, the average Pin is −2.5 dBm and the average VCC is 2.5V. The Pin sweep range is −20 dBm to 10 dBm in 5 dB steps and the VCC sweep range is 1V to 3V in 1V steps. In this exemplary case, the Pin sweep of the predetermined pulse levels is nested inside the VCC sweep of predetermined supply voltage pulse levels (VCCINST).
Application of an average steady state condition for input power can significantly affect the thermally sensitive characteristics of a DUT. As an example, consider the amplitude modulation—amplitude modulation (AMAM) and amplitude modulation—phase modulation (AMPM) measurements of a typical PA. FIG. 4 is a graph of AMAM measurements, while FIG. 5 is a graph of AMPM measurements. Taken together, the family of curves in both graphs shows how the complex gain of the typical amplifier varies as the steady state average input power changes during the DUT off portions of the duty cycle.
FIG. 6 is a graph of exemplary results produced with a DUT behavior model obtained via the present method for pulsed behavior modeling of a DUT using steady state conditions. In particular, the graph of FIG. 6 shows the benefit of modeling the behavior of the DUT under steady state average conditions. The behavior model in this exemplary case is UMTS Terrestrial Radio Access (UTRA) Adjacent Channel Leakage Ratio (ACLR) versus output power of the DUT. The dotted and dashed curve reflects a behavior model obtained using the method of the present disclosure where an average operating condition is set at a steady state value by applying an average input power to the DUT during off portions of each duty cycle during a measurement sweep. This behavior model is a compilation of a plurality of average input power drive levels. The dotted and dashed curve was generated from a simulation using this behavior model as a function of average input power. Notice that the dotted and dashed curve shows an improved correlation with lab measurements depicted by the solid curve as compared to the dashed curve generated using a traditional behavior model obtained from sweep measurements taken with the DUT disabled during the off portions of each duty cycle.
FIG. 7 is a block diagram of an automated test system (ATS) 10 that is usable to perform the measurements needed to capture at least one behavior of a DUT 12. The ATS 10 includes a system controller 14 that has a computing device that executes code from a tangible computer-readable medium 16. The system controller 14 provides test signals to the DUT 12. These test signals can include but are not limited to, input power levels, bias levels, and supply voltage levels. The DUT 12 provides at least one output in response to such test signals. The output of DUT 12 is detected by a behavior sensor 18 that captures at least one behavior via at least one measurement that is transmitted to the system controller 14. The behavior sensor 18 can be, but is not limited to, a power detector, a voltmeter, and a phase detector. Data for a behavior model for the DUT 12 can then be recorded to the tangible computer-readable medium 16. The system controller 14 may derive the behavior model for the DUT 12 using the data of the captured behavior or the system controller 14 can pass along the data of the captured behavior to an external processor (not shown) for behavior model generation.
FIG. 8 is a flow chart of a general method provided by the present disclosure for conducting pulsed behavior modeling with steady state average conditions. The method begins by providing the ATS 10 (FIG. 7), which is programmed to capture at least one behavior of a DUT (step 100). The ATS 10 generates for the DUT 12 (FIG. 7) an input power signal having an input pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level (step 102). Next, the ATS 10 captures via the behavior sensor 18 (FIG. 7) at least one behavior of the DUT 12 while the input power is at a predetermined pulse level (step 104). The ATS 10 then steps the predetermined pulse level to a different predetermined pulse level (step 106). The step in pulse level is typically an increment or decrement of a desired amount such as 1 dB. The ATS 10 then determines if a desired range of predetermined pulse levels has been swept (step 108). If not, steps 102 through 108 are repeated for the next predetermined pulse level. If yes, the ATS 10 steps the predetermined steady state level to a different steady state level (step 110). The ATS 10 then determines if a desired range of predetermined steady state levels has been swept (step 112). If not, steps 102 through 112 are repeated for the next predetermined pulse level. If yes, the ATS 10 ends the method (step 114). The captured behavior data is then usable to derive a model behavior for the DUT.
FIGS. 9A and 9B make up a flow chart of an extended method for conducting pulsed behavior modeling with steady state average conditions. In particular, the extended method adds pulse modeling of PA behavior under envelope tracking conditions. The extended method begins by providing the ATS 10 (FIG. 7), which is programmed to capture at least one behavior of a DUT (step 200). The ATS 10 generates for the DUT 12 (FIG. 7) a supply voltage signal having a supply voltage pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level (step 202). Then, the ATS 10 generates for the DUT 12 (FIG. 7) an input power signal having an input power pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level (step 204). Next, the ATS 10 captures via the behavior sensor 18 (FIG. 7) at least one behavior of the DUT 12 while the supply voltage and input power are at the predetermined pulse levels (step 206). The ATS 10 then steps the predetermined input power pulse level to a different predetermined input power pulse level (step 208). The step in pulse level is typically an increment or decrement of a desired amount such as 1 dB. The ATS 10 then determines if a desired range of predetermined input power pulse levels has been swept (step 210). If not, steps 204 through 210 are repeated for the next predetermined input power pulse level. The ATS 10 then steps the predetermined supply voltage pulse level for the DUT 12 to a different predetermined supply voltage pulse level (step 212). The step in supply voltage level is typically an increment or decrement of a desired amount such as 1 V. The ATS 10 then determines if a desired range of predetermined supply voltage pulse levels has been swept (step 214). If not, steps 202 through 214 are repeated for the next predetermined supply voltage pulse level. The initial predetermined input power pulse level is also re-established. If yes, the ATS 10 steps the predetermined steady state input power level to a different steady state input power level (step 216). The ATS 10 then determines if a desired range of predetermined steady state input power levels has been swept (step 218). If not, steps 202 through 218 are repeated for the next predetermined steady state input power level. The initial predetermined input power pulse level and initial predetermined supply voltage pulse level are also re-established. If yes, the ATS 10 steps the predetermined steady state supply voltage level to a different steady state supply voltage level (step 220). The ATS 10 then determines if a desired range of predetermined supply voltage levels has been swept (step 222). If not, steps 202 through 222 are repeated for the next predetermined steady state supply voltage level. The initial predetermined input power pulse level, initial predetermined supply voltage pulse level, and initial predetermined steady state input power level are also re-established. If yes, the ATS 10 ends the extended method (step 224). The captured behavior data is then usable to derive a model behavior for the DUT.
Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

## Claims

1. A method for pulsed behavior modeling of a device under test (DUT) comprising:
generating for the DUT an input power signal having an input power pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level;
capturing at least one behavior of the DUT while the input power is at the predetermined pulse level;
stepping the predetermined pulse level to a different predetermined pulse level;
repeating the above steps until a range of predetermined pulse levels is swept;
stepping the predetermined steady state level to a different steady state level; and
repeating the above steps until a range of predetermined steady state levels is swept.

2. The method of claim 1 wherein the DUT is a power amplifier (PA).

3. The method of claim 2 wherein the at least one behavior is amplitude modulation-amplitude modulation (AMAM) behavior for each predetermined steady state level and each predetermined pulse level.

4. The method of claim 2 wherein the at least one behavior is amplitude modulation-phase modulation (AMPM) behavior for each predetermined steady state level and each predetermined pulse level.

5. The method of claim 1 wherein the range of predetermined pulse levels is from around −30 dBm to around 10 dBm.

6. The method of claim 5 wherein an iterative step of predetermined pulse level is around 1 dB while stepping the predetermined pulse level to a different predetermined pulse level.

7. The method of claim 1 wherein the range of predetermined steady state levels is from around −20 dBm to around 10 dBm.

8. The method of claim 7 wherein an iterative step of predetermined steady level is around 10 dB.

9. The method of claim 2 wherein the range of predetermined steady state levels is only one steady state level of input power for an envelope tracking system.

10. The method of claim 9 further including a step of setting a predetermined average PA supply voltage in association with generating the input power signal for the DUT.

11. The method of claim 10 further including stepping a predetermined PA supply voltage pulse level to a different predetermined PA supply pulse level is associated with stepping the predetermined steady state level to a different steady state level.

12. A tangible computer-readable medium having instructions stored thereon, wherein the instructions are readable by a computing device of an automated test system to perform operations for pulsed behavior modeling of a device under test (DUT), the operations comprising:
generating for the DUT an input power signal having an input power pulse that transitions from a predetermined steady state level to a predetermined pulse level and back to the predetermined steady state level;
capturing at least one behavior of the DUT while the input power is at the predetermined pulse level;
stepping the predetermined pulse level to a different predetermined pulse level;
repeating the above steps until a range of predetermined pulse levels is swept;
stepping the predetermined steady state level to a different steady state level; and
repeating the above steps until a range of predetermined steady state levels is swept.

13. The tangible computer-readable medium of claim 12 wherein the DUT is a power amplifier (PA).

14. The tangible computer-readable medium of claim 13 wherein the at least one behavior is amplitude modulation-amplitude modulation (AMAM) behavior for each predetermined steady state level and each predetermined pulse level.

15. The tangible computer-readable medium of claim 13 wherein the at least one behavior is amplitude modulation-phase modulation (AMPM) behavior for each predetermined steady state level and each predetermined pulse level.

16. The tangible computer-readable medium of claim 12 wherein the range of predetermined pulse levels is from around −30 dBm to around 10 dBm.

17. The tangible computer-readable medium of claim 16 wherein an iterative step of predetermined pulse level is around 1 dB while stepping the predetermined pulse level to a different predetermined pulse level.

18. The tangible computer-readable medium of claim 12 wherein the range of predetermined steady state levels is from around −20 dBm to around 10 dBm.

19. The tangible computer-readable medium of claim 18 wherein an iterative step of predetermined steady level is around 10 dB.

20. The tangible computer-readable medium of claim 13 wherein the range of predetermined steady state levels is only one steady state level of input power for an envelope tracking system.

21. The tangible computer-readable medium of claim 20 further including a step of setting a predetermined average PA supply voltage in association with generating the input power signal for the DUT.

22. The tangible computer-readable medium of claim 21 further including stepping a predetermined PA supply voltage pulse level to a different predetermined PA supply pulse level is associated with stepping the predetermined steady state level to a different steady state level.