Agilent 5991-4607EN Solutions for RF Power Amplifier Test - Application Note c20140923 [8] free download

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Keysight Technologies Solutions for RF Power Amplifier Test Application Note 02 | Keysight | Solutions for RF Power Amplifier Test - Application Note Making Faster, Repeatable RF Power Amplifier Tests with Envelope Tracking and Digital Pre-Distortion Using a Range of Test System Techniques, and Modular Signal Generation and Analysis. Overview As wireless mobile devices grow in capability and complexity, the associated growth in power demand is driving new approaches to battery utilization and power efficiency. One of the single largest power consumers in a wireless handset is the RF Power Amplifier (PA) and as such, improved efficiency tech- niques like Envelope Tracking (ET) and Digital Pre-Distortion (DPD) are being increasingly utilized. The key implication for test engineers--whether in design, characterization or manufacturing test--is that testing these devices with this additional capability can potentially drive up both test cost and overall test time. This application note will discuss various approaches to maximizing test equipment utiliza- tion and reducing test times for such component RF PA's and front-end modules. Problem The demand for higher test speed spans from design validation to production test. As RF PAs sup- port multiple modes, frequency ranges, and modulation formats there is more to test during the validation phase. Thousands of tests are not uncommon. During RF PA production test, manufac- turers have to deal with a number of critical issues; namely, speed, repeatability, cost, maintain- ability, and upgradability. Their biggest stress, however, comes from trying to balance speed and repeatability. Typically as test speed increases, repeatability decreases. Manufacturers must constantly struggle to balance these issues, while also keeping an eye on cost and maintainability. Addressing the speed challenge is further complicated by the fact that PAs are being manufactured in increasingly higher volumes to meet the demand for more and more wireless mobile devices, and have grown even more complex. Techniques like DPD and envelope tracking are often employed to help linearize the PA and increase its power efficiency, but these techniques only add to the testing that's necessary during production, further slowing down the process. With PA manufacturers looking to reduce overall test times from 1.5 seconds, to 500 ms or less, these slow-downs are simply no longer acceptable. Solution The key to addressing the challenges now facing PA validation and manufacturing teams lies in finding a way to increase test speed, while maintaining repeatability. Luckily, a number of test sys- tem techniques are now available to manufacturers for just such a task. The first technique involves speeding up the PA power servo loop (Figure 1). A power servo loop is essentially a "test and adjust" process. The engineer sets the RF input power level to the Device- Under-Test (DUT), then checks the