Qorvo is a leader in high-performance RF solutions for sophisticated mobile devices, defense and aerospace applications, and network infrastructure. Today, Qorvo delivers innovative solutions using GaAs, GaN, SAW, and BAW technologies to organizations around the world. Engineers and scientists rely on Qorvo's innovation to improve the performance and lower the overall cost of their applications.
Challenges With Existing PA Characterization Techniques
While cellular RF PAs were primarily designed to be single band and single mode, today’s PAs are required to meet a much more diverse set of requirements. In fact, modern PAs are designed to operate in eight or more frequency bands, as well as to handle multiple modulation types including GSM, EDGE, WCDMA, HSPA+, LTE, and more.
At Qorvo, we needed to test these increasingly complex parts across a wide range of frequencies, voltage supply levels, temperatures, and power ranges. The complete characterization process for a typical part requires 30,000–40,000 lines of data to completely test the design. Using traditional rack-and-stack RF test equipment, it took us roughly 10 seconds to collect each line of data, which required more than 110 hours of testing for each individual part.
Designing a Replacement PXI Test System
To address the growing challenge of reducing test time in RF part characterization, we developed a PA characterization test system based on NI PXI, LabVIEW, and NI TestStand. Our PA test bench included the following instruments:
- NI PXIe-5673 6.6 GHz vector signal generator
- NI PXIe-5663 6.6 GHz vector signal analyzer
- NI PXI-5691 8 GHz programmable RF amplifier
- NI PXIe-5122 100 MS/s high-speed digitizer
- NI PXI-2596 dual 6x1 26 GHz multiplexer
- 100 Mbit/s digital I/O module
- Traditional rack-and-stack spectrum analyzer
- External power meter, power supplies
- NI TestStand
Using LabVIEW software, we updated our existing test plans to perform the same sequence of measurements on the NI PXI test bench. Because measurement speeds were faster on the PXI test system, we configured our characterization sequences to use the PXI bench whenever possible, augmenting it with traditional rack-and-stack instruments only as necessary.
Advantages of NI PXI
One of the primary drivers behind the decision to use PXI was our ability to achieve faster measurement speed without sacrificing measurement accuracy. In general, the time required for RF measurements on our previous PA test benches dominated the overall characterization time. By using NI PXI, we took advantage of several key technologies that allow PXI systems to achieve faster measurement times. PXI takes advantage of a high-speed data bus, high-performance multicore CPUs, and parallel measurement algorithms to achieve the fastest test times possible. In addition, the NI GSM/EDGE Measurement Suite and the NI Measurement Suite for WCDMA/HSPA+ use composite measurements so that all measurements can be taken on a single set of I/Q data. Using these toolkits, we were able to measure PA characteristics such as gain, efficiency, flatness, ACP, ACLR, EVM, and PVT.
Results From Using PXI
By using PXI to perform the bulk of the measurements on our PA test bench, we shortened the characterization time of our PAs from two weeks to about 24 hours. Also, we observed significant improvements in measurement time for each of our GSM, EDGE, and WCDMA measurement tests. Table 1 compares the measurement times and speedup of both the traditional and the PXI test benches.
As a result of using NI PXI modular instruments, we significantly reduced the characterization time of our RF PAs without sacrificing measurement accuracy. We built the new PXI test systems at the same or lower cost than the original traditional instrument solution. We anticipate using NI PXI for future test systems.