Power Amplifier Characterization Based on LabVIEW Software and PXI Modular Instruments

challenge:

Reduce characterization time for increasingly complex wireless power amplifiers (PAs) without sacrificing measurement accuracy or increasing equipment cost.

Solution:

Using NI LabVIEW software and NI PXI modular instruments to develop a power amplifier characterization system has enabled us to increase test throughput by 10 times while reducing capital equipment costs, power consumption, and physical space.

"Using NI PXI, we were able to reduce the time it takes to characterize a new component from two weeks to about one day."

Challenges of Existing Power Amplifier Characterization Techniques

Although wireless RF power amplifiers are primarily designed to operate in a single frequency band and in a single mode, modern power amplifiers have to meet more diverse requirements. In fact, modern power amplifiers are designed to operate in eight or more frequency bands and can be used for multiple modulation types including GSM, EDGE, WCDMA, HSPA+, LTE, etc.

At TriQuint Semiconductor, we need to test increasingly complex components at multiple frequencies, voltage levels, temperatures, and power ranges. A complete characterization of a typical component requires approximately 30,000 to 40,000 lines of data to fully test the design. Using traditional rack-based RF test equipment, each line of data takes approximately 10 seconds to collect, which would require more than 110 hours to test each individual component.

Designing a Replacement PXI Test System

To address the challenge of reducing the time required to characterize RF components, we developed a power amplifier characterization test system based on NI PXI, LabVIEW, and NI TestStand. Our power amplifier test bench includes 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-4110 programmable power supply

• NI PXI-4130 Power Source Measure Unit

• NI PXI-2596 Dual 6x1 26 GHz Multiplexer

•100 Mbit/s digital I/O modules

• Traditional rack-mount spectrum analyzer

• External power meter, power supply

•LabVIEW

•NI TestStand

• NI GSM/EDGE Measurement Suite

• NI Measurement Suite for WCDMA/HSPA+

We updated the existing test plan using LabVIEW software to complete the same measurement sequence on the NI PXI test bench. Because the measurements are faster on the PXI test system, we configured the characterization sequence to use the PXI test bench whenever possible and use traditional rack instrumentation only when necessary.

Benefits of NI PXI

The main reason for deciding to use PXI was the ability to achieve higher measurement speeds without sacrificing measurement accuracy. Typically, on previous RF amplifier test benches, the time required for RF measurements accounts for the vast majority of the total characterization time. PXI takes advantage of high-speed data buses, high-performance multicore CPUs, and parallel measurement algorithms to achieve the fastest possible test speeds. In addition, the NI GSM/EDGE Measurement Suite and the NI Measurement Suite for WCDMA/HSPA+ use synthetic measurements, and all measurements can be completed using a single set of I/Q data. Using these toolkits, we are able to measure power amplifier characteristics such as gain, efficiency, flatness, ACP, ACLR, EVM, and PVT.

Results using PXI

By using PXI to perform most of the measurements in the PA test bench, we reduced the PA characterization time from two weeks to approximately 24 hours. In addition, we observed significant measurement time improvements in each of the GSM, EDGE, and WCDMA measurement tests. Table 1 compares the measurement time and speed improvements of the traditional test bench and the PXI test bench.

In a single measurement sequence, the PXI test bench completed 6 to 11 times faster. Times are based on 100-frame measurements.

in conclusion

Because we used NI PXI modular instruments, we were able to significantly reduce the time it takes to characterize our RF power amplifiers without sacrificing measurement accuracy. We built our new PXI test system at the same or lower cost than our original traditional instrumentation solution. We also anticipate using NI PXI in future test systems.