High Power Amplifier Test Enhancements with the ENA-X VNA

High Power Amplifier Test Enhancements with the ENA-X VNA

5G Component Test Challenges

Advancements in communication systems require higher data rates with ultra-low latency. Engineers must optimize RF component performance-especially for power amplifiers-to successfully implement 5G New Radio (NR) transmitters to meet these requirements.

Characterizing your device under test (DUT) with today's higher data rates requires wideband signals and complex modulation schemes. Manually reconfiguring multiple test setups or automating complex switch-based systems inflates verification cycle time and introduces additional error potential. The signal quality of your test instruments may limit the error vector magnitude (EVM) of the test system - known as the residual EVM. While this degree of inherent error was acceptable in previous communication systems, today's 5G transmission systems need precise measurements to certify performance compliance to stringent EVM requirements (3.5% in 256 QAM to 1% for 1K QAM).

While low-power conditions sufficiently capture linear S-parameters, measurements like gain compression and distortion analysis need high-power input signals. Furthermore, most PA designs will operate close to saturation to optimize power added efficiency (PAE), while maintaining overall system level performance targets. For low power levels, the signal-to-noise or noise figure dominates the EVM and at high power, the EVM is dominated by non-linear distortion.

Figure 1. New technological challenges introduced by 5G NR

Communication Component Characterization Solution

The new Keysight E5081A ENA-X network analyzer platform helps you push through engineering boundaries to develop and deploy power amplifiers faster than ever before. This network analyzer includes integrated modulation distortion analysis software and full vector correction to address input port mismatch, channel power, and source error contributions in a single test setup. Built with custom monolithic microwave integrated circuits (MMICs), the new ENA-X provides repeatable results with high measurement accuracy, so you can connect and calibrate the test setup only once to perform measurements.

By offering advanced integrated low-noise receivers and direct receiver access along with distortion measurements on a single test setup, the ENA-X network analyzer enables component characterization under high-power, complex modulation schemes. These features consolidate the component verification setup necessary to conduct reliable characterization, minimizing test cycle time for amplifiers, mixers, and frequency converters.

Combined with powerful modulation distortion analysis software, previously only available on our highest-performing Keysight PNA Series network analyzers, the mid-range E5081A ENA-X uses spectral correlation to directly analyzes modulated input and output signals in the frequency domain. With wide dynamic range and vector-corrected calibration at the DUT plane addressing input port mismatch, channel power, and source error contributions, the ENA-X offers low residual EVM and enhanced signal fidelity.

High-power test setups needed to complete nonlinear PA characterization require a booster amplifier. Including a booster amplifier in the setup and calibration adds complexity and error potential to the measurement. The ENA-X was designed with these high-power considerations in mind.

The two key benefits that the E5081A offers for high-power PA test are:

• direct receiver access
• receiver attenuators

Direct receiver access

The booster amplifier's reverse isolation or S12, makes accurate DUT S11 measurements and input power or reference receiver drift monitoring difficult on the standard setup. The solution to this high-power setup challenge is to use an external test set, that is, an external dual directional coupler and route the signals to the VNA receivers. ENA-X's configurable architecture allows developers to reroute the signals through a path alternate to the booster amplifier, directly to the ENA-X receivers. This flexibility enables accurate S11 amplifier measurements while using high power signals.

Figure 2. High-power test configuration with a 2-port E5081A. Reflected / transmitted DUT signals are detected with all the logical receivers while the VNA firmware captures high-power S-parameters.

Receiver attenuators

A key consideration for high-power measurements is the test instrument's internal component power-handling capability. High power levels risk damaging the network analyzer, causing costly repairs. Typically, power amplifier test requires external attenuation to protect against potential receiver compression leading to inaccurate measurement and test set damage. However, adding external fixtures to the test set also adds error-potential and calibration complexity. To minimize the risk of instrument damage and simplify measurements, the ENA-X network analyzer consolidates the setup through built-in receiver attenuators, eliminating the need for external attenuators.

Conclusion

Designing power amplifiers compatible with the 5G infrastructure poses significant challenges because of wide bandwidth signals, complex modulation schemes, and increasingly strict EVM requirements. The traditional VSA characterization method no longer satisfies design engineers' needs. The E5081A ENA-X VNA modulation distortion solution provides numerous PA characterization benefits that overcome wideband measurement challenges:

• Wide dynamic range enables low residual EVM because of the lower noise floor.
• Easy calibration for vector-corrected measurements enhances signal fidelity at the DUT input, resulting in significantly improved measurement reproducibility.
• Sophisticated software permits distortion analysis under modulated conditions.

For any PA characterization, a VNA is essential to characterize linear and nonlinear performance. With the MOD application, the test system makes traditional VNA measurements as well as EVM.

The unique architecture of the ENA-X network analyzer allows RF developers to perform multiple multiport measurements on a single simplified setup, improving measurement accuracy and reproducibility, reducing test cycle time, and generating the lowest residual EVM results on the market.

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