EVM stands for error vector magnitude. It is a measure of distortion for a modulated signal. EVM is based on the offset of each sample as represented in the constellation diagram, using the relation of the actual point versus the ideal point.

EVM describes the difference of a measured sample point versus the reference point in a constellation diagram. This difference is called the error vector.

EVM is most commonly measured by using a spectrum or signal analyzer connected to the output of the device under test.

EVM characterization and PA linearization

Q: What is linearization?

Linearization is a method to minimize the distortion as created by non-linear components such as power amplifiers. Digital predistortion s a common example to achieve linearization.

Q: Digital predistortion of power amplifiers for wireless applications

Digital predistortion is a common method for linearization. It pre-compensates the non-linear behavior of a power amplifier and enables improved signal quality and lower bit error rates in wireless applications.

Q: How to calculate error vector magnitude?

EVM is calculated by comparing the length of the red error vector either to the length of the green vector (in the case of a peak or maximum power normalization) or to the length of blue vector (for RMS power normalization).

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Power amplifier verification

In the fast-paced world of wireless connectivity, the demand for higher data rates continues to surge. Complex modulation schemes play a crucial role in meeting this demand. A low error vector magnitude (EVM) at both the component and system levels is key to ensuring that these modulation schemes are robust and stable.

Different use cases call for different modulation schemes. They are tailored to handle a wide range of transmission channels, spanning short to long distances and addressing a wide range of application demands - from high data rates in Wi Fi to lower rates for IoT scenarios. Complex modulations that use high order schemes require extremely low EVM figures to reliably decode transmitted signals.

The radio frequency (RF) frontend - with its active devices - is particularly critical to the EVM capabilities of a complete system. The main nonlinearities that cause EVM degradation come from the RF power amplifier (PA). At the system level, digital pre-distortion (DPD) is used as main linearization method to improve the overall EVM performance.

Rohde & Schwarz stands at the forefront of RF component characterization, offering industry-leading solutions for EVM validation. Numerous EVM reference test platforms around the globe rely on Rohde & Schwarz technology, cementing our position as a trusted partner in ensuring the optimal performance of wireless systems.

Master your EVM measurements

Regardless of product development stage, the focus is always on ensuring compliance with stringent EVM requirements. The primary objectives are:

Meeting design specifications
Providing EVM performance margins to account for production fluctuation
Validating low EVM with target application test signal, according to relevant standards
Monitoring additional KPIs, such as adjacent channel leakage ratio (ACLR)

During design optimization and linearization, the focus is on:

Enhancing the topology and technology of the RF frontend
Striking the right balance between efficiency, output power and gain while meeting the required EVM specifications
Utilizing digital pre-distortion (DPD) for signal performance improvement

In the characterization and production stages, it is important to ensure:

Robust validation of EVM performance
High measurement throughput across output power levels, frequency ranges and various operating conditions
Accuracy vs. cost balance

Discover the best solutions for EVM validation

When it comes to ensuring unparalleled EVM performance and versatility, Rohde & Schwarz solutions stand at the forefront of innovation.

R&S®SMW200A vector signal generator and R&S®FSW signal and spectrum analyzer combo: industry leading EVM performance, high signal bandwidth for any standard, wideband DPD applications
R&S®FSW: advanced noise cancellation to meet the most stringent requirements of Wi Fi 8 signals with 4k QAM
R&S®FExx external frontends: frequency range extended to the terahertz (THz) domain for next generation wireless communication
R&S®FSW-K18 amplifier application: integrated EVM test environment that allows for EVM tests with adjustable test sweep parameters
SCPI recorder in the signal generator and analyzer: simplified automation for development and characterization with automatically generated automation code
R&S®PVT360A performance vector tester: maximum test speed and throughput for fast and efficient EVM validation

Linearization of upcoming high-efficient RF power amplifiers using simulation and hardware measurements

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Linearization of upcoming high-efficient RF power amplifiers using simulation and hardware measurements

Discover advanced methods for boosting RF power amplifier performance and for optimizing broadband RF applications from industry leaders in different video series.

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Benefits of our EVM characterization solutions

Rohde & Schwarz offers leading solutions for RF component characterization. Our solutions support a diverse range of digital systems - from mobile wireless and Wi Fi to wideband custom satellite link systems. Other benefits include:

Expansive frequency coverage - up to THz range
Integrated optimization with digital predistortion
Comprehensive instrument portfolio with options for all requirements and budgets

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