Meeting EVM Challenges with Higher Bandwidths in RF Testing

The evolution of wireless communication technologies, encompassing both cellular and non-cellular standards, is driven by increasing demands for faster data rates, higher signal bandwidths, and greater spectral efficiency. These advancements have introduced the adoption of higher-order modulation schemes, such as 256-QAM and beyond, as well as wider channel bandwidths exceeding 100 MHz. Consequently, the requirements for Error Vector Magnitude (EVM) performance have become significantly more stringent, compelling RF measurement setups and chip/component characterization methodologies to adapt to these evolving challenges.

# The Shift Towards Higher Signal Bandwidths

• Growing Bandwidth Needs: The rollout of 5G NR (New Radio) and Wi-Fi 6/6E/7 has pushed signal bandwidth requirements to new limits, with bandwidths reaching up to 400 MHz in some cases for Wi-Fi 7 and 5G FR2 (mmWave). This trend allows for faster data transmission but increases complexity in ensuring signal integrity.
  
  
• Impact on EVM: With higher bandwidths, the spectral purity and linearity of RF components such as amplifiers, mixers, and transceivers must improve to meet tighter EVM specifications. Small errors in design, noise, or non-linearity can have a significant impact on the overall system performance.
  
  

# Higher-Order Modulation Schemes

• Adoption of Complex Modulations: To maximize spectral efficiency, modern communication systems increasingly use higher-order modulation schemes such as 64-QAM, 256-QAM, and even 1024-QAM. These schemes allow more data to be transmitted per symbol but are more sensitive to noise, distortion, and phase errors.
  
  
• EVM Stringency: As modulation order increases, EVM becomes a critical metric for system performance. For example, 256-QAM systems require EVM values to be less than ~3%, while 1024-QAM systems demand even tighter tolerances. Achieving such low EVM levels necessitates precision in both component design and measurement setups.

# Challenges in Measurement Setups

• Dynamic Range and Linearity: RF measurement equipment, including signal generators and spectrum analyzers, must provide superior dynamic range and linearity to accurately measure the performance of components under these tighter requirements. Any distortion or noise introduced by the test equipment can compromise the measurement results.
  
  
• Phase Noise Control: High-order modulation schemes are highly sensitive to phase noise. Measurement setups must include low-phase-noise oscillators to ensure that phase errors are minimized during testing.
  
  
• Wideband Measurements: Wider signal bandwidths require test equipment with sufficient instantaneous bandwidth to capture and analyze the entire signal. Legacy equipment may not support the required bandwidths for 5G FR2 or Wi-Fi 7, necessitating upgrades to modern test solutions.
  
  
• Multi-Domain Testing: The coexistence of cellular and non-cellular standards in shared spectrum environments demands simultaneous time, frequency, and modulation domain measurements.

# RF Component and Chip Characterization

• Amplifiers and Mixers: Amplifiers must demonstrate high linearity and low noise figure to meet EVM targets, especially for high-bandwidth, high-order modulated signals. Nonlinearities in mixers can introduce significant distortions that degrade EVM.
  
  
• Power Amplifiers (PAs): Efficiency and linearity are competing factors in PA design. Techniques like digital predistortion (DPD) are increasingly used to meet stringent EVM requirements while maintaining efficiency. Measurement setups must support DPD characterization.
  
  
• Transceivers: Modern transceivers must support multi-band, multi-standard operation. Their characterization requires advanced measurement setups capable of testing all relevant parameters, including EVM, adjacent channel leakage ratio (ACLR), and phase noise, across different frequency bands.

# Meeting the Evolving EVM Performance Requirements

To address these challenges, test and measurement equipment must evolve alongside the technologies they are designed to evaluate. Key advancements include:

• Wideband Signal Analysis: Modern vector signal analyzers now support instantaneous bandwidths up to 1 GHz, enabling precise characterization of wideband signals.
  
  
• High-Precision Signal Generators: These generators are capable of producing ultra-clean signals with minimal phase noise and distortion, ensuring accurate EVM testing for high-order modulations.
  
  
• Automation and AI: Automated measurement systems leveraging AI algorithms can optimize setups, reduce human error, and improve the repeatability of EVM measurements across a wide range of conditions.
  
  
• 5G-Specific Solutions: Dedicated 5G test solutions now integrate multi-domain analysis to evaluate EVM, ACLR, and beamforming simultaneously for FR1 and FR2 applications.

#  Implications for Industry Stakeholders

• Chip Manufacturers: The pressure to deliver components with exceptional performance while meeting tight cost and size constraints is increasing. Advanced testing methods during the design and production stages are critical to ensure compliance with stringent EVM requirements.
  
  
• Network Operators: Ensuring low EVM is essential for delivering high-quality services, particularly for applications like ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) in 5G networks.
  
  
• Test and Measurement Providers: Companies providing RF test solutions must continually innovate to stay ahead of evolving standards, ensuring their equipment meets the performance requirements of modern communication systems.

The transition toward higher signal bandwidths and higher-order modulation schemes in cellular and non-cellular standards is reshaping the requirements for EVM performance and RF testing methodologies. As EVM stringency increases, measurement setups and RF component characterization must adapt to ensure precision, accuracy, and compliance with evolving standards. The ability to meet these challenges will be critical for enabling the next generation of wireless communication technologies, from 5G and Wi-Fi 7 to future advancements in AI-driven wireless systems.