Demand for high data throughput and low latency is pushing device specifications and operational standards toward wideband modulation. Wideband performance benefits come with a heavy cost: significantly increased noise.
Increased noise
This noise introduces additional test complexity and measurement uncertainty, which is further exacerbated by the industry’s desire to pack as many modulated signals into the available bandwidth as possible. This not only constrains error vector magnitude (EVM) requirements further, but also degrades system signal-to-noise ratio (SNR).
So, how can users simplify the performance verification process, while ensuring component’s standard compliance?
Simplified measurement set-up
Nizar Messaoudi discusses how to measure an amplifier’s EVM using only a vector network analyzer (VNA)
In part two of webinar series, VNA Active Device Characterization Essentials, Keysight (Keysight Technologies) PNA Product Manager, Nizar Messaoudi, discusses how to measure an amplifier’s EVM using only a vector network analyzer (VNA).
Demonstrating digital demodulation on a sub-6 GHz amplifier, Nizar Messaoudi explains why doing complex modulation scheme EVM measurements on a VNA increases testing pace, by reducing setup complexity.
Using the modulation distortion analysis application to measure the amplifier’s distortion, Nizar also walks-through how to use the VNA’s signal analysis application, in order to capture the amplifier’s EVM to a given constellation and demodulation standard.
Improved measurement quality
While, in the past, these measurements were conducted on a signal analyzer (SA), as Keysight’s Nizar Messaoudi explains, the VNA’s advanced feature set offers various wideband measurement upgrades for component testing.
Beyond test setup simplification, the VNA equips designers with more than just harmonic testing and spur search. When using VNAs, the stimulus signal is always known.
Nizar Messaoudi details how taking advantage of this functionality improves digital image rejection. Additionally, the VNA uses coherent averaging to reduce problematic wideband noise and enable other complex tests, such as noise power ratio (NPR) or even full waveform demodulation.
Upgraded error isolation
Nizar Messaoudi addresses why a designer would want to demodulate waveforms as well
Nizar Messaoudi addresses why a designer would want to demodulate waveforms as well. He explains that EVM is the foremost specification that component vendors must provide for their product.
As standard stringency increases with wideband modulation implementation, vendors want to provide standard specific EVM to their customers. However, to do so effectively requires demodulation.
The VNA use inverse fast Fourier transforms (IFFT) to produce statistically representative compact signals, equivalent to signals of the desired standard (5G NR, Wi-Fi, DBSX2, etc.) and then, measures fully demodulated EVM in the time domain.
Access to the VNA’s multi-receiver architecture
Additionally, access to the VNA’s multi-receiver architecture allows for the measurement of a fully calibrated input signal into the input reference plane. Without isolation of the system error, SAs erroneously assume the measured EVM is that of the DUT.
Alternatively, VNAs measure output signal given the know input signal and perform signal correction on the input reference plan. In doing so, VNAs drive down the residual EVM of the source and deliver the DUT’s distortion EVM isolated from the system error contributions.
Wideband modulation schemes offer many benefits
Wideband modulation schemes offer many benefits, but to successfully create compatible technologies requires designers to deal with wideband noise.
Modern VNA signal analysis’ simplified setup, improved test quality, and upgraded calibration and error isolation uniquely enable realistic and repeatable wideband measurements.
