Tips for Advanced Network Analysis
2018-10-05 | 5 min read
It requires much more than just S-parameters to completely characterize an active RF device. Complex tests must be set up to find compression, intermodulation distortion (IMD), spurs, and more. Traditionally, multi-instrument RF test systems are created to meet the challenges of active device characterization.
As network analyzers become more advanced and integrated, engineers can simplify their test setups and perform complex characterization in a fraction of the time. We’re going to look at some ways you can fully take advantage of a network analyzer’s advanced features to simplify active device characterization and reduce design cycles.
Active devices such as amplifiers and mixers are intentionally driven into nonlinear operation to maximize their performance. The tradeoff of the increased performance is imperfections from harmonics, intermodulation distortion, and spectral regrowth. The errors generated by one device might be negligible but cascading multiple nonlinear devices will amplify errors. Iterating a design to correct for compounded errors can be costly and time-consuming, especially if your simulation software does not have an accurate nonlinear model of your devices. Hot S-parameters offer quick, but incomplete, analysis of nonlinear operation of your device. A more complete characterization allows you to quickly design matching circuits without guesswork.
Complete nonlinear characterization minimizes design iterations by taking the guesswork out of simulation. You can capture the complete nonlinear behavior of devices using X-parameters. X-parameters are the mathematically correct extension of S-parameters to large-signal conditions. X-parameters provide both magnitude and phase of the fundamental and harmonics. They can be cascaded in simulation to accurately represent gain, group delay, and more for driven components.
Characterize in the Time Domain
As bit rates of digital systems increase, signal integrity of interconnects drastically affects system performance. Fast and accurate analysis of interconnect performance in both the time and frequency domains becomes critical to ensure reliable system performance. Rather than using an oscilloscope for time-domain characterization, use your network analyzer’s Time Domain Reflectometry (TDR) function to convert frequency domain measurements to the time domain with an Inverse Fourier Transform.
Advanced TDR applications for network analyzers contain many helpful features, such as eye diagrams and jitter simulation. One of the most helpful TDR features for active device characterization is Hot TDR. Hot TDR is the TDR and return loss measurement of active devices in the power-on state. Understanding the active impedance of your device minimizes the design iterations needed to pass eye mask tests.
TDR relies on DC extrapolation from low frequency data points. For the most accurate DC extrapolation, use an ECal module with a DC option.
Speed up Characterization with Spectrum Analysis
Traditional mixer and converter characterization and IMD measurements require a spectrum analyzer and external signal generators. Characterizing spurs over wide DUT operating ranges is tedious and time-consuming, especially with multiple pieces of hardware involved.
Take advantage of spectrum analysis on your network analyzer to quickly make spurious measurements and characterize mixers and converters. A single-connection, multiple-measurement capability enables you to see multi-channel spectrum analysis and network analysis simultaneously. This is useful for measuring all of the ports of a mixer, for example. You can also quickly investigate unusual VNA measurements using the Marker-to-SA feature to mark the irregularity then see it on a spectrum display with the same stimulus conditions.
The List Keeps Growing
This is just a small sample of the many features of advanced network analyzers. It’s easy to see how you can replace an entire rack of equipment when you’re able to perform TDR, spectrum analysis, noise figure measurements, and more all from one box.
To learn more about network analyzers, visit the Network Analysis knowledge base.