Recommendations for the extraction of the frequency response H0(jωS)

This section reviews some recommendations for extracting a frequency response in order to apply a stability analysis with the STAN tool. For more information, please see the Application Note "Frequently Asked Questions About Nonlinear Stability Analysis When Using STAN Tool"

  1. During the sweep, the frequency of the small-signal current generator must not exactly overlap with the large-signal fundamental frequency (or with any of its harmonics). Just one hertz apart is enough for correct operation. This is already considered in the ADS templates for large-signal stability analysis.
  2. When working with ADS, we strongly recommend the use of the ADS templates to get the frequency response, especially for large-signal stability analysis. These templates are prepared, so the user only needs to choose the node for the analysis and the bandwidth for the frequency sweep.
  3. Selecting the circuit node for the analysis: in general, the closer the node of analysis is to the non-linear element responsible for the oscillation, the highest the controllability and observability (highest sensitivity) for the identification. Nevertheless, exact pole-zero cancellations are likely to happen at some nodes of the power combining structures when odd-mode oscillations are present in multistage power amplifiers. Therefore, at least one analysis per stage is recommended (STAN Tool multi-node analysis), like in the figure below For more information, please see the Technical Note “Selecting the Node: understanding and overcoming pole-zero quasi-cancellations"
    • For circuit with a clear feedback strcuture (amplifiers, oscillators, etc...) an analysis at a single node can be sufficient.
    • For Multi-Stage power amplifiers, at least one analysis per stage is recommended.
    Figure: Recomendation for analysis of a multi-stages design


  4. The frequency resolution is given by the number of points considered in the frequency sweep. The required frequency resolution depends on the dynamics of the analyzed circuit and varies from case to case. The number of points for the frequency sweep is not limited.
  5. Generic files: When a Tool other than ADS is used for simulation, the frequency response must be formatted in a three-column text file (either freq-real-imag or freq-mag-phase). STAN Tool can directly read these “generic” files (without header).