Understanding the Effect of Long-Term Memory Model Parameters in Pole-Zero Identification for Stability Analysis

Introduction

In power amplifier design, stability analysis is critical to ensuring reliable performance. A key technique for this analysis is pole-zero identification, which determines potential instabilities. However, long-term memory effects, such as self-heating and charge trapping, introduce challenges by affecting pole locations and observability. This blog explores how these memory effects impact pole-zero identification and presents an improved algorithm for accurate stability assessment.

The Role of Long-Term Memory Effects

Power transistors exhibit memory effects due to:

• Self-heating: The gradual temperature increase affects electrical characteristics over time.
• Charge trapping: The accumulation of trapped charges influences device behavior at different time scales.

These effects introduce low-frequency real poles that can be difficult to detect, leading to inaccurate stability assessments. In some cases, commercial pole-zero analysis tools may misidentify these poles, mistaking them for stability-critical elements.

Improved Identification Algorithm

To enhance accuracy, researchers propose a modified pole-zero identification technique with:

• Enhanced detection of real poles: Focuses on identifying slow dynamics caused by long-term memory.
• Reduction of overfitting: Prevents misclassification of poles by refining frequency domain identification techniques.
• Monte Carlo analysis: Assesses variability across different amplifier designs, ensuring robustness.

Practical Applications and Validation

The proposed methodology was tested on a Doherty MMIC amplifier and a medium-power GaN-based amplifier, revealing:

• Improved detection of memory-induced poles.
• Reduced uncertainty in stability margin assessments.
• Better correlation between simulated and real-world performance.

Conclusion

Understanding the impact of long-term memory effects is essential for accurate stability analysis in power amplifiers. By refining pole-zero identification techniques, engineers can make more reliable design decisions, reducing the risk of unexpected oscillations.

How do you currently approach stability analysis in amplifier design? Let us know in the comments!