7 research outputs found
Stability analysis of RF amplifiers based on MIMO pole-zero identification
No full textSpurious oscillations are one of the principal issues faced by microwave and RF circuit designers. The rigorous detection of instabilities or the characterization of measured spurious oscillations is still an ongoing challenge.
This project aims to create a new stability analysis CAD program that tackles this chal-
lenge. Multiple Input Multiple Output (MIMO) pole-zero identification analysis is introduced on the program as a way to create new methods to automate the stability analysis process and to help designers comprehend the obtained results and prevent incorrect interpretations. The MIMO nature of the analysis contributes to eliminate possible controllability and observability losses and helps differentiate mathematical and physical quasi-cancellations, products of
overmodeling.
The created program reads Single Input Single Output (SISO) or MIMO frequency response
data, and determines the corresponding continuous transfer functions with Vector Fitting. Once the transfer function is calculated, the corresponding pole/zero diagram is mapped enabling the designers to analyze the stability of an amplifier.
Three data processing methods are introduced, two of which consist of pole/zero elimina-
tions and the latter one on determining the critical nodes of an amplifier. The first pole/zero elimination method is based on eliminating non resonant poles, whilst the second method eliminates the poles with small residue by assuming that their effect on the dynamics of a system is small or non-existent. The critical node detection is also based on the residues; the node at which the effect of a pole on the dynamics is highest is defined as the critical node.
In order to evaluate and check the efficiency of the created program, it is compared via
examples with another existing commercial stability analysis tool (STAN tool).
In this report, the newly created tool is proved to be as rigorous as STAN for detecting instabilities. Additionally, it is determined that the MIMO analysis is a very profitable addition to stability analysis, since it helps to eliminate possible problems of loss of controllability,
observability and overmodeling
Stability analysis of RF power amplifiers through MIMO pole-zero identification techniques.
No full text163 p.El amplificador de potencia es un componente clave en la arquitectura de los transmisores de comunicaciones inhalámbricas. La complejidad de las señales de los sistemas de comunicación actuales impone unas especificaciones exigentes en el diseños de los mismos. Es por ello que los ciclos de concepción de los circuitos de microondas son en general lentos y muy costosos.Desafortunadamente, la aparición indeseada de oscilaciones al medir las prestaciones de los amplificadores de potencia de radio-frecuencia y microondas es un problema muy común al que se enfrentan los diseñadores. Un amplificador de potencia diseñado sin llevar a cabo análisis rigurosos de estabilidad puedes ser inestable, y ello puede llevar a la generación de oscilaciones que impiden el correcto funcionamiento del amplificador y pueden incluso llegar a destruirlo completamente o quemarlo
Understanding the Effect of Long-Term Memory Model Parameters in Pole-Zero Identification for Stability Analysis of Power Amplifiers
No full text[EN] Understanding the nature of potential instabilities is indispensable for the stabilization of power amplifiers (PAs). Pole-zero identification is one of the techniques that can be used to determine the stability of a design in large-signal operation. In this work, the possible presence of poles at the fundamental frequency linked to the long-term memory parameters of the transistor’s model (self-heating and traps) is presented and discussed. The paper shows how their effect on the identified frequency responses around the fundamental frequency may compromise the stability analysis results and the assessment of stability margins. The low observability of the poles at the fundamental frequency highlights the importance of an accurate identification of real poles in low-frequency bands. A specific algorithm for the automatic frequency domain identification of non-resonant frequency responses and a procedure for detecting and reducing overfitting of real poles is proposed in this article. The benefits of the proposed methodology to correctly detect and analyze real poles at low frequencies is demonstrated through Monte-Carlo (MC) sensitivity analyses of two different amplifier designs.This work has been funded by MCIN/AEI/10.13039/501100011033, Grant PID2019-104820RB-I00 and partially funded by the Departamento de Educación del Gobierno Vasco (IT1533-22)
Efficient Calculation of Stabilization Parameters in RF Power Amplifiers
No full textThis article proposes an efficient method for the calculation of the stabilization parameters in RF power amplifiers operating in periodic large-signal regimes. Stabilization is achieved by applying the principles of linear control theory for periodic linear time-varying (PLTV) systems. A numerical method is proposed to obtain the harmonic transfer function that represents the system linearized around the large-signal steady state. Then, a feedback analysis is performed to calculate the closed-loop poles of the PLTV system. The proposed approach is demonstrated with two examples. First, a three-stage amplifier that exhibits a low-frequency oscillation for increasing values of input power is correctly stabilized. Next, the stabilization of an unstable design that exhibits an odd-mode parametric oscillation is presented. The results of the proposed technique are compared to those obtained with the conventional parametric stability simulation. These examples serve to illustrate the capability and efficiency of the proposed approach.This work was supported in part by the Spanish Administration under Project PID2019-104820RB-I00 and in part by the Basque Country Government under Project IT1104-16
Detecting Critical Resonances in Microwave Amplifiers through Noise Simulations
No full textThe presence of critical resonances in microwave power amplifiers has a negative impact on its behavior and performance. These critical resonances are usually predicted from pole-zero stability simulations. In this paper, a different and less demanding approach for the circuit designer is proposed. It is based on performing noise simulations of the amplifier and observing the rise in the noise spectrum that happens when the system has low damping poles. Critical resonance detection is simplified since no additional probes have to be inserted in the circuit and no post-processing for pole-zero analysis is required. The technique is applied to two amplifier prototypes fabricated in microstrip hybrid technology and the results are compared with the conventional pole-zero approach.This work was supported in part by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund under Research Project TEC2015-67217-R and in part by Basque Country Government under Project IT1104-16
In-Circuit Characterization of Low-Frequency Stability Margins in Power Amplifiers
No full textLow-frequency resonances with low stability margins affect video bandwidth characteristics of power amplifiers. In this paper, a non connectorized measurement technique is presented to obtain the low-frequency critical poles at internal nodes of a hybrid amplifier. The experimental setup uses a high-impedance probe connected to a vector network analyzer to obtain a fully calibrated closed-loop frequency response that is identified to get the poles of the device at low frequency. Compared to previous connectorized solutions, the approach avoids the ad hoc insertion of extra RF connectors to access the low-frequency dynamics of the amplifier. In addition, it simplifies the characterization at multiple internal nodes, which is worthwhile for an efficient detection and fixing of critical low-frequency dynamics in multistage power amplifiers. The technique is first applied to dc steady-state regimes and compared to the connectorized approach on a single-stage amplifier. Next, it is applied to a three-stage amplifier to show its potential to detect the origin of the undesired dynamics and the most effective way to increase stability margin. Finally, the technique has been extended to the large-signal case to increase its usefulness for the design and diagnosis of high-power amplifiers.This work was supported in part by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund under Research Project TEC2015-67217-R and in part by Basque Country Government under Project IT1104-16
Stability analysis with Pole-zero Identification: unveiling the critical dynamics of microwave circuits
No full textThe term pole-zero identification refers to obtaining the poles and zeros of a linear (or linearized) system described by its frequency response. This is usually done using optimization techniques (such as least squares, maximum likelihood estimation, or vector fitting) that fit a given frequency response of the linear system to a transfer function defined as the ratio of two polynomials [1], [2]. This kind of linear system identification in the frequency domain has numerous applications in a wide variety of engineering fields, such as mechanical systems, power systems, and electromagnetic compatibility. In the microwave domain, rational approximation is increasingly used to obtain black-box models of complex passive structures for model order reduction and efficient transient simulation. An extensive bibliography on the matter can be found in [3]-[6]. In this article, we focus on a different application of pole-zero identification. We review the different ways in which pole-zero identification can be applied to nonlinear circuit design, for power-amplifier stability analysis, and more. We provide a comprehensive view of recent approaches through illustrative application examples. Other uses for rational-approximation techniques are beyond the scope of this article.This work was supported in part by the French Space Agency (CNES) under projects R-S10/TG-0001-019 and R-S14/TG-0001-019; by a joint Ph.D. research grant from CNES and Thales Alenia Space, France; by project TEC2015-67217-R (MINECO/FEDER); and by the Basque Country Government through project IT1104-16
