Edouard Ngoya

Envelop transient analysis: a new method for the transient and steady state analysis of microwave communication circuits and systems

The two popular and general purpose simulation techniques, Time Domain Integration and Harmonic Balance, do not fulfil the requirement for analysis of microwave communication systems with arbitrary modulated carrier frequency. A new technique is presented, which overcomes this default. A dramatic saving in computer memory space and computation time is obtained with respect to the previous methods.

Accurate RF and microwave system level modeling of wideband nonlinear circuits

Accurate system level simulation is indispensable for efficient RF communication system design. However system level models of nonlinear circuits are today very limited by their inability to handle nonlinear memory effects. The paper describes a new approach of system-level modeling which accounts efficiently for nonlinear envelope memory effects of wideband amplifiers, multipliers and mixers.

A new behavioral model taking into account nonlinear memory effects and transient behaviors in wideband SSPAs

Accurate and non quasi-static behavioral models of SSPAs taking into account nonlinear memory effects become of prime importance for a breakthrough in system level analysis and design of wideband digital communication systems. This paper describes a new method to characterize and integrate memory effects in nonlinear behavioral models of SSPAs allowing to reproduce both transient and steady state behaviors.

Analysis of low frequency memory and influence on solid state HPA intermodulation characteristics

A theoretical analysis using two-tone simulations and practical measurements of low frequency memory impact on third order intermodulation (IM3) on HBT as well as HFET power amplifiers is carried out. A particular emphasis is placed on the thermal origin for the HBT case and electrical origin for the HFET case of these low frequency nonlinear phenomena.

An improved behavioral modeling technique for high power amplifiers with memory

The introduction of frequency dependence in system level nonlinear behavioral models is of prime importance as wideband signals are going to be massively used with nonlinear SSPA. This paper describes an improved technique to model envelope memory effects for amplifiers exhibiting both high and low frequency memory.

Behavioral modeling of RF and microwave circuit blocks for hierarchical simulation of modern transceivers

The development of simulation and macro-modeling techniques for RF and microwave communication systems has been a high priority research subject for several years. If one observed this last years an impressive improvement of simulation tools performances, the full chip simulation of modern TX-RX chains remains a real stumbling block, as the transistor count has considerably increased. This paper discusses the hierarchical RF simulation issue using the same harmonic balance or envelope transient simulation engine for both transistor level description and circuit block macro-models. This method can reduce the size of the problem to enable accurate and fast simulation of large size circuits. The concept requires however to develop macro-modeling techniques taking into account impedance mismatch effects, which are discussed here.

Measurement based modeling of power amplifiers for reliable design of modern communication systems

The characterization and the modeling of nonlinear memory effects are, nowadays, an integral part of the design process of modern communication systems. Notably, the nonlinear long term memory effects occurring in solid state devices impact considerably system performances. Recently, a new method to characterize and integrate low frequency memory effects in nonlinear behavioral models of SSPAs has been presented. This paper presents a detailed mathematical study and a measurement based extraction principle of the proposed behavioral model. Calibrated time-domain envelope measurements are used for the model extraction and verification procedures. The extraction technique is illustrated by the modeling of a L-Band HFET amplifier.

On the Continuous-Time Model for Nonlinear-Memory Modeling of RF Power Amplifiers

The RF front-end in modern communication systems is faced with variable envelope and large bandwidth signals (including desired signals and large interferers), which require the behavioral model of the amplifying unit (either in Tx or Rx) to accurately account for nonlinear memory effects. Important advancements have been made on the subject; however it is still challenging to derive a model that performs equally well with all possible input stimuli. This paper gives a concise overview of the recent developments that have been made on the continuous-time modeling approach for the behavioral modeling of nonlinear memory in power amplifiers, as opposed to the explicit discrete-time modeling approach.

Newton-Raphson iteration speed-up algorithm for the solution of nonlinear circuit equations in general-purpose CAD programs

The Newton-Raphson method is usually adopted for the solution of nonlinear circuit equations. However, it is well known that convergence of Newtons scheme is highly dependent on the initial guess, and often fails when convenient modifications are lacking. Typical Newton convergence problems in electronic circuits analysis are identified. An algorithm speeding up the convergence of the Newton scheme and making it less dependent on the initial guess is presented. The method is simple and a general-purpose one, applicable to all kinds of circuit equations. Numerical results are presented, and a comparison with previous work is done.

A Novel Experimental Noise Power Ratio Characterization Method for Multicarrier Microwave Power Amplifiers

The linearity characterization of multicarrier power amplifiers in terms of Noise Power Ratio (NPR) is now well adopted. The use of an analog band pass noise source with a notch in the center bandwidth is currently used for this purpose. We present in this paper a novel NPR measurement technique based on a numerical generation of a gaussian noise. This experimental noise generation is similar to the technique used in non linear circuit level or system level simulations using the envelope transient technique. The measurement principle is based on the use of a baseband arbitrary waveform generator (AWG) and an upconverter chain from baseband to L or S band. The large signal Noise stimuli drive the amplifier under test. The output signal of the amplifier is downconverted back to baseband and the resulting complex envelope is recorded with a sampling scope and computed for NPR extraction. A comparison of NPR measurements obtained with our method and with the conventional analog noise source technique is presented. Other possible applications of our measurement system are also mentioned and emphasize the capabilities of the proposed characterization tool.