A. Mallet

Joint optimization of the power-added efficiency and the error-vector measurement of 20-GHz pHEMT amplifier through a new dynamic bias-control method

This paper presents a method for the optimization of the power-added efficiency (PAE), as well as the error-vector measurement (EVM) of a 20-GHz power amplifier (PA) applied in this case to the M quadrature and amplitude modulations. A first key point lies in that both input and output biasing voltages of the solid-state power amplifiers (SSPAs) are dynamically controlled according to the RF power level associated with the symbol to be transmitted. The leading idea is that the dynamic biasing control is designed and implemented to keep fixed amplitude (AM/AM) and phase (AM/PM) conversion values, while the RF input power level changes. The power gain of the PAs can then be dynamically tuned to a fixed power gain corresponding to the compression gain behavior for which the PAE is optimum at low-, medium-, and high-input RF power levels. As a main consequence, PAE performances can be drastically improved as compared to classical backoff solutions and optimized while keeping a very good EVM. A Ka-band hybrid amplifier has been realized using an 8/spl times/75 /spl mu/m power pseudomorphic high electron-mobility transistor. The proposed linearization technique is validated by comparisons between measured PAE and EVM on the SSPA when a fixed and controlled bias are used.

Analysis and elimination of parametric oscillations in monolithic power amplifiers

This work describes an analysis and design methodology for eliminating parametric oscillations in microwave power amplifiers. Large-signal stability analyses based on system pole-zero identification techniques are proposed to guide the design process towards a stable circuit. In order to demonstrate the proposed approach, parametric oscillations of a Ku-band MMIC power amplifier have been eliminated, while maintaining the original performances of the circuit.

Multiport-Amplifier-Based Architecture Versus Classical Architecture for Space Telecommunication Payloads

This paper discusses the suitability of using a multiport amplifier (MPA) for a power section of space telecommunication payloads with power flexibility requirements. The performances of an MPA-based architecture are compared to those of a classical amplification architecture having one power amplifier per beam. This study is based on a 4 times 4 Ka-band MPA composed of four paralleled traveling-wave tube amplifiers (TWTAs). First, a static model of the MPA has been extracted from conventional characterizations. Second, the MPA has been characterized in a realistic environment for telecommunication operation. The good agreement between measured and simulated data serves to validate the MPA model. Once the model has been validated, exhaustive simulations are performed to compare the performances of the MPA-based and classical architectures in terms of power consumption and the TWTAs saturation power. As a result, the MPA approach proves to be an interesting solution because of its greater flexibility, lower power consumption, and lower saturation power required by the TWTAs

Model-order reduction of linear and weakly nonlinear time-varying RF and microwave circuits

Model-order reduction techniques of RF and microwave linear and weakly nonlinear time-varying circuits are presented. The reduced models capture the memory and linear or weakly nonlinear input-output behavior of the circuit, as well as the matching conditions at the model ports. The reported techniques serve to reduce models of a number of RF and microwave functions such as lumped or distributed linear circuits, small-signal amplifiers, mixers, modulators, etc. The reduced models can be implemented in any simulator using standard library components and can be employed both in frequency and time-domain simulations, demonstrating good agreement and significant reduction of simulation time with respect to the simulation of the complete circuit. The model-order reduction techniques are illustrated through different examples.

A new satellite repeater amplifier characterization system for large bandwidth NPR and modulated signals measurements

Power consumption and dissipation of satellite payloads for space telecommunication systems are mainly due to power amplifiers. To increase system capacity with limited bandwidth, multicarrier operations are required. Linearity is specified to limit the signal distortion by the nonlinear power amplifiers. In order to minimize power consumption under those linearity requirements, accurate measurements have to be performed. The NPR is well known as the figure of merit for the intermodulation distortion performance of amplifiers in telecommunications. In this paper, the development of an accurate large bandwidth NPR measurement system is presented. It enables characterizations up to Ka band (17-21 GHz and 27-31 GHz for space telecommunications applications with typically 250 MHz bandwidth). Measurements made on power amplifiers have been used to optimize operating conditions.

A novel behavorial model of power amplifier based on a dynamic envelope gain approach for the system level simulation and design

This paper presents a novel and non quasi static behavioral ( black box) model of power amplifiers. It takes into account nonlinear memory effects for an accurate prediction of signal distortions and power budget in communication systems. The model topology and the model extraction procedure are described. The model proposed in this paper can be derived either from envelope simulation results of a PA circuit design or from time domain envelope measurements of a PA driven by modulated stimuli. Examples of new measurements (i.e. : dynamic AM/AM conversion characteristics) highlight nonlinear memory of SSPAs. The behavioral model proposed is very well suited for an efficient implementation in system level software packages because it consists of an extension of the complex envelope gain function. The proposed complex gain which depends on the input envelope and its first time derivatives provides a great enhancement as compared to the memoryless static complex gain derived from classical AM/AM and AM/PM conversion characteristics.

Efficient nonlinear Stability Analysis of Microwave Circuits using Commercially Available Tools

In this paper, two techniques for checking stability of multi-transistor MMIC circuits are analyzed. The two approaches allow both linear and nonlinear stability analysis of any complex circuit fed by small or large signals. The agreement found gives a unified way to propose a fast and efficient tool to ensure stability of a design during the design step using commercially available software. An example is given to evidence the suitability of the approach. It concerns a MMIC HBT power amplifier, which exhibited a frequency division phenomena that has been detected by simulations and confirmed by measurements.

A fully calibrated four channels time domain RF envelope measurement system for the envelope characterization of nonlinear devices in a load-pull environment

This paper presents a fully calibrated four channels time domain radio-frequency (RF) envelope characterization system. This measurement system enables the acquisition and the vector-correction of the 4 input and output envelope voltage/current waves, including both amplitude and phase, of RF nonlinear microwave devices. The capabilities of the system, when it is associated with passive load pull techniques, are presented to investigate the effects of RF impedance termination on the envelope linearity of mismatched RF nonlinear devices. The proposed measurement set-up is described. Calibration and measurement procedures are detailed. Examples of the 4 fully error corrected time domain envelopes at the input/output RF ports of an optimised gain power MESFET are reported and discussed.

Multi-Port Amplifier Operation for Ka-band Space Telecommunication Applications

This paper discusses the suitability of using a multiport amplifier (MPA) for multimedia multi-beam telecommunication operation with power flexibility requirements. With this aim, a Ka-band MPA has been characterized in a realistic environment for telecommunication operation. Simulation and measurement results are discussed and the performances of the MPA based architecture and a classical architecture (with one power amplifier per beam) is compared in terms of power consumption. The MPA proves to be an interesting solution since it offers flexibility with lower power consumption and less equipment

LTV Circuit Modelling Techniques for System Simulation. Application to a MMIC K-Band I-Q Signal-Modulator

A technique for modelling LTV circuits with frequency-translation such as mixers and signal modulators is presented. The time and frequency-domain simulations of these comp lex circuits can be very expensive in terms of computational resources. A black-box reduced modelling approach for system simulation is proposed. The model consists of an equivalent linearized low-pass filter followed by a memoryless multiplication. The reduced model provides a noticeable decrease of simulation time, with a slight loss of accuracy. The modelling technique has been applied to a MMIC QPSK signal-modulator in K band and implemented in a standard simulation tool. The simulation results of the reduced model and the complete modulator equivalent circuit have been compared, obtaining good agreement.