Showing papers by "Ángel Mediavilla Sánchez published in 2001"

Smoothing the canonical piecewise-linear model: an efficient and derivable large-signal model for MESFET/HEMT transistors

Abstract: In this paper we present the smoothed piecewise-linear (SPWL) model as a useful tool in the device modeling field. The SPWL model is an extension of the well-known canonical piecewise-linear model proposed by Chua, which substitutes the abrupt absolute value function for a smoothing function (the logarithm of hyperbolic cosine), thus providing the model with several interesting properties. In particular, this function makes the model derivable, which is important to predict the intermodulation distortion behavior. Moreover, it allows one to control the smoothness of the global model by means of a single smoothing parameter. The parameters of the model are adapted to fit the nonlinear function, while the smoothing parameter is selected according to derivative constraints. The applied learning algorithm is a second-order gradient method. The proposed SPWL model is successfully applied to model a microwave HEMT transistor under optical illumination using real measurements. The model receives as input the bias voltages of the transistor, the instantaneous voltages, and the optical power and provides the drain to source current. The performance and computational burden of the SPWL model is compared with an empirical model and with some neural networks-based alternatives.

Demostrador del módulo posterior del radiómetro de 30 GHZ de Planck

Abstract: A radiometer back end module based on broadband low noise amplifiers and band pass filters is presented. Low noise amplifiers are multistage HEMT MMIC chips. A 20% of bandwidth at 30 GHz have been achieved. The passband is fixed by coupled lines microstrip filters. A complete module containing two identical branches of amplification and filtering stages with a gain greater than 30 dB has been developed. The low 1/f noise behavior of gain fluctuations allows the module to be used as the back end module for the differential radiometers in the european scientific mission Planck. Details of the MMICs chips and filters assembly as well as experimental results are included.

AMPLIFICADORES MMIC EN LA BANDA Ka DE BANDA ANCHA

Abstract: This paper describes the design and assembly of two low noise wideband monolithic Ka-Band amplifiers. The designs are fully monolithic. Philips Microwave Limeil ED02AH process, which employs a 0.2 µm Pseudomorphic-High Electron Mobility Transistor (P -HEMT) was the technology chosen. One amplifier has four stages and the other has three stages. A first stage with inductive source feedback has been used to achieve a low noise performance with reasonable gain and return loss and parallel feedback has been used in the last stages to give an upward slope to the gain. The circuit has been measured in a home made test fixture with ridged waveguide (WR-28) own designed transitions to couple the signal from waveguide to microstrip. A gain greater than 12 dB with an average noise of 4.1 dB from 28 to 40 GHz and a minimum noise figure of 2.3 dB at 28.5 dB was measured for the three stages MMIC amplifier. A gain greater than 20 dB with an average noise of 2.3 dB from 28 GHz to 36 GHz and a minimum noise figure of 1.8 dB at 29.5 dB was measured for the four stages MMIC amplifier. 1. INTRODUCCION Los sistemas de comunicaciones que requieren grandes capacidades en la banda milimetrica estan teniendo un gran desarrollo como por ejemplo los sistemas de banda ancha para la distribucion de senales de video sin cable tales como LMDS (Local Multipoint Distribution System) que operan en la banda de 28 GHz. Para satisfacer esta demanda el diseno circuitos integrados monoliticos de microondas (MMIC) es de gran interes ya que poseen ventajas en cuanto a miniaturizacion,. gran repetitibidad, bajo coste en grandes producciones y mayor fiabilidad debido al reducido numero de interconexiones. 2. DISENO Se ha realizado el diseno de dos amplificadores en la banda Ka, uno de ellos de tres etapas y el otro de cuatro. Los modelos de pequena senal de los transistores utilizados para realizar el diseno estan proporcionados por la fundicion para cada polarizacion. En ambos disenos los transistores son de tipo deplexion y tamano 6x15 µm. Se ha escogido la menor anchura de dedo permitida por la fundicion para disminuir la resistencia de puerta y asi minimizar el ruido. Por otro lado con este tamano, a traves de la realimentacion inductiva en fuente, permite aproximar la impedancia optima de ruido a la impedancia de adaptacion conjugada. En la figura 1 se observa un esquema de la topologia del amplificador de cuatro etapas. Para el amplificador de tres etapas se utilizo una topologia similar al representado en la figura1. Figura 1 . Esquematico del Amplificador MMIC de 4 etapas La primera etapa en los dos disenos lleva realimentacion inductiva en la fuente [1] con el fin de obtener bajo ruido con una ganancia y perdidas de conversion razonables. Las otras dos etapas en el caso del amplificador de tres etapas y las tres etapas finales en el amplificador de cuatro etapas llevan realimentacion resistiva paralela [2,3] con el objetivo de obtener una ganancia constante en todo el rango de funcionamiento al compensar la caida natural en ganancia de un transistor con la frecuencia. Esta realimentacion paralela tiene un impacto minimo en la figura de ruido y asegura estabilidad incondicional a todo el amplificador. La figura 2 muestra una fotografia de cada uno de los amplificadores monoliticos. Ambos circuitos tienen el mismo tamano e igual a 3x1 mm

Nuevo modelo de gran-señal para transistores mesfet de microondas incluyendo efectos opticos

Abstract: This paper is the result of our research on large signal dynamic behavior (Pulsed I/V curves) of GaAs device, in the overall I/V plane, when the incident optical input power is changed. A complete bias and optical power dependent large signal model for a MESFET is determined from experimental Sparameters, DC and pulsed measurements. All derivatives of the model shown here are continuous for a realistic description of circuit distortion and intermodulation. The dependencies of circuit elements with optical illumination and the quiescent operating point are evaluated, and a comparison between theoretical and measured results over optical power and bias ranges is shown. Experimental results show a very good agreement with the theoretical analysis. 1. INTRODUCCION

Nuevo modelo de capacidad de puerta para transistores MESFET de microondas incluyendo efectos ópticos

Abstract: A new set of pseudo -empirical equations are presented in order to simulate the optical and bias dependencies of GaAs MESFET junction capacitances, which is valid for the whole I-V plane. The variations induced in the small signal equivalent circuit by the optical illumination are extracted from on-wafer scattering parameter measurements. New linear and quasilogarithmic variations versus the incident optical power are shown for gate-to-drain and gate-to-source (Cgd and Cgs) capacitances. Furthermore, experimental results are in very good agreement with the simulated values for a wide range of optical power and bias conditions.