High-frequency equivalent circuit of GaAs FET's for large-signal applications

The application of GaAs field effect transistors in digital circuits requires a valid description by an equivalent circuit at all possible gate and drain bias voltages for all frequencies from DC up to the gigahertz range. An equivalent circuit is presented which takes into account the gate current of positively biased transistors as well as the symmetrical nature of the devices at low drain voltages. A fast method of determining the elements of the equivalent circuit at all bias points without frequency limitations is presented. Direct computation from analytical expressions, without iteration, allows this parameter extraction procedure to be used for real-time on-wafer parameter extraction. Large-signal calculations are possible by inserting the voltage dependences evaluation for the elements into suitable simulation programs, such as SPICE

Frequency dependent CV measurements of GaAs/AlGaAs heterostructures

A procedure is described to determine the carrier density profile in the channel of a FET by evaluating S-parameters measured over a broad frequency range. Applying this method to GaAs/AlGaAs heterostructures, a frequency dispersion of the gate capacitance has been found, which is attributed to a parasitic conducting channel

Design and Development of an Electrolarynx With Variable Frequency and Integrated Bluetooth Air Interface

Eine Elektrolarynx ist eine Sprechhilfe für laryngektomierte und tracheotomierte Patienten, die beispielsweise durch Kehlkopfkrebs ihre Stimmbänder ganz oder teilweise verloren haben. Herkömmliche Geräte arbeiten mit einer monotonen fest eingestellten Frequenz, die nur von einem Arzt neu eingestellt werden kann. Die Stimme klingt daher sehr „roboterhaft“, da es dem Patient nicht möglich ist, mit seiner Stimmfrequenz dem Satzbau zu folgen. Im Rahmen einer Diplomarbeit wurden neue Konzepte und Methoden entwickelt die Sprachqualität, insbesondere die Intonation zu verbessern. Mit dem Einsatz eines resistiven Folien-Drucksensors (FSR) in Verbindung mit einer Mikrocontrollerschaltung und einer Bluetooth-Kommunikationseinheit wurde ein Prototyp aufgebaut, der im Bereich der elektronischen Sprechhilfen einen großen Vorschritt darstellt. Neben den neuen Möglichkeiten der Sprachgestaltung ist das Gerät um ein vielfaches komfortabler auf den jeweiligen Patienten einstellbar und kann darüber hinaus auch vom Patienten selbst konfiguriert werden

A monolithic HEMT-amplifier with feedback in coplanar waveguide technology

A monolithic integrated wide-band amplifier is presented, which consists of two 0.3 μm HEMT-stages in GaAs/GaAlAs-Technology. The main signal path consists of a coplanar waveguide, which interfaces conveniently to the HEMT-cells. A feedback circuit with R, L and C connects gate and drain. To close the feedback loop small scale microstrip lines were combined with CPW /1, 2, 4/. Matching is done with a LC circuit at the gate and a combination of transmission line and capacitor at the drain. In addition there are some other passive elements for biasing, which reduce external components to a minimum. All element models were checked with measured data and placed into a CAD-library for easy use in the design process

Novel push-pull chromophores to prepare electro-optic modulators

In recent years, a large number of push-pull organic molecules have been proposed as promising candidates for electronic and optical applications. Generally, the main effort has been focused on the design of chromophores with large first hyperpolarizability values (β); this would result in a wide variety of nonlinear optical (NLO) applications, such as modulators.[1,2] In this work, we report an experimental and theoretical investigation of the NLO properties of novel push-pull systems derived from the dicyanomethylene-4H-chromene (DCM) group. Particular attention will be paid to better understand the molecular and electronic properties of these systems by using vibrational spectroscopic techniques and electrochemistry. Furthermore, these materials have been tested in a silicon-organic hybrid modulator based on an integrated dual-mode interferometer.[3]Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Comprehensive Life Cycle Support for Access Rules in Information Systems: The CEOSIS Project

The definition and management of access rules (e.g., to control access to business documents and business functions) is a fundamental task in any enterprise information system (EIS). While there exists considerable work on how to specify and represent access rules, only little research has been spent on access rule changes. Examples include the evolution of organizational models with need for subsequent adaptation of related access rules as well as direct access rule modifications (e.g., to state a previously defined rule more precisely). This paper presents a comprehensive change framework for the controlled evolution of role-based access rules in EIS. First, we consider changes of organizational models and elaborate how they affect existing access rules. Second, we define change operations which enable direct adaptations of access rules. In the latter context, we define the formal semantics of access rule changes based on operator trees. Particularly, this enables their unambiguous application; i.e., we can precisely determine which effects are caused by respective rule changes. This is important, for example, to be able to efficiently and correctly adapt user worklists in process-aware information systems. Altogether this paper contributes to comprehensive life cycle support for access rules in (adaptive) EIS

Integrated laser-diode voltage driver for 20-Gb/s optical systems using 0.3- μm gate length quantum-well HEMT's

An integrated laser-diode voltage driver (LDVD) making use of enhancement/depletion AlGaAs-GaAs quantum-well high electron mobility transistors (QW HEMTs) with gate lengths of 0.3 μm has been developed. Its large signal bandwidth is 12 GHz. Eye diagrams of the output signal at bit rates up to 8 Gb/s show an opening similar to that of the input signal. Supporting material is given indicating that the LDVD might operate at bit rates up to 20 Gb/s. The maximum output current is over 90 mA; the maximum modulation voltage of 800 mV corresponds to 40-mA modulation current for a laser diode with 20-Ω dynamic resistance. The power consumption is less than 500 mW

8.2 GHz bandwidth monolithic integrated optoelectronic receiver using MSM photodiode and 0.5 μm recessed-gate AlGaAs/GaAs HEMTs

An 8.2 GHz bandwidth monolithic optoelectronic receiver consisting of an MSM photodiode, a transimpedance amplifier, and a 50 Omega output buffer has been fabricated using an enhancement/depletion 0.5 μm recessed-gate AlGaAs/GaAs HEMT process. Successful operation at data rates up to 10 Gbit/s has been demonstrated

7.5 Gb/s monolithically integrated clock recovery using PLL and 0.3 μM gate length quantum well HEMTs

A monolithically integrated clock recovery (CR) circuit making use of the phase-locked loop (PLL) circuit technique and enhancement/depletion AlGaAs/GaAs quantum well high electron mobility transistors (QW-HEMTs) with gate lengths of 0.3 μm has been realized. A novel preprocessing circuit was used. In the PLL a fully-balanced varactorless VCO has been introduced. The VCO has a centre oscillating frequency of about 7.5 GHz and a tuning range greater than 500 MHz. A satisfactory clock signal has been obtained at the bit rate of about 7.5 Gb/s. The power consumption is less than 200 mW at the supply voltage of -5 V