Christian Rumelhard

A high-efficiency and low-phase-noise 38-GHz pHEMT MMIC tripler

Frequency translation circuits are key elements in communication systems. This paper presents a frequency tripler for 38-GHz short-range communication systems, designed using a pseudomorphic high electron-mobility field-effect transistor (pHEMT) technology. The successful first iteration monolithic microwave integrated circuit achieved a state-of-the-art output power of 3.1 dBm and a minimum conversion loss of 3.4 dB. The multiplier exhibits a conversion efficiency of 11% and average phase noise degradation at 10 and 100 kHz offset frequency from carrier of 9/spl plusmn/1 dB. Through a comprehensive study of the frequency multiplier, we demonstrate the optimum performance achieved under a class B mode of operation. To our knowledge, this is the first reported Ka-band single-stage frequency tripler based on pHEMT technology that has been fully characterized for phase noise degradation.

A compact, monolithic microwave demodulator-modulator for 64-QAM digital radio links

The design, fabrication and performance of a monolithic microwave direct modulation modulator-demodulator are presented. The subsystem is designed to work in a 64-QAM digital radio link. At this level of modulation, it is necessary to have some possibilities of phase and amplitude trimming by external voltages to achieve sufficient accuracy. The circuit includes elementary functions such as quadrature and in-phase splitters, and circuits giving the possibility to adjust phases and amplitudes for 64 QAM and higher level modulation. The design is such that the same chip can be used either as a direct demodulator or as a modulator. This complex circuit of small dimensions (2.7 mm*3.65 mm) exhibits good demodulation and modulation performances. The overall performances of this monolithic circuit are achieved without degrading the DC yield. >

Optimization of InP-InGaAs HPT gain: design of an opto-microwave monolithic amplifier

We have designed an opto-microwave monolithic amplifier with emphasis on the definition of the opto-microwave power gain. First, we present physical simulations of an InP-InGaAs heterostructure phototransistor (HPT), which enable the structural analysis of the composition and behavior of the phototransistor. From these simulations and from both electrical and optical measurements, we next established a large-signal model, which adds photoelectric effect to an HBT model. Small-signal opto-microwave S-parameters of the HPT are first defined and then related to the small-signal opto-microwave power gain of the phototransistor. Relations are given to enable optimum loads on the base and collector ports to be found so that the opto-microwave gain can be optimized. An opto-microwave amplifier is then designed, realized, and measured with a setup based on the beating of two lasers.

Simulation of microwave optical links and proof of noise figure lower than electrical losses

The operation of a microwave photonic link is thoroughly investigated both theoretically and experimentally. To this aim, we have developed a simulation tool based on an accurate physical model embedded in a radio frequency (RF) chain simulator. The theoretical predictions are tested on an intensity modulation-direct detection (IMDD) link we have specifically developed to this purpose. Our simulation tool takes into account both optical and electrical characteristics of the link components including the laser dynamics and impedance matching networks. It thus enables an accurate understanding of the different physical and electrical phenomena governing the links performances even under unusual operation conditions. Specifically, we were able to isolate an unusual behavior and to confirm it experimentally. It is thereby clear that the noise figure of a microwave optical link can be lower than the electrical losses, such as a mismatched output passive electrical network. This state is reached when the optical losses are high enough and when the links output impedance is mismatched, too.

Opto-microwave experimental mapping of SiGe/Si phototransistors at 850 nm

This paper presents measurement results providing the mapping of the opto-microwave transfer function performed on an SiGe microwave heterojunction phototransistor (HPT). This measurements will be used to extract a guideline for designing phototransistors. A mapping of the HPTs gain in low frequency helps to estimate the shape of the optical beam used for the measurement. The study also focuses on the cutoff frequency mapping of the device in phototransistor mode. Finally, these results are used to determine the general optimization rules in the SiGe HPTs design.

GaAs monocycle pulse generator for UWB applications

This paper reports the design and test of a wavelet generator circuit which provides ultra short monocycle pulses of about 300 ps width alternately in phase and out of phase. This generator circuit is based on the representation of the pulse as a mathematical function which is a combination of four hyperbolic tangents. The final circuit of the generator was designed and realized on a monolithic microwave integrated circuit (MMIC) GaAs technology based on a pseudomorphic heterojunction FET (PHEMT) having a gate length of 0.25 mum (PH25 of UMS foundry).

Monolithic Microwave Integrated Circuits for Telecommunications

In a first part, a review of basic monolithic circuits which are used in telecommunications under 20 GHz is done : low noise amplifiers, voltage controlled oscillators, phase shifters and mainly the mixers which are specific to this application. Then, some examples of circuits working at higher frequencies are given. Starting from these basic circuits complete monolithic subsystems are now in development. Representative examples are described.

Coupling and Impedance Between Line and Ground Electrodes on GaAs ; Implications for MMIC Design

Addressing the need for quantitative design rules in C.A.D. of microwave GaAs i.c.s, we describe the evaluation of microwave coupling and impedance for various systems of conductors on GaAs substrates. In particular, the coupling between two parallel microstrip lines has been calculated as a function of the presence of an intermediate screening electrode. Measurements. of the effect support the calculated data, and confirm a substantially reduced coupling across the electrode when grounded. The impedance of a line on a back-metallised substrate, with a parallel coplanar ground electrode has also been determined for a range of line geometries.

A 40 Gbps electro-absorption modulator integrated laser modeling method for optical transmitter in ultra-wide band radio-over-fiber systems

The great interest of optical fiber links in communicating systems especially in ultra-wide band (UWB) communications has grown up in the last decade and requires co-simulation for mixed circuits design exploiting both optical and microwave domains. In this paper, we report an original modeling method of an electro-absorption modulator associated with a distributed-feedback laser to simulate an optical transmitter of an UWB over fiber system. Large signal optoelectronic device models can be developed and implemented in a high-frequency simulator, such as advanced design system-Ptolemy to analyze the performances of fiber radio links and study the impact of the transmitter characteristics. This specific simulation way, taking into account precisely electrical characteristics of both electrical and optical circuits, links two different frequency domains by coupling electrical and optical modules in the same system simulator. Therefore, a complete simulation of an UWB multi-band orthogonal frequency division multiplexing signal transmission over fiber with an external modulator is investigated.

A compact, monolithic radiofrequency demodulator-modulator for 64-QAM digital radio links

The design, fabrication, and performance of a GaAs monolithic radiofrequency demodulator with phase and amplitude trimming in the quadrature coupler and balanced mixers in the 5.9-8.5 GHz range is described. This circuit includes amplitude and phase trimming circuits, two single balanced mixers, couplers, and a quadrature phase comparator. The design is such that the same chip can be used either as a direct 64 QAM (quadrature amplitude modulation) demodulator or a modulator. The small chip size is 2.7 mm*3.65 mm.<<ETX>>