Ana Rusu

Reconfigurable ADCs enable smart radios for 4G wireless connectivity

A reconfigurable ADC based on a 2-2 modified cascaded SigmaDelta modulator designed for a GSM/WCDMA/WLAN/WiMAX zero-IF receiver has been presented. Employing the second-order feedforward SigmaDelta modulator in a 2-2 modified cascaded configuration, a high linearity over 100 kHz/2 MHz/10 MHz signal bandwidth is achieved. The P-DWA technique is applied in the first feedback 4-b DAC to eliminate the spurious tones associated with the multibit DAC nonlinearity in the WLAN/WiMAX modes

A Comprehensive Graphene FET Model for Circuit Design

During the last years, graphene-based field-effect transistors (GFETs) have shown outstanding RF performance; therefore, they have attracted considerable attention from the electronic devices and circuits communities. At the same time, analytical models that predict the electrical characteristics of GFETs have evolved rapidly. These models, however, have a complexity level that can only be handled with the help of a circuit simulator. On the other hand, analog circuit designers require simple models that enable them to carry out fast hand calculations, i.e., to create circuits using small-signal hybrid - π models, calculate figures of merit, estimate gains, pole-zero positions, and so on. This paper presents a comprehensive GFET model that is simple enough for being used in hand calculations during circuit design and at the same time, it is accurate enough to capture the electrical characteristics of the devices in the operating regions of interest. Closed analytical expressions are provided for the drain current ID, small-signal transconductance gain gm, output resistance ro, and parasitic capacitances Cgs and Cgd. In addition, figures of merit, such as intrinsic voltage gain AV, transconductance efficiency gm/ID, and transit frequency fT are presented. The proposed model has been compared to a complete analytical model and also to measured data available in current literature. The results show that the proposed model follows closely to both the complete analytical model and the measured data; therefore, it can be successfully applied in the design of GFET analog circuits.

Spin-Torque and Spin-Hall Nano-Oscillators

This paper reviews the state of the art in spin-torque and spin-Hall-effect-driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.

A Low-Power CT Incremental 3rd Order /spl Sigma//spl Delta/ ADC for Biosensor Applications

This paper proposes a 3rd order single-loop continuous-time incremental sigma-delta analogue-to-digital converter (ADC) for time-multiplexed signals. Incremental sigma-delta modulation is used to address medium to high resolution requirements of multi-channel applications, while a 3rd order continuous-time implementation is investigated as an alternative for low-power solutions. A prototype of the proposed modulator, running at 320 kHz, has been fabricated in a 0.15-μm CMOS technology, while the synchronization circuitry to allow incremental operation was built on-board. Measurement results show that the ADC achieves 65.3 dB peak SNR, 64 dB peak SNDR and 68.2 dB dynamic range over a 2 kHz bandwidth. The modulators power dissipation is 96 μW from a 1.6 V power supply. This translates into the best figure-of-merit when compared to recently published continuous-time alternatives, while being competitive with respect to state-of-the-art discrete-time counterparts.

A Monolithic, 500 °C Operational Amplifier in 4H-SiC Bipolar Technology

A monolithic bipolar operational amplifier (opamp) fabricated in 4H-SiC technology is presented. The opamp has been used in an inverting negative feedback amplifier configuration. Wide temperature operation of the amplifier is demonstrated from 25°C to 500°C. The measured closed loop gain is around 40 dB for all temperatures whereas the 3 dB bandwidth increases from 270 kHz at 25°C to 410 kHz at 500°C. The opamp achieves 1.46 V/μs slew rate and 0.25% total harmonic distortion. This is the first report on high temperature operation of a fully integrated SiC bipolar opamp which demonstrates the feasibility of this technology for high temperature analog integrated circuits.

RF Performance Projections of Graphene FETs vs. Silicon MOSFETs

A graphene field-effect-transistor (GFET) model calibrated with extracted device parameters and a commercial 65 nm silicon MOSFET model are compared with respect to their radio frequency behavior. ...

Secure and Privacy-Preserving Smartphone-Based Traffic Information Systems

Increasing smartphone penetration, combined with the wide coverage of cellular infrastructures, renders smartphone-based traffic information systems (TISs) an attractive option. The main purpose of such systems is to alleviate traffic congestion that exists in every major city. Nevertheless, to reap the benefits of smartphone-based TISs, we need to ensure their security and privacy and their effectiveness (e.g., accuracy). This is the motivation of this paper: We leverage state-of-the-art cryptographic schemes and readily available telecommunication infrastructure. We present a comprehensive solution for smartphone-based traffic estimation that is proven to be secure and privacy preserving. We provide a full-blown implementation on actual smartphones, along with an extensive assessment of its accuracy and efficiency. Our results confirm that smartphone-based TISs can offer accurate traffic state estimation while being secure and privacy preserving.

500 °C Bipolar SiC Linear Voltage Regulator

In this paper, we demonstrate a fully integrated linear voltage regulator in silicon carbide NPN bipolar transistor technology, operational from 25°C up to 500°C. For 15-mA load current, this regulator provides a stable output voltage with <;2% variation in the temperature range 25°C-500°C. For both line and load regulations, degradation of 50% from 25°C to 300°C and improvement of 50% from 300°C to 500°C are observed. The transient response measurements of the regulator show robust behavior in the temperature range 25°C-500°C.

TACT: a multi-standard RF transceiver architecture comparison tool

One of the main challenges posed by 4G wireless communication systems is achieving flexible, programmable multi-standard radio transceivers with maximum hardware share amongst different standards at a minimum power consumption. Evaluating the feasibility and performance of different multi-standard/multi-band radio solutions at an early stage, i.e. system level, is key for succeeding in surmounting this challenge. This entails formulation of the transceiver budget for several RF architectures with different degrees of hardware reuse. This task is complicated by the fact that transceiver blocks can have different implementations that lead to different performances. The tools that are available for use at present have only budget analysis capabilities or address only one standard and/or transceiver architecture at a time. We believe that a new approach to this problem is necessary and propose a novel methodology for evaluating the performance of different multi-standard solutions. This paper introduces TACT, our multi-standard RF transceiver architecture comparison tool. It will help answering many of the challenges faced by designers when realizing a transceiver budget for multi-standard/multi-band radio transceivers.

Putting the "FLEX" in flexible mobile wireless radios - A wideband continuous-time baudpass sigma-delta ADC software radios

This article has provided a brief overview of the SigmaDelta ADC conversion technologies for SDRs. The wireless receiver challenges were identified, the ADC design considerations and SigmaDelta solutions were discussed, and a low-distortion CT BP SigmaDelta modulator architecture was presented. The article has shown that the proposed CT BP SigmaDelta modulator is suitable for implementing high-IF ADC, making possible the software radio in handhelds. The major challenges in implementing such a high-IF ADC are the power dissipation and the degree of configurability, programmability, and adaptability that can be achieved by applying digital tuning and adaptive calibration