Phase detector | EPFL Graph Search

A phase detector or phase comparator is a frequency mixer, analog multiplier or logic circuit that generates a signal which represents the difference in phase between two signal inputs. The phase detector is an essential element of the phase-locked loop (PLL). Detecting phase difference is important in other applications, such as motor control, radar and telecommunication systems, servo mechanisms, and demodulators. Types Phase detectors for phase-locked loop circuits may be classified in two types. A Type I detector is designed to be driven by analog signals or square-wave digital signals and produces an output pulse at the difference frequency. The Type I detector always produces an output waveform, which must be filtered to control the phase-locked loop voltage-controlled oscillator (VCO). A type II detector is sensitive only to the relative timing of the edges of the input and reference pulses and produces a constant output proportional to phase difference when both s

Low power frequency synthesizer for mobile communications systems

Imre Kovacs

A novel frequency synthesizer with a strong emphasis on low-power consumption (2mW) was developed for this thesis. A BAW-resonator was used for the design of the high-frequency oscillator. The BAW's high Q-Factor ensured a minimal power consumption, while providing outstanding phase noise performance. This type of frequency synthesizer can be implemented in practically every mobile wireless system standard, which is relying on batteries as the power supply, such as Bluetooth, Zigbee and others. For this work, a Bluetooth-compatible standard was taken in order to derive the system specifications. The frequency synthesizer then was designed and implemented in a 180nm CMOS process. The approach of the "Sliding-IF" architecture was chosen and modified in order to take full advantage on the BAW oscillator. Therefore a two-stage frequency translation of the signal was necessary, similar to the super-heterodyne transceiver topology. The channel selection and the frequency error correction is done at the second stage, since the BAW-based oscillator does practically not provide any frequency tuning. For this, a Delta-Sigma-Modulator based Fractional-N PLL was developed. A system supply voltage of 1.2V was chosen in order to keep power consumption as low as possible. This supply voltage can also be easily supplied by AA or AAA-batteries and a low-voltage regulator. The most important technique to reduce overall power consumption was to reduce the high-frequency requirements to the system blocks. This was done by modifying the "Sliding-IF" architecture and by the use of the BAW resonator. The minimization of the power consumption required careful choice and design of each of the system blocks. For this, several approaches were analyzed, especially the topology of each block and its optimization were important. A special emphasis on the analysis, design and discussion was also made on the noise, and especially the phase noise. A ring oscillator, a LC-VCO and a BAW-oscillator were implemented and measured in order to validate the theory and the simulation results. The complete frequency synthesizer with an Automatic Amplitude Control, Frequency Dividers, Mixer, Charge-Pump, Phase-Frequency Detector and a Delta-Sigma-Modulator was designed and implemented. This thesis was elaborated in the frame of the MiNAMI and MiMOSA projects of the European research programme (FP6).

EPFL2009

Graphene-based Field-effect Transistors

Adarsh Singh Sagar

With transistors set to reach their smallest possible size in the next decade, the silicon chip is likely to change dramatically, or be replaced entirely. The transistor industry's path which has been largely shaped by Gordon Moore's famous prediction that the number of transistors on a silicon chip would double approximately every eighteen months, predicts a size of transistor which silicon technology cannot sustain, thereby ushering in a post-silicon age in semiconductors soon. In this scenario, graphene-derived nanomaterials are emerging as promising candidates for post-silicon electronics devices, with potential applications as atomically thin transistors and other nanoelectronic devices which incorporate quantum size effects. However, such claims still require a few important issues to be addressed first . This thesis focuses on demonstrating and studying field effect behaviour in graphene- and graphite-based devices. It describes the differences between the two types of graphene bilayers and the effect of their stacking order when placed in an electric field. The differences are studied using Scanning Photocurrent Microscopy, leading to the conclusion that the bottom layer in a misoriented bilayer effectively screens the charge carrier modulation when used in a back-gated FET configuration. A polymer electrolyte gate was employed on top to ultilise the enhanced carrier mobility within the top layer. The study is extended from bilayer graphene to multilayer graphene (graphite) while addressing a possibility of fabricating a field effect transistor on such a material. The thesis comments on the differences between each of these and their prospects in future applications. While emphasizing the effect of the substrate in such FETs, an intrinsic gain in a graphene-based FET of over one is shown at room temperature. The importance of both these aspects in the devices is also elucidated. Furthermore, the misoriented bilayer transistors were incorporated into phase-shift detectors, to exhibit their functioning in logical circuits. On the technical side, a novel method for fabricating graphene-based transistors on a lab-scale has been demonstrated which uses fluorescence quenching to distinguish the number of layers in a graphene stack.

EPFL2011

ECG periodic components as a promising tool for complexity assessment during stepwise ablation of atrial fibrillation

Andréa Buttu, Etienne Pruvot, Jérôme Sébastien Van Zaen, Jean-Marc Vesin

Introduction: Stepwise radiofrequency catheter ablation (step-CA) has become a treatment of choice for the restoration of sinus rhythm (SR) in patients (pts) with long-standing persistent atrial fibrillation (pers-AF). Its success rate appears limited as the amount of ablation to achieve long term SR is unknown. Recently, intracardiac organization indices (OI) of AF have been used to track the efficiency of step-CA, with limited success. Our study is aimed at developing new OIs based on the relationships between harmonic components of atrial activity from the surface ECG as a global assessment of AF complexity and organization during step-CA. Methods: 3 pts with pers-AF (age 62, AF duration 17 months) underwent a step-CA. An adaptive tracking algorithm was developed for estimating the instantaneous frequency of atrial activity on chest lead V1 (after QRST subtraction) and for extracting its fundamental and harmonic components. An adaptive organization index (AOI) was computed as the ratio between the power of the extracted components and the total power of the signal to evaluate the temporal evolution of AF oscillations. The variance of the phase difference (PD) between the fundamental and harmonic components was used for measuring AF regularity. Results: Step-CA terminated 2/3 pers-AF into flutter. Importantly, in the 2 terminated pts, the AOI did not show any significant change during the step-CA (from pre-ablation to CFAE), while the PD showed a gradual reduction suggestive of increased coupling between the fundamental and the 1st harmonic. See figure. Conclusions: The PD and the AOI as measurements of complexity from the surface ECG appear as promising methods for tracking the effect of step-CA on global AF organization. This, however, needs to be validated on a larger population.

2011