Sharif Digital Repository

Dental professionals are in a unique position to promote smoking cessation among their patients. We evaluated the effects of a brief counselling intervention by a dentist on patients' attitude towards the role of dentists in tobacco cessation programmes. In a semi-experimental study in Tehran, Islamic Republic of Iran, 70 eligible smokers were selected and randomly assigned to intervention and control groups. The initial attitudes of the patients regarding tobacco cessation counselling services provided by the dentist were determined using a validated questionnaire. The intervention group received a brief chair-side counselling by a dentist based on the 5 A's approach, while no intervention... 

Boost converter operating in critical conduction mode is widely used in low-power power factor corrector because of its simplicity and low switching losses. The switching loss due to parasitic capacitor discharge at the on-time instant can also be reduced by a valley switching technique. In this paper, we introduce a new driver topology for the high-side switch in a synchronous boost converter operating in the critical conduction mode to obtain full zero-voltage switching. Using the proposed high-side driver topology, the conventional control circuit is sufficient to control the low-side switch, and no additional control circuit is required to adjust the timing of the switches. Finally, the... 

A very low-power RF front-end based on a new current reuse QLMV cell (Quadrature VCO-LNA-Mixer) is proposed for GPS applications. The front-end, designed in 0.18μm CMOS technology, provides improved performance characteristics while consuming only 1 mA current. Simulation results are presented and compared with recently published works in the field  

The unique properties of modified Hermite pulses is utilized to develop a novel pulse technique for Ultra Wideband (UWB) communications. The proposed method increases the bandwidth of the pulse up to 10 GHz and overcomes the coexistence problem of UWB and vulnerable narrowband systems through suppressing narrowband interference. Consequently it improves the range of UWB communications by increasing the power, without disturbing the narrowband systems. The pulse technique is implemented in high frequency pulse generation circuits and could be fully integrated in BiCMOS process. The nulls of the frequency response are tuned to be located in a definite narrowband system with the number of the... 

In this paper we introduce a new low phase noise cascode Cross-coupled oscillator by use of the general topology of Cross-coupled oscillator and cascode amplifier. By simulation a comparison between the conventional Cross-coupled oscillator and the new cascode Cross-coupled oscillator is also presented, which shows that the latter improves the phase noise by 2dB under the same conditions. The figure of merit (FOM) of -186.4 dBc/Hz is achieved for the new oscillator by simulation  

The Class-E power amplifier has been widely studied and formulated in the literature. Although the majority of reported inductive coupling wireless power transfer (WPT) systems use a class-E power amplifier for driving the primary coil, still there is a lack of a comprehensive study on class-E circuit dedicated to WPT, providing a set of closed form design equations for proper class-E operation. This paper presents the required design equations needed to design a 'true' class-E circuit for WPT applications. Equations for the series-tuned secondary coil WPT system are presented, as well as two different design procedures for the parallel-tuned secondary coil. The derived equations have been... 

Self-oscillating converters operating in the critical conduction mode are popular in low power applications because of their simplicity and low cost. However, these converters are not suited for Power Factor Correction (PFC) because the peak switch current is controlled to regulate the output voltage and does not follow the shape of the line voltage waveform. A new control circuit implementation is proposed for a self-oscillating boost converter to achieve power factor correction. A full featured design example is provided which can be simplified for use in various cost sensitive applications such as electronic lighting, etc. This wide input voltage range self-oscillating PFC prototype... 

In this paper, the effect of imperfections on the behavior of N-path filters is investigated. Exact mathematical derivations are presented which describe the effect of clock skew and finite fall/rise time on the impedance transformation behavior of N-path filters. In the ideal case, the N-path filter is supposed to provide a short-circuit to the ground for undesired frequency contents and an open-circuit for the desired signal so that it lies within the passband of the filter. It is shown that clock skew and finite clock fall/rise time result in a non-zero impedance for frequency contents other than the clock frequency and a smaller impedance for the desired voltage. In a real circuit with... 

A systematic method to design high power and high efficiency mm-wave fundamental oscillators is presented. By using a linear time variant method, we first obtain the optimum conditions and show that these conditions can be significantly different for high power and high efficiency fundamental oscillation. Next, we propose a modified multistage ring oscillator with interstage passive networks to exploit the full capacity of the transistors in terms of output power or efficiency. Analytical expressions are also derived to determine the value of passive elements used in the oscillator. To verify the validity of the method, a 77-GHz two-stage (differential) VCO is designed in a 65-nm CMOS... 

A new low-power current reuse topology is proposed for the GPS receiver's RF front-end that combines the higher conversion gain and suppressed noise figure characteristics of cascade structures with the low power consumption of stacked architectures. The presented circuit, called 1.5-stage LMV cell, consists of LNA, Mixer and VCO (LMV) in such a formation that boosts LNA gain and suppresses mixer's noise figure by cascading the two stages while reusing their currents in the two stacked quadrature VCOs and placing the mixer's upper tree switches at the vicinity of on-off regions. The circuit is designed and its layout is generated in TSMC 0.18μm CMOS technology. Post-layout simulations using... 

Taking account of uncertainty in multicriteria decision making problems is crucial due to the fact that depending on how it is done, ranking of alternatives can be completely different. This paper utilizes linguistic values to evaluate the performance of qualitative criteria and proposes using appropriate shapes of fuzzy numbers to evaluate the performance of quantitative criteria for each problem with respect to its particular conditions. In addition, a process to determine the weights of criteria using fuzzy numbers, which considers their competition to gain greater weights and their influence on each other is described. A new fuzzy methodology is proposed to solve such a problem that... 

An alternative approach to analysis, design and implementation of injection-locked quadrature oscillators is proposed in this paper. A novel technique is presented which allows the effects of the mismatches due to imbalances in the I/Q paths in transceivers (TRX) to be mitigated, and hence the orthogonality of the these vectors be maintained. This technique alleviates the effects of imbalances in a transceiver between I/Q paths, which would otherwise pose many threats to the performance of the system, namely image rejection ratio (IRR) degradation, gain reduction in mixers, desensitization of the RX, and ect. As a design example, a CMOS quadrature oscillator (QOSC) at the frequency of 3.5GHz... 

A systematic approach to I/Q mismatch calibration in image-reject receivers is presented in this paper. A new error detection algorithm is proposed, which automatically calibrates for phase and gain mismatches limiting the performance of image-reject receivers. A dual-loop feedback is employed which looks for the minimum phase/gain error using a 2-dimensional analog-based search algorithm and then finds the minimum value for the error. An experimental CMOS prototype RF front-end for cognitive radio applications operating at 400-800 MHz is proposed and simulated in the 0.18 μm CMOS technology, achieving an image rejection ratio (IRR) better than 55-dB in post-layout simulation. The... 

Two important drawbacks of parallel coupled LC quadrature oscillators (P-QOSC) which have not heretofore been addressed thoroughly in the literature are obviated simultaneously in this paper. The first, has to do with the inevitable off-tune operation of the tank which results in quality factor (Q) degradation, and hence, phase noise deterioration. The other, stems from process, voltage, and temperature (PVT) variations which exacerbate quadrature accuracy. Here, a feedback loop is presented which generates a control signal by mixing the quadrature outputs and tunes the injection strength in the coupled oscillators autonomously. A complex coupling factor is implemented which compensates the... 

A new phase noise calculation method is proposed in which noise sources are modeled with single tone sources. It uses a nonlinear frequency-domain analysis to calculate total gain from noise sources to the output phase noise. This single tone (ST) simulation directly calculates noise frequency contributions and is much faster than Hajimiri's impulse sensitivity function (ISF) method. A quadrature VCO has been implemented in TSMC 0.18-μm CMOS and the predicted phase noise matches measurement. © 2009 IEEE  

This paper presents a new architectural solution to address the critical challenge of self-interference (SI) in radar systems sharing a Tx/Rx antenna. Here, the SI problem, often leading to receiver nonlinearity or saturation, is significantly mitigated using a new active circulator integrated with a quadrature-fed cross-dipole antenna within the introduced radar transceiver architecture. This configuration results in circular-polarized radiation of the transmitting signal, segregating the desired (echo) and undesired (SI) signals into differential and common-mode inputs, and highly attenuating the SI. As a proof of concept, the proposed SI cancellation configuration is designed for... 

[No abstract available]  

A new Ultra Wideband (UWB) pulse shape is proposed to mitigate coexistence issues of IEEE802.11.a WLAN and Impulse Radio UWB (IR-UWB) systems. The proposed method is applicable to the reduction of any given narrowband (NB) interference into UWB systems. This pulse shape is based on frequency up-converting of first derivative of Gaussian pulse which has an adjustable null in Power Spectral Density (PSD) depending on up-converting frequency. Both analytical and simulation results with an adaptive receiver show that an UWB system with interference from a WLAN has noticeable improved performance when using the proposed pulse in comparison with using conventional modulated Gaussian pulse  

The conventional theory of super regenerative systems (SRS) has been divided into distinct modes of operation and limiting assumptions. These assumptions make the analysis of these systems inaccurate for wide bandwidth applications. In this paper, a novel theory based on the analysis of time varying systems using Magnus expansion is proposed which unifies all modes of operation and formulates the system response with high accuracy for a wide range of practical applications. Therefore, the theory can be used for the design of systems with wider bandwidth and higher data rates. Using the proposed theory, it is possible to analytically describe the effects of the parasitic elements and inter... 

Exact spread-spectrum code tracking in the presence of multipath is an important issue in distance and time measurement systems. Different tracking algorithms based on feedback, feedforward or a combination of them reduce multipath effects, however, the accuracy of the tracking in presence of short-delay multipath signals is still a problem. In this paper, we consider feedback delay lock loops (DLL) and gating function schemes that have shown better performance with lower complexity under multipath. We develop a shot-noise process model for the control signal of a DLL in the presence of multipath signals and determine the range of tracking errors they cause. Then, we propose a method based...