The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Young-se Kwon - One of the best experts on this subject based on the ideXlab platform.
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Negative resistance circuit for monolithic resonators using gate-to-source resistive Feedback
Electronics Letters, 1998Co-Authors: Jong-soo Lee, Young-se KwonAbstract:A simple negative resistance circuit is developed for a resonator using a resistive Feedback between the gate and source terminal of a GaAs MESFET. The input conductance can be varied by a change of Feedback Resistor with small DC power consumption. The Q factor of the resonator is nearly 250 and shows a wide dynamic range.
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A novel active inductor and its application to inductance-controlled oscillator
IEEE Transactions on Microwave Theory and Techniques, 1997Co-Authors: Yong-ho Cho, Songcheol Hong, Young-se KwonAbstract:This paper describes a novel active inductor using a common-source cascode FET with an inductive Feedback. A compact lossy active inductor, which consists of a common-source FET and a Feedback Resistor, was used as the Feedback inductor to achieve high Q-factor and tunability, as well as reduce the chip size. The fabricated active inductor achieved more than 100 Q-factors with the maximum value of 3400 over the frequency range of 200 MHz, in the vicinity of 1.7 GHz. Inductance was tuned from 9.6 to 56 nH at 1.7 GHz by the variation of the Feedback resistance of the lossy active inductor. Using this active inductor (as a frequency-selective element in the resonator), a monolithic inductance-controlled FET oscillator was fabricated, which demonstrated an 18% frequency-tuning range from 1.73 to 2.07 GHz, with an output power range from -9.3 to -6.3 dBm.
Thomas Shenk - One of the best experts on this subject based on the ideXlab platform.
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An HIV Feedback-Resistor: Auto-Regulatory Circuit Deactivator and Noise Buffer
arXiv: Molecular Networks, 2007Co-Authors: Leor S. Weinberger, Thomas ShenkAbstract:Many viruses have the cunning ability to enter a hibernative or off state, termed latency or lysogeny. When in a latent state, the virus is unable to replicate, and its gene expression program is largely shut down. This facility for lying dormant typically ensures lifelong persistence of the virus in the host; it is also a particularly problematic obstacle in the treatment of HIV. For most viruses, the molecular regulation of entry into latency is not completely understood, but it is believed that viral gene expression must be deactivated in some way. In this study, we introduce a new regulatory motif, the Feedback Resistor, that enables a genetic circuit to shut off without the need for an active repressor molecule. We first show that many animal viruses might encode Feedback Resistors in their regulatory circuits. Then, by using a combination of mathematical theory and single-cell real-time imaging experiments, we show that a Feedback Resistor in the HIV Tat transcriptional circuit likely allows the HIV virus to enter into latency. We postulate that Feedback Resistors may give increased stability and control in the complex noisy signaling environment of the cell.
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An HIV Feedback Resistor: Auto-Regulatory Circuit Deactivator and Noise Buffer
PLoS biology, 2006Co-Authors: Leor S. Weinberger, Thomas ShenkAbstract:Animal viruses (e.g., lentiviruses and herpesviruses) use transcriptional positive Feedback (i.e., transactivation) to regulate their gene expression. But positive-Feedback circuits are inherently unstable when turned off, which presents a particular dilemma for latent viruses that lack transcriptional repressor motifs. Here we show that a dissipative Feedback Resistor, composed of enzymatic interconversion of the transactivator, converts transactivation circuits into excitable systems that generate transient pulses of expression, which decay to zero. We use HIV-1 as a model system and analyze single-cell expression kinetics to explore whether the HIV-1 transactivator of transcription (Tat) uses a Resistor to shut off transactivation. The Tat Feedback circuit was found to lack bi-stability and Tat self-cooperativity but exhibited a pulse of activity upon transactivation, all in agreement with the Feedback Resistor model. Guided by a mathematical model, biochemical and genetic perturbation of the suspected Tat Feedback Resistor altered the circuit's stability and reduced susceptibility to molecular noise, in agreement with model predictions. We propose that the Feedback Resistor is a necessary, but possibly not sufficient, condition for turning off noisy transactivation circuits lacking a repressor motif (e.g., HIV-1 Tat). Feedback Resistors may be a paradigm for examining other auto-regulatory circuits and may inform upon how viral latency is established, maintained, and broken.
T. Nakano - One of the best experts on this subject based on the ideXlab platform.
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steady state and dynamic analysis of a buck converter using a hysteretic pwm control
Power Electronics Specialists Conference, 2004Co-Authors: Jinbin Zhao, T. Sato, Takashi Nabeshima, T. NakanoAbstract:In this paper, steady state and dynamic analysis of a buck converter using a hysteretic PWM control scheme is presented. Since the proposed control scheme only uses a comparator with hysteresis and a Feedback Resistor, numbers of components in a control circuit are reduced. In addition, no error amplifier is used, thus the stability of the converter becomes excellent. The steady state and dynamic analysis of the proposed converter is performed and verified by experiments. We proved that the proposed control scheme has no phase lag and shows excellent transient response.
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A new PWM control scheme using a triangle waveform modulated by output voltage
Nineteenth Annual IEEE Applied Power Electronics Conference and Exposition 2004. APEC '04., 1Co-Authors: Jinbin Zhao, T. Sato, Takashi Nabeshima, T. NakanoAbstract:In this paper, a new PWM control scheme using a triangle waveform modulated by output voltage is presented. Since the proposed control scheme only uses a comparator with hysteresis and a Feedback Resistor, numbers of components in a control circuit are reduced. In addition, because no error amplifier is used, the stability of the converter becomes excellent. The steady-state analysis of the proposed converter is performed and verified by the experiments.
G. Berkowitz - One of the best experts on this subject based on the ideXlab platform.
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Variable bit-rate receiver for WDMA/WDM systems
IEEE Photonics Technology Letters, 1997Co-Authors: F. Tong, G. BerkowitzAbstract:We report the design, fabrication, and the characterization of a variable bit-rate receiver designed for wavelength-division multiplexing and wavelength division multiple access (WDM/WDMA) applications. The performances of these receivers can be optimized for bit-rates ranging from 300-1500 Mb/s. The tunability of the receiver bandwidth is achieved through adjusting the gate bias of a microFET used as an active Feedback Resistor in the transimpedance amplifier.
Horst Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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New methods for bandwidth enhancement of integrated high-sensitivity optical receivers
Photonic Materials Devices and Applications, 2005Co-Authors: C. Seidl, J. Knorr, R. Swoboda, Horst Dietrich, A. Nemecek, Horst ZimmermannAbstract:Optoelectronic integrated circuits (OEICs) offering high bandwidth and high sensitivity as well are needed for the pickups of optical storage systems of the next generation, such as Blu-Ray or HDDVD. High bandwidth is necessary to enable high data transfer rates between the disk and the processing device, and high sensitivity allows to operate at low optical power and to deal with the lower efficiency of the photodiodes for blue light. Two methods will be presented to increase the bandwidth of the OEIC while maintaining high sensitivity. The first approach reduces the parasitic capacitance by placing the Feedback Resistor in a low-doped region. By this way the parasitic capacitance of the Resistor is combined in series with the small depletion-layer capacitance of the low-doped region, which results in a drastically reduced effective capacitance. Using this method the 3dB-frequency of a standard one-stage transimpedance amplifier is increased by 55% from 67MHz to 104MHz. In the second approach the Feedback Resistor is replaced by a network that consists of two resistive voltage dividers that are coupled via a capacitor. Using such a capacitive-coupled voltage divider (CCVD) the Feedback path is split into a low- and a high-frequency path and the effective band-limiting RC-constant is reduced. A bandwidth of 378MHz could be achieved. With a measured transimpedance of 212kΩ this results in a GBW of 80.3THzΩ.
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Single-stage transimpedance amplifier for advanced DVD systems
Optoelectronic Integrated Circuits VI, 2004Co-Authors: Christoph Seidl, J. Knorr, R. Swoboda, Horst ZimmermannAbstract:For digital versatile disk (DVD) applications, amplifiers with high bandwidth and high sensitivity in the red spectral range are required. The presented optoelectronic integrated circuit (OEIC) achieves a bandwidth of 265MHz and a transimpedance of 210kΩ due to an advanced Feedback network. This is an improvement by a factor of 4 compared to the same amplifier with a simple Feedback Resistor.
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Investigation of optical interconnect receivers in standard micron and submicron MOS technology
Optical Engineering, 2003Co-Authors: T. Heide, Horst ZimmermannAbstract:Novel monolithic optical receivers in 0.8-mm standard MOS technology with non-return-to-zero data rates in excess of 531 Mbit/s at 850 nm are introduced. At 638 nm the data rates are above 622 Mbit/s. The innovative integrated double and pin photodiodes allowing this high speed without any modification in a CMOS process are described, and results for their quantum efficiency and for their transient response are presented. Furthermore, the improvement of the sensitivity of the photo- diodes and of the optoelectronic integrated circuits (OEICs) by an anti- reflection coating is discussed. The circuit topology of several OEICs is described. A transimpedance input stage with an active MOS Feedback Resistor is implemented. Analytical calculations for the bandwidth and for the overall transimpedance of several amplifiers as well as measured results are presented. Finally, an OEIC in a 1.0-mm CMOS technology with a polysilicon Resistor instead of a MOS Feedback Resistor with a data rate of 1 Gbit/s for 638 nm is shown. The sensitivity of this OEIC is improved by at least 9 dBm over that of published OEICs. © 2003 Society
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A transmission-line approach for modeling Feedback Resistors in integrated transimpedance amplifiers
IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications, 2003Co-Authors: J. Knorr, Horst ZimmermannAbstract:Based on the transmission-line model, the grounded uniformly distributed RC line (URC) is used to investigate the behavior of the Feedback Resistor used in transimpedance amplifiers (TIAs). Due to their strong capacitive coupling to substrate ground, polysilicon Resistors used in the Feedback circuit contribute to the frequency response of the overall amplifier. This may result in limitations in bandwidth, signal distortion and even instability. A simple and descriptive model is derived to find design formulas to optimize the overall amplifier including its Feedback capacitor and to show an upper performance limit for an idealized amplifier with high gain. Simulation results based on the approximation model and on the exact URC model are delivered for both an idealized as well as for a real amplifier.
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High-performance receivers for optical interconnects in standard MOS technology
Optoelectronic Interconnects VIII, 2001Co-Authors: Horst Zimmermann, T. Heide, Holger PlessAbstract:Novel monolithic optical receivers in 0.8 micrometers standard MOS technology with NRZ data rates in excess of 531 Mb/s at 850 nm are introduced. At 638 nm the data rates are above 622 Mb/s. The innovative integrated double photodiode allowing this high speed without any modification in a CMOS process is described and results for their quantum efficiency and for their transient response are presented. Furthermore the improvement of the sensitivity of the photodiodes and the OEICs by an antireflection coating is discussed. The circuit topology of the OEICs is described. A transimpedance input stage with an active MOS Feedback Resistor is implemented. Analytical calculations for the bandwidth and for the effective transimpedance of the amplifiers as well as measured results are presented. Finally, an OEIC in a 1.0 micrometers CMOS technology with a polysilicon Resistor instead of a MOS Feedback Resistor and implementing a pin photodiode achieves a data rate of 1 Gb/s for 638 nm. The sensitivity of this OEIC is improved by 9 dB m compared to that of a published OEIC.
