Showing papers on "Output impedance published in 2008"

Analysis and Optimization of Switched-Capacitor DC–DC Converters

Abstract: Analysis methods are developed that fully determine a switched-capacitor (SC) dc-dc converter's steady-state performance through evaluation of its output impedance. This analysis method has been verified through simulation and experimentation. The simple formulation developed permits optimization of the capacitor sizes to meet a constraint such as a total capacitance or total energy storage limit, and also permits optimization of the switch sizes subject to constraints on total switch conductances or total switch volt-ampere (V-A) products. These optimizations then permit comparison among several switched-capacitor topologies, and comparisons of SC converters with conventional magnetic-based dc-dc converter circuits, in the context of various application settings. Significantly, the performance (based on conduction loss) of a ladder-type converter is found to be superior to that of a conventional magnetic-based converter for medium to high conversion ratios.

Ultra-Wideband Power Divider With Good In-Band Splitting and Isolation Performances

Abstract: An ultra-wideband (UWB) power divider on microstrip line is proposed, analyzed and designed. This divider is formed by installing a pair of stepped-impedance open-circuited stubs and parallel-coupled lines to two symmetrical output ports. In addition, a single resistor is properly placed between two output ports. After simple transmission line theory analysis, it is demonstrated that 3 dB power splitting from one input to two output ports, good impedance matching at all the three ports and excellent isolation between two output ports are achieved over the specified 3.1-10.6 GHz UWB range. Finally, a prototype divider is fabricated and measured to provide an experimental verification on the predicted attractive features.

Advanced Renewable Energy Harvesting

Abstract: The power of DC electrical sources is combined onto a DC buss, such that each source behaves independently from any other source attached to the buss. In one embodiment, a converter module is attached to each of a plurality of solar photovoltaic panels and its output is attached in a parallel manner to a common buss that forms the input to a DC AC inverter. The converter module includes a Maximum Power Point Tracking component that matches the output impedance of the panels to the input impedance of the converter module. The converter also includes a communication component that provides parametric data and identification to a central inverter. Data generated by each converter module is transmitted over the power line or by wireless means and is collected at the inverter and forwarded to a data collection and reporting system.

Small-signal input impedance modeling of line-frequency rectifiers

Abstract: This paper presents a systematic method for modeling small-signal input impedance of line-frequency AC-DC converters. The objective is to develop proper models that can be used for stability analysis of AC power systems with significant DC loads powered by such converters. The proposed modeling method uses harmonic linearization and Fourier analysis techniques to describe the current and voltage mapping process through the converter switching circuit. The voltage and current mapping relations are then combined to give an impedance mapping model which converts the impedance of any circuit or system connected to the DC output of converter into a corresponding small-signal input impedance of the converter at the AC side. Similar relations can be used to map the AC source impedance into the DC side to give the equivalent dc source impedance for stability analysis of the DC subsystem. This paper focuses on the basic principle of the impedance mapping method and uses a single-phase diode rectifier circuit to demonstrate the modeling process. The resulting ac input impedance model is validated by detailed circuit simulation as well as experimental measurements.

Current-Mode Multiphase Sinusoidal Oscillator Using Current Differencing Transconductance Amplifiers

Abstract: This paper describes a simple current-controlled current-mode multiphase sinusoidal oscillator based on current differencing transconductance amplifiers (CDTAs) as active components. The proposed oscillator circuit, which employs only one CDTA and one grounded capacitor for each phase, can generate arbitrary n current-output signals (n being even or odd) equally spaced in phase, all at high output impedance terminals. The oscillation condition and the oscillation frequency can be controlled electronically and independently through the bias current of the CDTA. The oscillator has low-component count, low-sensitivity performance, and is highly suitable for monolithic implementation. PSPICE simulation results are given to confirm the operation of the proposed oscillator.

Modeling and Design for a Novel Adaptive Voltage Positioning (AVP) Scheme for Multiphase VRMs

Abstract: Adaptive voltage positioning (AVP) has been used in multiphase voltage regulator module (VRM) applications. A novel scheme, called AVP+, is analyzed in this paper. Small signal model is used to look into the control performance issues such as output impedance and stability. The model has been verified in the experiments and simulations. Compared to a conventional AVP schemes, the present scheme provides better stability margin and output- impedance performance. This is especially true for the prevailing trend of using ceramic output capacitors and high switching frequency. The focus of the present paper is the small-signal modeling for control loop design using the AVP+ scheme which was never analyzed before. And the comparisons were made between AVP+ and AVP- on the stability and output impedance performance.

Electrical Impedance Tomography of brain function

Abstract: Electrical impedance tomography is recently developed imaging technique, with which images of the internal impedance of the subject can be rapidly collected with rings of external ECG - type electrodes. It is fast, inexpensive, portable and is very sensitive to physiological changes which affect the electrical impedance properties. Set against this is a relatively poor spatial resolution and ill posed nature of the procedure for reconstructing images, such that a small errors due to instrumentation translate into large errors in images. For about two decades, satisfactory images have been obtained of changes over time related to gastric emptying and ventilation and cardiac output in the thorax. The main work of the speakerpsilas group has been to adapt existing EIT designs for the demanding application of imaging changes in the brain due to conditions like stroke, epilepsy or normal physiological brain activity; the difficulty is that the skull is resistive and diverts current so that the signal to noise ratio is low. In addition, imaging of acute stroke requires one-off images where the use of time difference to correct for instrumentation errors is not possible. Approaches used to overcome these problems include the use of signal processing, improved numerical models for image reconstruction, and the use of frequency difference imaging.

A Simple Control Method for High-Performance UPS Inverters Through Output-Impedance Reduction

Abstract: The purpose of a voltage controller for uninterruptible-power-supply inverters is to produce stable output voltage with low distortion under all loading conditions, particularly under nonlinear loads and load transients. Since the output impedance of the inverter is the source for tracking error caused by load current, this paper proposes a simple digital feedback controller that focuses on reducing the output impedance of inverters by a feedback of the load current. The proposed control strategy ensures high-quality steady-state and dynamic responses from the inverter system. The design of the proposed digital controller is simple and requires only a reasonably accurate knowledge of the output L-C filter parameters. In addition, only the output voltage and the load current are sensed if the dc link voltage is constant. The results of simulations and experiments show that the proposed controller can achieve very low total harmonic distortion and fast dynamic response under varied loads including nonlinear loads with low switching frequency.

Maximum power point tracking using the optimal duty ratio for DC-DC converters and load matching in photovoltaic applications

Abstract: The purpose of this paper is to present an alternative maximum power point tracking, MPPT, algorithm for a photovoltaic module, PVM, to produce the maximum power, Pmax, using the optimal duty ratio, D, for different types of dc-dc converters and load matching. The proposed algorithm has the advantages of maximizing the efficiency of the power utilization, can be integrated to other MPPT algorithms without affecting the PVM performance, is excellent for real-time applications and is a robust analytical method, different from the traditional MPPT algorithms which are more based on trial and error, or comparisons between present and past states. The procedure to calculate the optimal duty ratio for a buck, boost and buck-boost converters, to transfer the maximum power from a PVM to a load, is presented in the paper. Additionally, the existence and uniqueness of optimal internal impedance, to transfer the maximum power from a photovoltaic module using load matching, is proved. Finally, results are presented in the paper.

Background Calibration of Pipelined ADCs Via Decision Boundary Gap Estimation

Abstract: A method of indirect background digital calibration of the dominant static nonlinearities in pipelined analog-to-digital converters (ADC) is presented. The method, called decision boundary gap estimation (DBGE), monitors the output of the ADC to estimate the size of code gaps that result at the decision boundaries of each stage. Code gaps result from such effects as capacitor mismatch, finite opamp gain, finite current source output impedance, comparator offset, and charge injection. DBGE does not require special calibration signals or additional analog hardware and can even reduce the performance requirements of the analog circuitry. The calibration is performed using the input signal and thus requires that the input signal exercise the codes in the vicinity of the decision boundaries of each stage. If it does not exercise these codes, then lack of calibration is less critical because the nonlinearities will not appear in the output signal. DBGE is simple and amenable to hardware and/or software implementations. Simulation results indicate DBGE is highly accurate, robust, and adaptive even in the presence of parameter drift and circuit noise.

Dynamic impedance matching in RF resonator cavity

Abstract: A method for matching an impedance of a system comprising a cavity and one or more feeds to an impedance of one or more sources of electromagnetic radiation irradiating a plurality of frequencies into the cavity via the feeds, comprising: determining a plurality of s-parameter of the system for a frequency band; determining the system impedance based on the s-parameters; and modifying the system impedance according to the difference between the impedance of the system and the impedance of the source.

System and method for controlling power based on impedance detection, such as controlling power to tissue treatment devices

Abstract: A system and method of controlling the application of energy to tissue using measurements of impedance are described. The impedance, correlated to the temperature, may be set at a desired level, such as a percentage of initial impedance. The set impedance may be a function of the initial impedance, the size and spacing of the electrodes, the size of a targeted passageway, and so on. The set impedance may then be entered into a PID algorithm or other control loop algorithm in order to extract a power to be applied to a treatment device.

Effects of X Capacitors on EMI Filter Effectiveness

Abstract: The suppression mechanism of the differential-mode noise of an X capacitor in offline power supplies is, for the first time, attributed to two distinct concepts: 1) impedance mismatch (regarding a line impedance stabilization network or mains and the equivalent power supply noise source impedance) and 2) C(dv/dt) noise current balancing (to suppress mix-mode noise). The effectiveness of X capacitors is investigated with this theory, along with experimental supports. Understanding of the two aforementioned mechanisms gives better insight into filter effectiveness, which may lead to a more compact filter design.

Low-noise current excitation sub-system for medical EIT.

Abstract: Electrical impedance tomography (EIT) has many potential applications in medicine. The sensitivity and spatial resolution of EIT can be enhanced significantly by increasing the measurement signal-to-noise ratio (SNR), to which a significant contribution is made by the SNR of the current excitation sub-system. In this paper we present a prototype EIT current excitation sub-system with 80 dB SNR, exploiting both digital and analogue techniques. It uses digital waveform synthesis, a 16-bit DAC and subsequent reconstruction filter, to drive an enhanced Howland current source. Detailed analysis and testing of the current sub-system are presented. Its output impedance is 10 MΩ for different load impedances, varying slowly over the frequency range from 10 kHz up to 4 MHz.

High output impedance current-mode all-pass sections with two grounded passive components

Abstract: Two new first-order, current-mode all-pass sections, each with high output impedance and requiring only two grounded passive components along with a differential voltage current conveyor, are presented. The new circuits require no matching conditions for the realisation of current transfer functions and are simpler than most of the recently available circuits. The effect of parasitics and non-idealities is also considered. PSPICE simulations using 0.5 µ CMOS parameters confirm the validity and practical utility of the proposed circuits. A typical application in realising a new current-mode quadrature oscillator is given. A four-phase quadrature oscillator with high impedance outputs is also given.

Frequency selective amplifier with wide-band impedance and noise matching

Abstract: This disclosure is directed to a frequency-selective low noise amplifier (LNA) with wide-band impedance and noise matching. The LNAS may include a closed loop circuit that supports wideband input matching. For example, the closed loop circuit may be configure to impedance match an input signal and provide a low noise figure. In addition, the LNA may include an open loop circuit that amplifies the input signal and provides a high output impedance. The open loop circuit may further include a selectivity filter that filters out frequencies outside a desired frequency band. The LNA may drive a tunable band-pass filter via the open loop circuit.

Development of a portable therapeutic and high intensity ultrasound system for military, medical, and research use

Abstract: We have developed a portable high power ultrasound system with a very low output impedance amplifier circuit (less than 0.3 Omega) that can transfer more than 90% of the energy from a battery supply to the ultrasound transducer. The system can deliver therapeutic acoustical energy waves at lower voltages than those in conventional ultrasound systems because energy losses owing to a mismatched impedance are eliminated. The system can produce acoustic power outputs over the therapeutic range (greater then 50 W) from a PZT-4, 1.54 MHz, and 0.75 in diameter piezoelectric ceramic. It is lightweight, portable, and powered by a rechargeable battery. The portable therapeutic ultrasound unit has the potential to replace "plug-in" medical systems and rf amplifiers used in research. The system is capable of field service on its internal battery, making it especially useful for military, ambulatory, and remote medical applications.

Method and arrangement for matching an antenna

Abstract: A method and an arrangement for matching the antenna of a radio device in transmitting condition The antenna impedance in the output of the power amplifier of a transmitter is adjusted by means of a π-shaped reactive matching circuit, the component values of which can be selected from a relatively wide array of the alternatives The component values are selected by means of the multiple-way switches, which only are located in the transverse branches of the matching circuit The switches are set (706) by the control unit, input variables of which being the SWR value provided by the directional coupler, the operating band used each time and a value of the transmitting power The matching is based on an adjusting process to be executed at regular intervals, in which process the control unit tries different combinations of the switch states and finally selects (710) the combina¬ tion, which brings the lowest SWR value In the beginning of the adjusting process the control unit reduces (705), on grounds of the current values of the input variables, the number of the combinations to be tried The antenna matching maintains relatively good, although the internal output impedance of the amplifier and the impedance from the output towards the antenna would strive to differ from each other for external reasons, a band changing or a change in the outptut power

Compact subnanosecond high voltage pulse generation system for cell electro-manipulation

Abstract: Disclosed are methods and systems for subnanosecond rise time high voltage (HV) electric pulse delivery to biological loads. The system includes an imaging device and monitoring apparatus used for bio-photonic studies of pulse induced intracellular effects. The system further features a custom fabricated microscope slide having micro-machined electrodes. A printed circuit board to interface the pulse generator to the micro-machined glass slide having the cell solution is disclosed. An low-parasitic electronic setup to interface with avalanche transistor-switched pulse generation system is also disclosed. The pc-board and the slide are configured to match the output impedance of the pulse generator which minimizes reflection back into the pulse generator, and minimizes distortion of the pulse shape and pulse parameters. The pc-board further includes a high bandwidth voltage divider for real-time monitoring of pulses delivered to the cell solutions.

Controlling for variable impedance and voltage in a memory system

Abstract: A memory interface device, system, method, and design structure for controlling for variable impedance and voltage in a memory system are provided. The memory interface device includes a calibration cell configurable to adjust an output impedance relative to an external reference resistor, and driver circuitry including multiple positive drive circuits and multiple negative drive circuits coupled to a driver output in a memory system. The memory interface device further includes impedance control logic to adjust the output impedance of the calibration cell and selectively enable the positive and negative drive circuits as a function of a drive voltage and a target impedance.

A highly linear bulk-driven CMOS OTA for continuous-time filters

Abstract: In this paper we present a bulk-driven CMOS triode-based fully balanced operational transconductance amplifier (OTA) and its application to continuous-time filters. The proposed OTA is linearly tunable with the feature of low distortion and high output impedance. It can achieve wide input range without compromising large transconductance tuning interval. Using a 0.18 ¼m n-well CMOS process, we have implemented a third-order elliptic low-pass filter based on the proposed OTA. Both the simulation and measurement results are reported. The total harmonic distortion is more than -45 dB for fully differential input signals of up to 0.8 V peak---peak voltage. A dynamic range of 45 dB is obtained under the OTA noise integrated over 1 MHz.

Source-gated thin-film transistors

Abstract: The on-current of a source-gated transistor is determined by the current passing through a reverse biased source barrier. Since this current is field-dependent, it can be controlled using a gate located directly opposite the source barrier. This concept leads to major changes in thin-film transistor behaviour compared with the standard FET. In particular saturation voltages, short channel effects and excess carrier concentrations are reduced while internal electric fields are enhanced. These features lead to lower power dissipation and higher output impedance compared with a FET as well as improvements in stability and speed. The SGT is particularly useful for high-performance circuits in poor-quality semiconductors.

Method for automatic impedance matching for a radiofrequency circuit and transmission or reception system with automatic matching

Abstract: The invention relates to a method for automatically matching the antenna impedance for a radiofrequency transmission circuit having an amplifier. An impedance matching network is inserted between the amplifier and the antenna. The output current i and voltage V from the amplifier and their phase shift are measured, and from this the complex impedance, defined by V/i, is deduced. The antenna impedance is calculated as a function of this complex impedance and as a function of the known present values of the adjustable impedances of the matching network. New values are calculated, from the calculated value of the antenna impedance, for the adjustable impedances of the matching network that allow an overall load impedance of the amplifier to be obtained which is as close as possible to the nominal load impedance Z opt of the amplifier, and the matching network is controlled to adjust the adjustable impedances to these new values.

Resonance impedance sensing of human blood cells

Abstract: A challenging problem in alternating current (AC) impedance sensing of particles (e.g., blood cells in plasma) with micro electrodes is that with the shrinking of electrode surface area the electrode double layer capacitance decreases. This double-layer capacitor dominates the system impedance in lowfrequency range, while the parallel stray capacitor dominates the system impedance in high frequency range. Hence the sensitivity for particle sensing for micro impedance sensors decreases over a wide frequency range. In this paper, we propose an approach to solve the problem. The idea is to use resonant sensing by connecting an external parallel inductor to the system. At the resonant frequency, the capacitive components in the system are nullified by the inductor, leaving the channel impedance (including the particle impedance) to be a major component in the system impedance. We then successfully demonstrate this idea by sensing 5 µm polystyrene beads. More important, this technique is extended to sensing blood cells in diluted human whole blood and leukocyte-rich plasma. The sensitivity can be improved by two orders of magnitude over more than three decades in frequency domain. The measured signal peak height histogram at low frequency matches well with known volume distribution of erythrocytes and leukocytes.

A ferroelectric-based impedance tuner for adaptive matching applications

Abstract: A general purpose impedance tuner is proposed for adaptive matching applications to compensate the impedance variations of devices such as antennas or power amplifiers. The impedance tuner, composed of a phase shifter and a variable transformer, is designed based on all-pass networks. Thin-film barium-strontium titanate (BST) parallel-plate capacitors fabricated on sapphire are used as the tuning elements. The impedance tuner is completed by mounting chip inductors and blocking capacitors on the same substrate. On-wafer measurement results show that, at 1.8 GHz, impedance transformation ratio of 4 can be achieved and the dissipation loss for all biasing voltages (0 to 18 V) is less than 5.5 dB.

Harmonic termination of power amplifiers using BAW filter output matching circuits

Abstract: A system, apparatus and method for providing filtering functionality and impedance transformation within a BAW resonator network are disclosed. In particular, a BAW resonator network is designed to provide bandpass capability and a transformation between its input impedance and output impedance. By effectively integrating impedance matching functionality within the BAW resonator network, discrete impedance matching elements previously required within a system may be removed or reduced in size. As a result, matching networks and their associated component costs, insertion losses, and board size contributions may be reduced. Harmonic termination may be provided within the BAW resonator network or a prematch stage to improve efficiency of a power amplifier.

Coupling circuitary for impedance adaptation in power line communications using VCGIC

Abstract: The access impedance of the power line channel is time variant. This feature of the power line channel is the main cause of impedance mismatching between the access impedance of the power line channel and the output impedance of the power line communication system and impedance mismatching lead to the problem of reducing the communication range. Therefore, it is very important to match between the access impedance of the power line channel and the output impedance of the power line communication system for the expansion of the communication range. The impedance matching can be achieved to change the output impedance of the line coupling circuitary. In this paper, the voltage controllable inductance circuit, which is composed of resistors, capacitors and OP-AMPs, is applied to the proposed line coupling circuitary. The proposed line coupling circuitary is smaller and more flexible than other existing line coupling circuitary for the adaptation to channel. Though, the proposed line coupling circuitary has the limited operation range, the maximum power transmission is achieved in the limited range. The proposed line coupling circuitary is simulated and measured to confirm its performances.

A 20Gb/s SerDes transmitter with adjustable source impedance and 4-tap feed-forward equalization in 65nm bulk CMOS

Abstract: The design and wafer probe test results of a 20 Gb/s Source-Series Terminated SerDes transmitter are presented. The integrated circuit, fabricated in a 65 nm bulk CMOS technology, transmits pre-emphasized data through the use of a 4-tap feed-forward equalizer. Transmitter output impedance is adjustable from 45 to 55 ohms. A power consumption of 167 mW at 1.1 V was measured at a transmit rate of 20 Gb/s.

Device, method and system for estimating the termination to a wired transmission-line based on determination of characteristic impedance

Abstract: A system and method for measuring a characteristic impedance of a transmission-line comprises transmitting energy to the line, and shortly after measuring the voltage/current involved and thus measuring the equivalent impedance. The measured characteristic impedance may then be used in order to determine the termination value required to minimize reflections. In another embodiment, the proper termination is set or measured by adjusting the termination value to achieve maximum power dissipation in the terminating device. The equivalent characteristic impedance measurement may be used to count the number of metallic conductors connected to a single connection point. This abstract is not intended to limit or construe the scope of the claims.