Value Of Load Impedance Research Articles

The Design and Analysis of a 25-Watt Broad-Band GaN HEMT-Based Power Amplifier

This paper presents the novel design and analysis of a 25 W broadband Class-AB GaN HEMT-based power amplifier working over 0.9–1.7 GHz. A large signal model of the Wolfspeed-make GaN HEMT CG2H40025 has been used in this design. The comprehensive design process has been carried out with the help of the Advanced Design System software by Keysight. Instead of conjugately matching the load and source impedance obtained from load-pull analysis of a nonlinear model of CG2H40025, the value of load and source impedance has been tuned with the help of a novel design approach of an ideal matching design approach. Thus, to achieve an output power of more than 25 W and a flat large signal gain of 15.425 ± 0.375 dB, a novel design approach has been employed to create input and output matching networks, maintaining a lower Q value results in broad bandwidth and for determining the load and source impedances. The circuit has been fabricated on Roger’s substrate RO4350B having a dielectric constant of 3.66 and a loss tangent of 0.0031. The unique design approach based on electromagnetic simulation of the circuit at each design step yielded experimental results that agreed very well with the simulated results. The fabricated power amplifier achieves a power-added efficiency of over 54.78% and a drain efficiency of over 55.45% throughout the entire frequency range. It also delivers a maximum output power of 32.18 W at 1.3 GHz. This power amplifier is developed for L-band Foliage Penetrating Radar.

Wideband Chebyshev Impedance Transformer Set with Very Low Reflection Coefficient

In various electronic and electrical devices for communication systems, impedance transformers with wide bandwidths are important. In this article, Chebyshev impedance transformers for ohmic loads with order 3 are presented at different frequencies and load impedance values using Duroid and FR4 substrates (εr = 2.2 and εr = 4.4 respectively). Simulated results are shown using the software Advanced Design System (ADS). The thickness of the substrate for FR4 dielectric material is 1.544 mm and for Duroid material is 1.27mm. The matching transformers were performed at 1 GHz, 1.5 GHz, 2 GHz, and 1.5 GHz for two load impedance 100 Ohms and 75 Ohms from 50 Ohms showing a reflection coefficient Γm = 0.05. The S11 scattering parameter was obtained.

Online Monitoring of Voltage Stability Margin in Kosovo Power System Using Local Measurements

This paper presents an analysis of the voltage stability of the Kosovo power system. The first part of the study has included a detailed analysis of the Kosovo power system by using the continuous power flow method, with an emphasis on the determination of the P–V curve of voltage stability. Thus, it has identified the weak and critical points of the power system in terms of voltage stability and has defined the margin of instability. In order to achieve online monitoring of voltage stability in the power system, it is proposed to place phasor measurement units in the weakest critical buses. Furthermore, the Thevenin equivalent method has been applied to evaluate voltage stability in the critical buses. The maximum transmissible real power to the weak buses in the system can be achieved when load impedance is equal to the Thevenin impedance. The load and Thevenin impedance values have been obtained from the relevant PMU data. Following online monitoring of voltage stability in the power system, the developed voltage stability load bus index can be used as useful information by system operators in order to undertake appropriate countermeasures to prevent voltage collapse.

LSE Precoder for Load Modulated Arrays With Channel Modulation

In this letter, we consider novel multiuser precoding techniques suited for load modulated arrays (LMAs) on the downlink, wherein a base station employs an LMA to transmit data to multiple users. For implementation simplicity, it is desired that the antenna load impedance values in the LMA are drawn from a discrete set. For such LMAs with discrete-valued load impedances, we propose an iterative precoding algorithm using the least square error (LSE) framework. For the same setting, we also propose a precoding scheme that employs channel modulation (CM) using radio frequency (RF) mirrors in each element of the LMA. This LMA-CM precoding scheme tunes the RF mirrors as well as antenna load modulators such that the instantaneous constraint of constant hypersphere signaling from a discrete set required for LMAs is satisfied. Improved distortion and bit error performance of the proposed schemes are reported.

Prediction of odd-mode instabilities under output mismatch effects

A methodology is presented to predict odd-mode instability in power amplifiers under output mismatch effects, as in the case of amplifiers connected to an antenna. This kind of instability is often observed in multi-device configurations, due to their symmetry properties. Unlike the single-ended situation, there is a cancellation of odd multiples of the oscillation frequency at the circuit output, so there is no impact of the load-impedance values at the sideband frequencies. The odd-mode instability only depends on the impedance terminations at the fundamental frequency and its harmonic terms, and can only be detected within the circuit unstable loop, instead of the antenna-connection terminals. The possible unstable modes are related with the eigenvectors of an outer tier conversion matrix accounting for the symmetry properties of the circuit topology. Under sufficient low-pass filtering of the amplifier output network, the analysis parameters can be limited to the magnitude and phase of the reflection coefficient at the fundamental frequency. This analysis involves a computationally efficient graphical technique to detect potential instabilities and a bifurcation-detection method to determine the instability boundaries in the Smith chart. The two main types of instability from periodic regime are considered, respectively associated with incommensurable and subharmonic oscillations. Results have been validated through pole-zero identification and experimental measurements.

Spatial Multiplexing of OFDM Signals With QPSK Modulation Over ESPAR

An electronically steerable parasitic array radiator (ESPAR) transmitter, employing one active and one parasitic antenna element, which can simultaneously transmit two orthogonal frequency division multiplexing (OFDM) signals with quadrature phase shift keying (QPSK) modulation via spatial multiplexing, is developed. In particular, a minimum mean square error (MMSE) scheme for quantizing the parasitic load impedance is developed to reduce the number of distinct load impedance values that should be realized for spatial multiplexing over ESPAR. To this end, the probability density function of the parasitic load impedance is derived, and the realizable region of the load impedance is analyzed. It is observed that the resistance of the active antenna element should be large enough to transmit OFDM signals. The characteristics of two existing ESPAR antennas with different mutual coupling matrices are examined, and it is observed that the one with the larger active antenna resistance is suitable for OFDM transmission. The bit error rate (BER) and the receive error vector magnitude performances of the proposed ESPAR systems with 6/8-bit quantizers and zero-forcing (ZF) receiver are compared with those of the corresponding ideal multiple-input multiple-output (MIMO) system through computer simulation. The results demonstrate that the performances of the proposed ESPAR with the 8-bit quantizer and the ideal MIMO systems can be almost identical, whereas the proposed ESPAR with the 6-bit quantizer exhibits some performance loss.

Exploiting Constructive Mutual Coupling in P2P MIMO by Analog-Digital Phase Alignment

In this paper, we propose a joint analog-digital (A/D) beamforming scheme for the point-to-point multiple-input-multiple-output system, where we exploit mutual coupling by optimizing the load impedances of the transmit antennas. Contrary to the common conception that mutual coupling strictly harms the system performance, we show that mutual coupling can be beneficial by exploiting the concept of constructive interference. By changing the value of each load impedance for the antenna array based on convex optimization, the mutual coupling effect can be manipulated so that the resulting interference aligns constructively to the useful signal vector. We first prove that the full elimination of mutual coupling effect is not achievable solely by tuning the values of the antenna load impedances. We then introduce the proposed A/D scheme for both PSK and QAM modulations, where performance gains with respect to conventional techniques are obtained. The implementation of the proposed schemes is also discussed, where a lookup table can be built to efficiently apply the calculated load impedances. The numerical results show that the proposed schemes can achieve an improved performance compared to systems with fixed mutual coupling, especially when the antenna spacing is small.

A 600W broadband doherty power amplifier with improved linearity for wireless communication system

An asymmetric Doherty architecture based on three identical transistors is proposed in this paper. This proposed three-way topology reduces the difficulty in designing matching networks brought by the low optimal impedance of high power transistors. And the inverted Doherty topology as well as carefully chosen value of load impedance makes it possible to extend the bandwidth of high power amplifiers. Besides, bias networks of this proposed three-way architecture are also carefully considered to improve the linearity. The proposed high power three-way Doherty power amplifier (3W-DPA) is designed and fabricated based on theoretic analysis. Its maximum output power is about 600Watts and the drain efficiency is above 35.5% at 9dB back off output power level from 1.9GHz to 2.2 GHz and the saturated drain efficiency is above 47% across the whole frequency band. The measured concurrent two-tone results suggest that the linearity of DPA is improved by at least 5dB.

Analysis and Design of Dynamic Buck Converter with Change in Value of Load Impedance

DC-DC Converter is a tool that is able to use for changing value of DC voltage to another value. DC-DC Converter commonly used in electronic system, for instance Personal Computer, telecommunication system, driver motor DC, and also used as charge controller for battery. This equipment is able to replace voltage regulator which has so much power dissipation. DC-DC converter has some of types; those are Buck Converter, Boost Converter, and Buck-Boost Converter. Each type of DC-DC Converter has their respective functions.Buck Converter is useful as step down of the voltage value, so the output voltage will be decreased. DC-DC Converter of this type commonly used when the supply voltage from the source is too much for an electronic system as when the charging battery by solar panel, by using Buck Converter when supply voltage from solar panel exceed battery voltage charging then the voltage can be dropped to the value of battery charging. Therefore, battery lifetime can be safe, and also other electronic devices which use Buck Converter.Buck converter has some primary components in its implementation, that is, MOSFET as fast as electronic switching, diode, inductor, and capacitor. To acquire, the optimal result should be noted the proper component selection. In this research, the writer tried to select inductance value of inductor and capacitance value of capacitor by simulating on MULTISIM, in order to get output as well as theoretical calculation and analyze the transient-state and the steady-state of the Buck Converter output. On the other hand, this research was conducted several variations of load for selected inductor and capacitor.

Nanoscale Electromagnetic Compatibility: Quantum Coupling and Matching in Nanocircuits

The paper investigates two typical electromagnetic compatibility (EMC) problems, namely, coupling and matching in nanoscale circuits composed of nano-interconnects and quantum devices in entangled state. Nano-interconnects under consideration are implemented by using carbon nanotubes or metallic nanowires (NWs), while quantum devices by semiconductor quantum dots. Equivalent circuits of such nanocircuits contain additional elements arising at nanoscale due to quantum effects. As a result, the notions of coupling and impedance matching are reconsidered. Two examples are studied: in the first one, electromagnetically coupled NWs are connected to classical lumped devices; in the second one, electromagnetically uncoupled transmission lines are terminated on quantum devices in entangled states. In both circuits, the EMC features qualitatively and quantitatively differ from their classical analogs. In the second example, we demonstrate the existence of quantum coupling, due to the entanglement, which exists in spite of the absence of classical electromagnetic coupling. The entanglement also modifies the matching condition introducing a dependence of the optimal value of load impedance on the line length.

Stability Analysis of Power Amplifiers Under Output Mismatch Effects

Novel criteria are presented for small- and large-signal stability analysis of microwave circuits under output mismatch effects. They are based on concepts from bifurcation theory, which enable the derivation of general equations for the stability boundaries that depend on the termination load. The boundary calculation does not require any optimization of the circuit parameters. Instead, it is based on the direct calculation of an admittance function obtained through circuit linearization about either the dc solution, in the small-signal stability analysis, or the periodic solution, in the large-signal one, with low computational cost. As will be demonstrated both with homotopy and bifurcation concepts, the Hopf locus obtained in this way delimits a stable region and a potentially unstable one. In a large-signal stability analysis, the sidebands that influence the stability properties are identified, which depend on the particular amplifier topology and its filtering effects. The stability boundaries are then calculated with the conversion matrix approach for all load impedance values at the relevant harmonic and sideband frequencies. For the derivation of absolute stability conditions, a new scattering type matrix is proposed describing the circuit response from the output reference plane with respect to the two sidebands about the input carrier. The new methodologies and formulations have been validated by independent simulations using pole-zero identification, and by measurements.

High-power CMOS current driver with accurate transconductance for electrical impedance tomography.

Current drivers are fundamental circuits in bioimpedance measurements including electrical impedance tomography (EIT). In the case of EIT, the current driver is required to have a large output impedance to guarantee high current accuracy over a wide range of load impedance values. This paper presents an integrated current driver which meets these requirements and is capable of delivering large sinusoidal currents to the load. The current driver employs a differential architecture and negative feedback, the latter allowing the output current to be accurately set by the ratio of the input voltage to a resistor value. The circuit was fabricated in a 0.6- μm high-voltage CMOS process technology and its core occupies a silicon area of 0.64 mm (2) . It operates from a ± 9 V power supply and can deliver output currents up to 5 mA p-p. The accuracy of the maximum output current is within 0.41% up to 500 kHz, reducing to 0.47% at 1 MHz with a total harmonic distortion of 0.69%. The output impedance is 665 k Ω at 100 kHz and 372 k Ω at 500 kHz.

The minimization of the extraneous electromagnetic fields of an inductive power transfer system

The efficiency of inductive wireless power transfer (IPT) systems has been extensively studied. However, the electromagnetic compatibility of such systems is at least as important as the efficiency and has received much less attention. We consider the net magnetic dipole moment of the system as a figure of merit. That is, we seek to minimize the magnitude of the net dipole moment in order to minimize both the near magnetic fields and the radiated power. A 20 kHz, 3.3 kW, IPT system, representative of typical wireless vehicular battery charging systems, is considered and it is seen that one particular value of load impedance minimizes the net dipole moment while another, distinct, value maximizes efficiency. Thus, efficiency must be traded off, at least to some extent, in order to minimize extraneous electromagnetic fields.

99/01281 Hydroelectric generation scheduling an application of genetic-embedded fuzzy system approach : Huang, S.-J. Electric Power Systems Research, 1998, 48, (1), 65–72

This paper presents a critical review on the self-excitation process and steady state analysis of a self-excited induction generator driven by the wind turbine. The physics of self-excitation is crucial for the interpretation of the voltage build-up process of self-excited induction generators (SEIGs). During the initial phase of build-up the machine behaves as if it be a synchronous machine with weak permanent magnet in the form of remnant magnetization. In this paper the MMF approach as well as the synchronous resonance approach has been proposed to know the fact that how the machine relinquishes the initial synchronous mode and enters into the final asynchronous mode. The process of self-excitation is initiated by the resonating interaction between the terminal capacitor and machine׳s magnetizing reactance. The steady state analysis has been reviewed and proposed based on input/output impedance method to find the steady state reactive VAR need of the SEIG. The minimum and maximum critical capacitance has been evaluated theoretically. Finally the value of critical speed and critical load impedance has been evaluated.

A novel AC current source for capacitance-based displacement measurements

A 100 kHz bandwidth AC current source suitable to be used with capacitive sensors in displacement measurement applications has been designed and constructed. The high output impedance of the source is obtained by sensing the load voltage with a buffer stage having very low input capacitance. The sensing-buffer power supply, its shield, and the input shielding connections are driven at the buffer input potential in such a way that the effect of all input parasitic admittances, including the buffer common-mode impedance, are almost suppressed. The load impedance variations, which are directly proportional to displacements, are monitored by the output voltage of the sensing buffer. Measurements made at different frequencies with calibrated capacitance loads ranging from (1 to 20) pF have shown that the load-impedance values are proportional to the output voltage of the sensing buffer with a linearity better than 4/spl times/10/sup -4/ and resolution of about 3/spl times/10/sup -5/ over a 1 kHz bandwidth of load variation signal. The features of the current source and its performance in a displacement measurement application are described.

Capacitance requirements of self-excited induction generators

A simple method for computing the minimum value of capacitance, C min. required for initiating voltage build-up in a three-phase self-excited induction generator (SEIG) is presented. Based on the steady-state equivalent circuit model, a consideration of the circuit conductances yields a sixth-degree polynomial in the per-unit frequency. The polynomial can be solved for real roots, which enables the value of C/sub min/ to be calculated. Critical values of load impedance and speed, below which the machine fails to self-excite irrespective of the capacitance used, are found to exist. Closed form solutions for C/sub min/ are derived for no-load and inductive loads. Using the same numerical approach, an interative procedure is developed for predicting the capacitance required for maintaining the terminal voltage at a preset value when the generator is supplying load. Experimental results obtained on a 2 kW induction machine confirm the feasibility and accuracy of the proposed methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Force and electrical Thevenin equivalent circuits and simulations for thickness mode piezoelectric transducers

A simple model is reported for thickness-mode piezoelectric elements used as ultrasonic transducers in measurement systems. The model represents the excitation system and transducer as a Thevenin mechanical equivalent for the transmitting mode and a Thevenin electrical equivalent for the receiving mode. Computer programs based on the model have been developed, and computer simulations to study the effects of backing materials, element areas, and excitation sources are reported. The nature in which the source impedance alters the Thevenin mechanical output impedance and its importance in determining peak transmission frequency and in computing acoustic coating layers for matching was found. A total transfer improvement of 28 dB was shown for epoxy-backed elements radiating into fluid with the transducer used as both transmitter and receiver by using high values of source and load impedances in contrast to low values. The model was found to agree closely with experimental data of a 2.7-MHz transducer. Subject Classification: 85.40; 80.70; 85.52.

Large-Signal Calculations for the Overdriven Varactor Upper-Sideband Upconverter Operating at Maximum Power Output

When a varactor frequency upconverter is used as the output device in a communications transmitter, it is often desirable to operate at maximum power output. For such operation, the design procedure includes a large-signal analysis under overdriven conditions, requiring the use of a computer for solution. Equations for the instantaneous varactor charge, current, and voltage are derived assuming that only three currents are present: those corresponding to the signal, pump, and output frequencies. Numerical solutions corresponding to maximum power output are obtained for both graded-junction and abrupt-junction varactors. Values of power output, conversion efficiency, input impedances, load impedance, and bias voltage are presented for ranges of drive level (1 to 2) and varactor quality (0.001 ≦ ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> &omega <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> 0.1) sufficient to include most practical designs.

Parallel Wire Susceptibility Testing for Signal Lines

A technique is presented which can be utilized to establish a standardized procedure for performing conducted susceptibility testing on signal lines at the component and/or the subsystem level. Typical military specifications require that the test function be injected to the test lines via a susceptibility transformer, a coupling capacitor, or a standardized network, such as the line stabilization network (LSN). Although these methods may be adequate for testing of power line susceptibility, they present several disadvantages when utilized in signal lines, such as impedance loading, the requirement for physical insertion, and proximity to the load. These disadvantages become more pronounced at RF where the signal developed across the input of the test specimen may be considerably lower than the signal injected at the physical insertion point. A technique that overcomes these deficiencies utilizes a coupling jig that 1) does not require a physical connection, and 2) provides a known coupling across the input impedance of the package being tested-thus simulating, in a very realistic manner, interference coupling as it may occur in a system. A general expression for coupling prediction and a computer solution for various values of load impedances are presented.

Calculation of the Maximum Efficiency of the Thermionic Converter

A theoretical analysis of the efficiency of a thermionic converter is made in terms of the following parameters: Va, the potential difference between the top of the potential barrier in the interelectrode space and the Fermi level of the anode; VL, the potential drop across a load impedance in series with the converter; and Vl, the potential drop in the necessary electrical connection to the cathode. The analysis is carried out by developing an expression for the efficiency of the converter and then maximizing this expression with respect to VL and Vl. This method yields optimum values of load impedance, cathode lead geometry, and cathode work function in terms of Va, cathode temperature, cathode emission constant (usually denoted by A), and effective emissivity of the cathode. A hypothetical example is worked out numerically and the results show that (1) a low value of Va is required for high efficiency, and (2) relatively low values of cathode work function are required for maximum efficiency at ordinary cathode temperatures.