Optimum Load Impedance Research Articles

Fundamental Aspects of Near-Field Coupling Small Antennas for Wireless Power Transfer

A physical limitation on the power transfer efficiency between two electrically small antennas in the near-field range is presented. By using a Z-parameter which describes the interaction between two antennas for spherical modes in connection with antenna parameters, the maximum power transfer efficiency and the optimum load impedance are shown as functions of the distance between two antennas, the radiation efficiency and the input impedance of the isolated antenna. The theory is verified by a simulation with a small helical antenna, which generates and modes, simultaneously.

Nonlinear characterization of GaN HEMT

DC I—V output, small signal and an extensive large signal characterization (load-pull measurements) of a GaN HEMT on a SiC substrate with different gate widths of 100 μm and 1 mm have been carried out. From the small signal data, it has been found that the cutoff frequencies increase with gate width varying from 100 μm to 1mm, owing to the reduced contribution of the parasitic effect. The devices investigated with different gate widths are enough to work in the C band and X band. The large signal measurements include the load-pull measurements and power sweep measurements at the C band (5.5 GHz) and X band (8 GHz). When biasing the gate voltage in class AB and selecting the source impedance, the optimum load impedances seen from the device for output power and PAE were localized in the load-pull map. The results of a power sweep at an 8 GHz biased various drain voltage demonstrate that a GaN HEMT on a SiC substrate has good thermal conductivity and a high breakdown voltage, and the CW power density of 10.16 W/mm was obtained. From the results of the power sweep measurement at 5.5 GHz with different gate widths, the actual scaling rules and heat effect on the large periphery device were analyzed, although the effects are not serious. The measurement results and analyses prove that a GaN HEMT on a SiC substrate is an ideal candidate for high-power amplifier design.

Asymptotic Solution for the Current Profile of Passive Bare Electrodynamic Tethers

A relatively high-accuracy analytical solution for the current and potential profile along a passive bare electrodynamic tether is provided using perturbation theory. An ad hoc nondimensional formulation of the governing local bias and orbital motion limited current collection equations allows one to approach the problem with a perturbation technique in which a parameter, epsilon, quantifies the influence of ohmic effects on the final solution. For the case of small ohmic effects an approximate solution is obtained with a third-order expansion. Conversely, the case of dominant ohmic effects is treated based on an extension of the exact analytical solution available for the particular case of zero load and negligible potential drop at the cathodic end of the tether. After computing the analytical current and potential profile the maximum and average current, the Lorentz force and torque, as well as the optimum load impedance for maximum power generation are obtained. When compared with the exact, numerically-computed solution an accuracy of better than 5 % is achieved for the computation of the average current across the full parameter space. The error with respect to the generated power becomes negligible when the load impedance is set to the optimum value, while it can grow to a maximum of about 30% for the less relevant case in which the load impedance of the power generation system is badly mismatched. The results, which are valid for a general rectilinear passive electrodynamic tether with constant cross section satisfying orbital motion limited theory and irrespective of the particular orbit configuration, will be of aid in the design and analysis of space missions involving bare electrodynamic tethers.

RF power performance evaluation of surface channel diamond MESFETs

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage V t ≈ 0–0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency f T and oscillation frequency f max) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point V DS = −14 V, V GS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.

DC and RF Degradation Induced by High RF Power Stresses in 0.18- $\mu\hbox{m}$ nMOSFETs

Both the degradations of dc and RF characteristics of nMOS transistors due to hot-carrier effect and instantaneous high RF power stresses are presented in this paper. The drain current, threshold voltage, output power, and power-added efficient were degraded after the output power exceeded the power capacity. At this condition, the voltage between drain and gate became large and made the oxide soft breakdown happen. The load-pull system is used to set up the measurement for optimized input and output power matching networks. The shift of the optimum load impedance and constant power-gain circles for power match indicated that the parameters of the stressed cells were changed by the damage in the gate oxide. The signal distortion, gate voltage swing, and thermal effect were all considered in this paper. The cells were fabricated by a 0.18-μm CMOS process. All of the characteristics of the devices were measured at 5.2 GHz.

Broadband and Low-Loss 1 : 9 Transmission-Line Transformer in 0.18- $\mu\hbox{m}$ CMOS Process

This letter proposes a transmission-line transformer (TLT) with high impedance-transformation ratio of 1 : 9 for wideband power amplifier design. The 1 : 9 TLT is realized with broadside-coupled and multiple-metal stacked transmission lines and achieves a broadband impedance transformation from 5.0 ±0.1Ω optimal load impedance of the power cell to 50-Ω load with a bandwidth of 4.4 to 6.6 GHz, which covers the required bandwidth of the IEEE 802.11a WLAN application. The measured minimum insertion loss is 1.07 dB at 5.8 GHz with a 3-dB bandwidth of 164%. This 1 : 9 TLT is fabricated in standard 0.18-μm CMOS process with a chip area of 426 μm × 589 μm including the test pad.

Design of a Highly Efficient 2–4-GHz Octave Bandwidth GaN-HEMT Power Amplifier

In this paper, the design, implementation, and experimental results of a high-efficiency wideband GaN-HEMT power amplifier are presented. A method based on source-pull/load-pull simulation has been used to find optimum source and load impedances across the bandwidth and then used with a systematic approach to design wideband matching networks. Large-signal measurement results show that, across 1.9-4.3 GHz, 9-11-dB power gain and 57%-72% drain efficiency are obtained while the corresponding power-added efficiency (PAE) is 50%-62%. Moreover, an output power higher than 10 W is maintained over the band. Linearized modulated measurements using a 20-MHz long-term evolution signal with 11.2-dB peak-to-average ratio show an average PAE of 27% and 25%, an adjacent channel leakage ratio of -44 and -42 dBc at 2.5 and 3.5 GHz, respectively.

Tuning a resonant energy harvester using a generalized electrical load

A fundamental drawback of vibration-based energy harvesters is that they typically featurea resonant mass/spring mechanical system to amplify the small source vibrations; thelimited bandwidth of the mechanical amplifier restricts the effectiveness of the energyharvester considerably. By extending the range of input frequencies over which a vibrationenergy harvester can generate useful power, e.g. through adaptive tuning, it is not onlypossible to open up a wider range of applications, such as those where the source frequencychanges over time, but also possible to relax the requirements for precision manufacture orthe need for mechanical adjustment in situ. In this paper, a vibration-based energyharvester connected to a generalized electrical load (containing both real and reactiveimpedance) is presented. It is demonstrated that the reactive component of theelectrical load can be used to tune the harvester system to significantly increase theoutput power away from the resonant peak of the device. An analytical modelof the system is developed, which includes non-ideal components arising fromthe physical implementation, and the results are confirmed by experiment. The − 3 dB (half-power) bandwidth of the prototype energy harvester is shown to be over threetimes greater when presented with an optimized load impedance compared to that for thesame harvester presented with an optimized resistive only load.

Design of a Class F Power Amplifier

A Class F power amplifier (PA) at 2.5GHz has been designed and fabricated. Test results show 15.7dB gain with 75.75% power added efficiency ( PAE), at an input level of 25dBm. The design procedure is presented, with various issues illustrated and addressed. A new method is proposed to obtain the optimum load and source impedances without iterations, which would usually be necessary.

Large-signal analysis of substrate effects in RF-power SOI-LDMOS transistors

Large-signal analysis of RF-power SOI-LDMOS transistors has been done on devices with different substrates resistivities. The effect of substrate resistivity on efficiency and output power has been investigated in class-AB operation and especially the loss mechanisms are studied. The large-signal performance is compared with the small-signal performance in an attempt to couple those parameters more tightly to each other. It is shown that the resistivity has great impact on the efficiency of the devices and the differences are related to losses in the substrate. The result verifies earlier indications that either a very high or very low substrate resistivity is beneficial to minimize the substrate losses. The study also shows interesting connections between the small-signal output resistance and capacitance and their large-signal counterparts derived from optimum load impedances.

Vibration Energy Harvesting with PZT Micro Device

A micro power generator harvesting vibration energy by resonant inertial oscillation of a piezoelectric laminated cantilever with proof mass was designed, fabricated, and characterized. The active part with 2 µm thick PZT on 5 µm silicon was equipped with interdigitated electrodes to achieve higher voltages. A coupling constant k2=5% was derived from the difference in resonance frequencies at low and high impedance. At optimal load impedance, a voltage of 1.6 V and an output power of 1.4 µW was measured with a 0.8x1.2 mm cantilever having an active area of 0.8x0.4 mm, excited with 2g at 870 Hz.

Uncoupled Impedance Matching for Capacity Maximization of Compact MIMO Arrays

We extend the study of Fei (IEEE Transactions on Antennas and Propagation, vol. 56, no. 11, pp. 35663575, Nov. 2008) on single-port matching impedance for capacity maximization in compact 2 × 2 multiple-input-multiple-output (MIMO) systems to N × N MIMO systems. In addition, we increase the degrees of freedom of the uncoupled matching where each port is terminated by an arbitrary load impedance. By maximizing an upper bound of the ergodic capacity for a N × N MIMO system with coupling at the receivers in high signal-to-noise ratio (SNR) scheme, a set of equations is formulated to find the optimized load impedance matrix. Input impedance match is proved to be an optimum solution when the MIMO system operates in high SNR scenarios. For three-element arrays, we show numerically that a significant performance improvement can be achieved by introducing input impedance matching. Observations suggest that the achieved improvement varies with array geometry, antenna spacing, and SNR.

Radioisotope Thin-Film Fueled Microfabricated Reciprocating Electromechanical Power Generator

A radioisotope power generator with a potential lifetime of decades is demonstrated by employing a 100.3-year half-lifetime 63Ni radioisotope thin-film source to electrostatically actuate and cause reciprocation in a microfabricated piezoelectric unimorph cantilever. The radioisotope direct-charged electrostatic actuation of the piezoelectric unimorph cantilever results in the conversion of radiation energy into mechanical energy stored in the strained unimorph cantilever. The gradual accumulation of the actuation charges leads to the pull-in of the unimorph cantilever into the radioisotope thin-film, and the resulting discharge leads to vibrations in the unimorph cantilever. During the vibrations, the stored mechanical energy is converted into electrical energy by the piezoelectric thin-film. The generator was realized by using both microfabricated lead zirconate titanate oxide-silicon (PZT-Si) and aluminum nitride-silicon (AIN-Si) unimorph cantilevers. The radioisotope direct-charged electrostatic actuation of the AIN-Si unimorph cantilevers by a 2.9-mCi 63Ni thin-film radiating 0.3 muW led to charge-discharge-vibrate cycles that resulted in the generation of 0.25% duty cycle 12.95-muW power pulses (across an optimal load impedance of 521 kOmega) at an overall energy conversion efficiency of 3.97%. These electrical power pulses can potentially be useful for periodically sampling sensor microsystems.

Comparative study of the Genetic Algorithms and Hessians Method for Minimization of the Electric Power Production Cost

Abstract — In this paper, we present a comparative study of the genetic algorithms and Hessian’s methods for optimal research of the active powers in an electric network of power. The objective function which is the performance index of production of electrical energy is minimized by satisfying the constraints of the equality type and inequality type initially by the Hessian’s methods and in the second time by the genetic Algorithms. The results found by the application of AG for the minimization of the electric production costs of power are very encouraging. The algorithms seem to be an effective technique to solve a great number of problems and which are in constant evolution. Nevertheless it should be specified that the traditional binary representation used for the genetic algorithms creates problems of optimization of management of the large-sized networks with high numerical precision. Keywords — Genetic algorithm, Flow of optimum load impedances, Hessians method, Optimal distribution.

Load–Pull Characterization Using Different Digitally Modulated Stimuli

A large-signal fully automated load-pull system for characterization of wireless communication systems dependant on digitally modulated signals is described. Load-pull measurements are used to determine optimum load impedances for power gain and adjacent-channel power ratio (ACPR) in a laterally-diffused metal oxide semiconductor stimulated with wideband code division multiple access and orthogonal frequency-division multiplexing signals of various peak-to-average ratios. The results are compared to load-pull measurements of gain and third-order intermodulated products (IMD3), based on a two-tone source signal. The results indicate that the optimum match impedance changes depending on whether a two-tone or a digitally modulated source is used as a stimulus. Furthermore, it is shown that the optimum load impedance for power gain and ACPR is also dependant on the desired output power the device. It is shown, that the change in the optimum load match for the different types of signals is significant enough to warrant further investigation

A 20 dBm Linear RF Power Amplifier Using Stacked Silicon-on-Sapphire MOSFETs

In this letter, a fully integrated 20-dBm RF power amplifier (PA) is presented using 0.25-mum-gate silicon-on-sapphire metal-oxide-semiconductor field-effect transistors (MOSFETs). To overcome the low breakdown voltage limit of MOSFETs, a stacked FET structure is employed, where transistors are connected in series so that each output voltage swing is added in phase. By using triple-stacked FETs, the optimum load impedance for a 20-dBm PA increases to 50Omega, which is nine times higher than that of parallel FET topology for the same output power. Measurement of a single-stage linear PA shows small-signal gain of 17.1 dB and saturated output power of 21.0dBm with power added efficiency (PAE) of 44.0% at 1.88 GHz. With an IS-95 code division multiple access modulated signal, the PA shows an average output power of 16.3 dBm and PAE of 18.7% with adjacent channel power ratio below -42dBc

RF Class-D Amplification With Bandpass Sigma–Delta Modulator Drive Signals

The power efficiency of a RF Class-D amplifier with a bandpass sigma-delta (SigmaDeltaM) modulator is analyzed for a complementary voltage-switched configuration. The modulator broadens the application of the amplifier to include signals with time varying envelopes such as W-CDMA. The addition of a modulator introduces new design variables which affect amplifier power efficiency including coding efficiency and the average transition frequency of the pulse train. Design equations are derived for the optimum load impedance, output power, conduction losses, capacitive switching losses, and drain efficiency. The general design equations are consistent with both periodic and aperiodic drive signals. Analytic and simulated results are compared for an example design with pseudomorphic high-electron mobility transistor and metal-semiconductor field-effect transistor switches with a fourth-order bandpass SigmaDeltaM. The results show a drain efficiency of 52% with a 10-dB peak-to-average power ratio W-CDMA source signal at a frequency of 500 MHz

리플렉터 형태의 K-대역 주파수 체배기 구현에 관한 연구

본 논문에서는 고주파 특성이 우수한 NEC사의 ne71300-N MESFET를 이용하여 24GHz 대역 국부발진기용 주파수 체배기를 설계 및 제작하였다. 멀티하모닉 로드 풀 시뮬레이션을 통하여 최적의 고조파 소스ㆍ부하 임피던스를 선택하였다. 리플렉터를 이용하여 변환 이득을 개선할 수 있었고, 대역저지필터를 이용하여 기본파와 3차 고조파 성분을 억제하였다. 측정한 결과 0 dBm의 입력신호에 대해 출력주파수인 24Ghz에서의 출력 전력은 -3.776dBm이고, 변환 이득은 0.736 dBm, 41.064 dBc의 높은 고조파 억압 특성을 얻었다. In this paper, a reflector type frequency doubler for local oscillator at 24GHz is designed and fabricated with ne71300-N MESFET. Optimum source and load impedances are decided through a multiharmonic load pull simulation technique. A conversion gain can be improved using the reflector and fundamental and third harmonics are well suppressed with open stub of <TEX>$\lambda$</TEX>/4 length Measured results show output power at 0dBm of input power is -3.776dBm, conversion gain 0.736dB, harmonic suppression 41.064dBc, respectively.

AlGaN/GaN HFET power amplifier integrated with microstrip antenna for RF front-end applications

A high-efficiency and compact AlGaN/GaN heterojunction field-effect transistor (HFET) power amplifier integrated with a microstrip antenna at 7.25 GHz is presented for RF front-end circuit applications. A microstrip circular sector antenna is employed as both a radiator and frequency-dependent output load. Higher order harmonics from the HFET in nonlinear operation are reactively terminated because of the harmonic termination characteristic of the antenna. Based on the optimum load impedance measured by a load-pull measurement setup, the AlGaN/GaN HFET power amplifier has been designed and fabricated at 7.25 GHz using the active integrated antenna concept. In this design approach, the measured antenna impedance is directly transformed to the optimum load impedance for maximum efficiency. The power amplifier with 1-mm gate periphery shows 42% peak power-added efficiency and 30.3-dBm saturated output power with a linear gain of 8 dB, which is in reasonably good agreement with measured discrete HFET load-pull data. Due to the antenna's characteristics, better than 30-dB harmonic suppression has been achieved at both the second and third harmonic frequencies in both the E- and H-planes. To the authors' best knowledge, this is the first demonstration of a high-frequency AlGaN/GaN HFET power amplifier integrated with an antenna.

Watt-level Ka- and Q-band MMIC power amplifiers operating at low voltages

Ka- and Q-band watt-level monolithic power amplifiers (PAs) operating at a low drain bias of 3.6 V are presented in this paper. Design considerations for low-voltage operation have been carefully studied, with an emphasis on the effect of device models. The deficiency of conventional table-based models for low-voltage operation is identified. A new nonlinear device model, which combines the advantages of conventional analytical models and table-based models, has been developed to circumvent the numerical problems and, thus, to predict optimum load impedance accurately. The model was verified with load-pull measurements at 39 GHz. To implement a low-voltage 1-W monolithic-microwave integrated-circuit amplifier, careful circuit design has been performed using this model. A Q-band two-stage amplifier showed 1-W output power with a high power gain of 15 dB at 3.6-V drain bias. The peak power-added efficiency (PAE) was 28.5% and 1-dB compression power (P/sub 1 dB/) was 29.7 dBm. A Ka-band two-stage amplifier showed a P/sub 1 dB/ of 30 dBm with 24.5-dB associated gain and 32.5% PAE. Under very low dc power conditions (P/sub dc/<2 W, V/sub ds/=3.4 V), the amplifiers showed 29-dBm output power and PAE close to 36%, demonstrating ultimate low-power operation capability. To the best of our knowledge, this is the first demonstration of watt-level PA's under 3.6-V operation at 26 and 40 GHz. Compared with the published data, this work also represents state-of-the-art performance in terms of power gain, efficiency, and chip size.