Diode Junction Capacitance Research Articles

Impact of Current on the Parallel Resistance and Junction Capacitance of Light-Emitting Diodes

Impact of Current on the Parallel Resistance and Junction Capacitance of Light-Emitting Diodes

Accurately Modeling Zero-Bias Diode-Based RF Power Harvesters With Wide Adaptability to Frequency and Power

This paper proposes an analytical method for effectively evaluating the performances of zero-bias diode-based RF power harvesters. The method allows the accurate calculation of both the diode power conversion efficiency (PCE) and matching efficiency, while showing the wide adaptability to frequency and input power. To calculate the diode PCE accurately, the junction voltage is built based on modeling the diode junction capacitance and turn-on voltage. Using the accurate diode PCE, the equivalent nonlinear resistance of the diode is calculated, and thus the diode impedance is obtained. This helps to design a matching network with required bandwidths and evaluate the corresponding matching efficiency. The total PCE of the RF power harvester is finally obtained by multiplying the diode PCE and matching efficiency. For verification, dual-band RF power harvesters based on diodes of SMS7630 and HSMS-2850 are developed to cover the two 5G frequency bands for three telecom operators in China (2.515-2.675, 3.4-3.5 & 3.5-3.6 GHz). They are designed to operate in the low power range of −25-−5 dBm for low power harvesting scenarios. Compared with the simulated results, the calculation discrepancy of less than 3.12% can be achieved in evaluating the total PCEs of the RF power harvesters. Prototypes of the designed RF power harvesters were fabricated and measured for validation. It shows that the proposed analytical method can provide design guidelines for developing a multi-band RF power harvester.

Analysis of a Hybrid Variable-Frequency-Duty-Cycle-Modulated Low-$Q$ $LLC$ Resonant Converter for Improving the Light-Load Efficiency for a Wide Input Voltage Range

Light load efficiency and output voltage regulation of alow-Q LLC resonant converter is a critical problem for wide input voltage and load range applications. Parasitic capacitances such as rectifier diode junction capacitance (C3) degrade the soft switching performance. Compact size, high density, and high transformer turns-ratio requirements for microinverter applications add significant distributed capacitance (Cd) of the low-profile transformer, worsening the output regulation and zero-voltage-switching (ZVS) capability at light loads. Wide switching frequency requirement for regulation at light loads, which increases core losses and turnOFF switching losses in power MOSFETs, further degrades the power conversion efficiency. The conventional phase-shift modulation causes a high circulating current and loss of ZVS at light loads. Therefore, a hybrid adjustable switching-frequency-dutycycle modulation technique for improving the light load efficiency is proposed and analyzed for a full-bridge LLC resonant converter. Accurate loss analysis for the proposed modulation scheme, including the effect of parasitic capacitances, is performed using time-domain equations. The proposed methodology precalculates the optimal duty cycle at light load conditions for the required input voltage range such that minimum power losses are incurred. Variation in switching frequency at the preselected duty-cycle value regulates the output voltage. ZVS over a wide range of operating conditions is observed. An experimental prototype for a 20-40 V input, 380-V/300-W output LLC converter is tested for the validation of theoretical analysis.

A Family of Zero-Voltage-Switched Resonant Converters: Derivation, Operation, and Design

Soft switching based on resonant operation, through mitigating switching loss and alleviating electromagnetic interference, is essential to high-frequency operation to achieve high power density. To overcome the obstacles of high switch voltage stress and ease the contradiction between voltage stress and conduction loss for traditional single-switch resonant converters, a family of zero-voltage-switched (ZVS) isolated resonant converters is proposed which utilizes a novel resonant switch. The converters enable parasitic components, including transformer leakage inductance, switch output capacitance, and diode junction capacitance to act as a part of resonant components, which facilitates ZVS and zero-current-switching operation and pushes up switching frequency. The specific derivation of the topologies is expounded, and one of the proposed converters is taken for example to perform in-depth analysis, whose mode analysis, operation principles, and parameter design method are minutely presented. Synchronous rectification is employed to further improve efficiency. A prototype was built in the laboratory and the experimental results validate the theoretical analysis well.

Air Stable Indium-Gallium-Zinc-Oxide Diodes With a 6.4 GHz Extrinsic Cutoff Frequency Fabricated Using Adhesion Lithography

High speed rectifiers that can be fabricated at low cost whilst still maintaining a high performance are of interest for wireless communication applications. In this letter amorphous indium gallium zinc oxide (a-IGZO) has been used with adhesion lithography (a technique to create asymmetric planar electrodes separated by a nanogap) to fabricate high performance Schottky diode rectifiers. The diode area and junction capacitance can be significantly reduced using this technique, improving device cut-off frequencies. Devices of different widths have been fabricated showing rectification ratios between 103-104. Capacitances measured for devices of various sizes were all on the order of 0.1 pF. By applying ac signals to the diode and measuring the output voltage across a load resistor a cut-off frequency was found. a-IGZO diodes with an extrinsic cut-off frequency of 6.4 GHz at a 15 dBM input power have been realized. The devices also show good air stability with little change in current-voltage characteristics after 12 months.

Full-Bridge+SRT Hybrid DC/DC Converter for a 6.6-kW EV On-Board Charger

This paper suggests a hybrid pulsewidth-modulation (PWM) dc/dc converter for an electric vehicle (EV) on-board charger (OBC). It is composed of a full-bridge (FB) converter and a resonant converter with secondary resonance tank (SRT). They are coupled in a single transformer so that any power distribution problem that causes a size increase in the transformer can be solved. Dual power flow of the proposed charger provides an increase in charger gain and a reduction of turn-off voltage spikes of the rectifying diodes caused by transformer leakage inductance and diode junction capacitance. These characteristics help reduce diode loss and remove dissipative snubber circuitry. In addition, this structure has the additional advantage of output inductor size due to the reduction of voltage variation applied to the inductor. The feasibility of the proposed charger is verified with a 6.6-kW prototype implemented by a design procedure.

Read Challenges in Crossbar Memories With Nanoscale Bidirectional Diodes and ReRAM Devices

This paper presents a simulation based study of the impact of nanoscale bidirectional diode reverse saturation current, junction capacitance, and crossbar coupling capacitances on the read operation of nanoscale ReRAM devices in 1Diode 1ReRAM crossbar memory architectures. Our results show that the maximum achievable crossbar memory density is a strong function of the diode reverse saturation current, which governs the sneak current in steady-state read mode. For read operations with ultrafast read voltage pulses, additional sneak paths due to diode junction capacitances and line-to-line coupling capacitances in crossbar arrays come into the picture. This causes transient spike in the read current, which can adversely affect the read energy and permissible read time. The overshoot in read current worsens as the size of crossbar arrays increases. The simulation studies presented here provides an in-depth understanding of these issues and its implications on resistive crossbar arrays.

The Impact of Nonlinear Junction Capacitance on Switching Transient and Its Modeling for SiC MOSFET

The nonlinear junction capacitances of power devices are critical for the switching transient, which should be fully considered in the modeling and transient analysis, especially for high-frequency applications. The silicon carbide (SiC) MOSFET combined with SiC Schottky Barrier Diode (SBD) is recognized as the proposed choice for high-power and high-frequency converters. However, in the existing SiC MOSFET models only the nonlinearity of gate-drain capacitance is considered meticulously, but the drain–source capacitance, which affects the switching commutation process significantly, is generally regarded as constant. In addition, the nonlinearity of diode junction capacitance is neglected in some simplified analysis. Experiments show that without full consideration of nonlinear junction capacitances, some significant deviations between simulated and measured results will emerge in the switching waveforms. In this paper, the nonlinear characteristics of drain–source capacitance in SiC MOSFET are studied in detail, and the simplified modeling methods for engineering applications are presented. On this basis, the SiC MOSFET model is improved and the simulation results with improved model correspond with the measured results much better than before, which verify the analysis and modeling.

An On-Chip Temperature Sensor With a Self-Discharging Diode in 32-nm SOI CMOS

We report a 39 μm × 27 μm on-chip temperature sensor which uses the temperature-dependent reverse-bias leakage current of a lateral silicon on insulator (SOI) CMOS p-n diode to monitor the thermal profile of a 32-nm microprocessor core. In this sensor, the diode junction capacitance is first charged to a fixed voltage. Subsequently, the diode capacitance is allowed to self-discharge through its temperature-dependent reverse-bias current. Next, by using a time-to-digital-converter circuit, the discharge voltage is converted to a temperature-dependent time pulse, and finally, its width is measured by using a digital counter. This compact temperature sensor demonstrates a 3σ measurement inaccuracy of ±1.95°C across the 5°C-100°C temperature range while consuming only 100 μW from a single 1.65-V supply.

On Estimating and Canceling Parasitic Capacitance in Submillimeter-Wave Planar Schottky Diodes

The equivalent circuit model of a submillimeter planar diode is investigated. In particular, the parasitic finger to pad capacitance that shunts the diode junction severely degrades the performance of frequency multiplier. Therefore, precise estimation of its value is crucial to circuit design in the submillimeter wave range. In this letter, a parallel diode structure is analyzed, and symmetry is utilized to remove parasitic elements external to the finger loop. This analytical approach is verified through measurement on a 200 GHz planar diode circuit. To increase the diode junction capacitance modulation ratio, one possible solution is also suggested.

The nonlinear current behaviour of a driven R–L-Varactor in the low frequency range

The nonlinear behaviour of an R–L-Varactor circuit, simulated by Multisim 7.0 at a driving frequency that is below the circuit resonance frequency, is reported and evaluated. A new high amplitude oscillation is observed and attributed to the emergence of a large diode junction capacitance. Increasing the driving signal amplitude, the circuit is led to a non-periodic mode of operation, producing trajectories of increasing chaotic content in a four-dimensional phase space. At specific amplitudes a two-dimensional tori was monitored, where trajectories are periodic, like in a two oscillator system with commensurate frequencies. Poincaré cross-sections, FFT spectra and correlation dimension calculations, suggest the quasi-periodicity route to chaos.

On the Frequency Response Symmetry of Diode Mixers

A mixing process is symmetrical when the conversion loss and group delay are equal between a downconversion and the corresponding upconversion. It is shown here by measurement that diode mixers have some degree of response asymmetry. Simulations show that the response asymmetry is caused by the voltage-variable junction capacitance of the mixer diodes. The response asymmetry sets a limit on the accuracy of three-mixer and other techniques to derive the frequency response of individual mixers.

Automatic Tuned MRI RF Coil for Multinuclear Imaging of Small Animals at 3T

We have developed an MRI RF coil whose tuning can be adjusted automatically between 120 and 128 MHz for sequential spectroscopic imaging of hydrogen and fluorine nuclei at field strength 3 T. Variable capacitance (varactor) diodes were placed on each rung of an eight-leg low-pass birdcage coil to change the tuning frequency of the coil. The diode junction capacitance can be controlled by the amount of applied reverse bias voltage. Impedance matching was also done automatically by another pair of varactor diodes to obtain the maximum SNR at each frequency. The same bias voltage was applied to the tuning varactors on all rungs to avoid perturbations in the coil. A network analyzer was used to monitor matching and tuning of the coil. A Pentium PC controlled the analyzer through the GPIB bus. A code written in LABVIEW was used to communicate with the network analyzer and adjust the bias voltages of the varactors via D/A converters. Serially programmed D/A converter devices were used to apply the bias voltages to the varactors. Isolation amplifiers were used together with RF choke inductors to provide isolation between the RF coil and the DC bias lines. We acquired proton and fluorine images sequentially from a multicompartment phantom using the designed coil. Good matching and tuning were obtained at both resonance frequencies. The tuning and matching of the coil were changed from one resonance frequency to the other within 60 s.

An improved family of ZVS-PWM active-clamping DC-to-DC converters

A new family of DC-to-DC converters featuring clamping action, PWM modulation and soft-switching (ZVS) in both active and passive switches, is proposed to overcome the limitations of clamped mode DC-to-DC converters. The new family of converters is generated and the new circuits are presented. As the resonant circuits absorb all parasitic reactances, including transistor output capacitance and diode junction capacitance, these converters are suitable for high-frequency operation. Principle of operation of the boost converter, theoretical analysis, simulation and experimental results are presented, taken from a laboratory prototype rated at 1600 W, input voltage of 300 V, output voltage of 400 V, and operating at 100 kHz. The measured efficiency at full load was 98%.

Effects of nonlinear diode junction capacitance on the nose-to-nose calibration

We examine the effects of nonlinear diode junction capacitance on the fundamental premise of the nose-to-nose calibration, that the kickout pulse is identical in shape and duration to the impulse response of a sampling circuit. We offer a physical explanation for the error introduced by the nonlinear junction capacitance using small-signal diode equations.

Photovoltaic-p-i-n diodes for RF control-switching application

A photovoltaic-p-i-n diode switch, consisting of two back-to-back p-i-n diodes which can be forward biased to the ON state by photovoltaic cell photocurrents, is introduced for optically controlling RF signals. Without light, the switch is in the OFF state and isolation is determined by the diode junction capacitance. We report a device operating in the VHF range and handling 25 W. With 40 mA photocurrent injected into each diode, the measured insertion loss at 25-W input power is /spl ap/0.08 dB, mainly limited by the diode series resistance; its capacitance was 380 fF. Experiments indicate that low insertion loss requires the signal period /spl Lt/ carrier lifetime so that carrier sweep out in the I-region does not reduce conductivity.

On the leading leg transition of phase-shifted ZVS-FB converters

The primary current drop during the leading leg transition of phase-shifted zero-voltage-switching full-bridge (ZVS-FB) power converters is investigated. It is shown that this phenomenon is affected by the junction capacitance of rectifier diodes and transformer winding capacitance.

A new class of pulsewidth-modulated multi-resonant converters using resonant inductor freewheeling

A new class of pulsewidth-modulated zero-voltage-switching multi-resonant converters (PWM-ZVS-MRCs) is presented. Instead of controlling the switching frequency, the output voltage is regulated by controlling the freewheeling period of the resonant inductor, while maintaining constant-frequency operation. This class of converter incorporates the advantages both of PWM converters and of their frequency-modulated counterparts (FM-ZVS-MRCs). Moreover, in contrast to their quasi-resonant counterparts, PWM-ZVS-QRCs, possible parasitic oscillations between the diode junction capacitance and the resonant inductor are eliminated. Simulation of a boost PWM-ZVS-MRC is presented and is verified by experimental results.

Cooled Schottky varactor frequency multipliers at submillimeter wavelengths

The efficiency of a Schottky varactor frequency multiplier at submillimeter wavelengths can be increased by cooling the diode. The increased mobility of the free carriers causes the series resistance to decrease, and the efficiency can increase as much as a few dB at low input power levels. At high output frequencies and at high power levels the efficiency of the multiplication is decreased by the current saturation, because the junction capacitance cannot be pumped effectively. When the diode is cooled, the maximum current of the diode increases and much more output power can be expected. There are also slight changes in the I-V characteristic and in the diode junction capacitance, but they have a negligible effect on the efficiency of the multiplier. The theoretical maximum output power near 1 THz is calculated to increase by about 10 dB from 50 mu W to 500 mu W, when the multiplier chain is cooled to 77 K. However, considerable improvement in the efficiency can be achieved by cooling to 150 K, which is easily attained in space by passive cooling.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Class E resonant low di/dt rectifier

An analysis and experimental verification of a Class E voltage-driven resonant low di/dt rectifier are given. The circuit contains two resonant components: an inductor and a capacitor. Design equations are derived using Fourier series techniques. A prototype of the rectifier was built and tested at 500 kHz and an output voltage of 5 V. The theoretical and experimental results were in good agreement. The rectifier offers soft switching of the diode, decreasing noise and switching losses. However, the diode junction capacitance and the resonant components form a detrimental resonant circuit during the diode off state, causing ringing superimposed on the desirable waveforms.