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Active gate driving of power devices seeks to shape switching trajectories via the gate, for example, to reduce EMI without degrading efficiency. To this end, driver ICs with integrated arbitrary waveform generators have been used to achieve complex gate signals. This article describes, for the first time, the implementation details of a digitally programmable arbitrary waveform gate driver capable of a 10-GHz waypoint rate, including comprehensive design considerations for critical high-speed subsystems that codify the tradeoff in flexibility, speed, and area. The design, which is taped out in a 180-nm high-voltage CMOS process, utilizes buffers that switch up to ten times in a single clock cycle to overcome the limited achievable clock speed of high-voltage silicon integrated circuits and a fully digital architecture to provide robustness under high slew rates of the ground rail. The driver IC has networks of 100-ps delay elements that are configured prior to a switching transient, to selectively control an array of fast, parallel-connected drivers with different output impedances. Key to the high timing resolution are high-speed asynchronous circuits for memory readout, output buffering, and pulse generation. The driver IC is experimentally evaluated to have a 100-ps resolution and to operate reliably in a 400-V gallium nitride (GaN) bridge leg, under ground-rail voltage slew rates peaking at over 100 V/ns. Design rules are provided to obtain an architecture with the least area for a given set of timing and impedance resolution requirements. The reported design methods enable complex driving waveforms to be applied during nanosecond-scale transients of GaN power devices and demonstrate how digitally programmable active gate drivers for GaN power FETs can be designed to meet a given set of application requirements. [ABSTRACT FROM AUTHOR]

Power semiconductor devices have maximum junction temperature limits, but it is not straightforward to sense or infer temperature inside sealed devices in running converters. One method is to observe electrical behavior that is known to be temperature dependent. For example, in some gallium nitride (GaN) power semiconductor devices, the maximum slope of the device current at turn-on has been shown to reduce as the junction temperature increases. This article demonstrates the first noncontact overtemperature protection circuit for GaN power devices that exploits this effect and overcomes the complication that this inverse proportionality is affected by load current. A variant of a previously reported magnetic field “Infinity Sensor,” named after its figure-of-eight topology and high bandwidth (>200 MHz), measures di/dt. Using the sensor signal as the only input, a detection circuit finds peak di/dt, and a high-speed integrator derives instantaneous load current. The reference voltage for the decision-making part of the circuit is automatically adjusted as a function of load current, in order to counteract the dependence of di/dt on load current. Experimental results on a 400 V, 2 kW buck converter show the protection circuit successfully activating within ±5 °C of a preprogrammed junction temperature setting, independently of load current, for settings of 100, 120, and 140 °C. [ABSTRACT FROM AUTHOR]

This paper reports the application of silicon bipolar junction transistor (BJT) modeling techniques to the modeling of dynamic behavior of high-voltage 4H-SiC BJTs, and the experimental validation thereof. High-voltage silicon BJTs are impractical due to their low current gain that requires a bulky base driver. Emergence of high-voltage 4H-SiC vertical NPN BJTs with a tenfold higher gain enables the application of efficient drivers, with ratings close to those of IGBTs. This paper demonstrates the advantages offered by 4H-SiC BJTs by means of wide-scale measurements at 800 V and 10 A in a range of temperatures up to 175 °C and adjusted base driver switching rates. This paper shows that the turn-off storage delay in the SiC BJT is two orders of magnitude lower than that of the silicon device. It also shows that the turn-on switching transients of SiC device are by an order of magnitude and the turn-off transients are by two orders of magnitude faster than that of its silicon counterpart, resulting in a tenfold reduction of the switching energy. It also demonstrates the temperature dependence of switching transients of the silicon BJT, and the relative temperature-invariance of the SiC device's performance. This paper concludes with validation of the transient models for the 4H-SiC NPN BJT, showing that the model is sufficiently accurate for transient switching and loss calculations. [ABSTRACT FROM AUTHOR]

Most power electronic circuits naturally suffer from undesirable oscillations, which increase circuit stress and electromagnetic interference. These oscillations can, for example, arise from commutation cell resonance, and are particularly problematic in fast-switching SiC and GaN circuits. Damping these oscillations by active gate driving has been previously proposed as an alternative to limiting the switching speed or further minimizing parasitic inductance. However, for active drivers with almost unlimited degrees of freedom in the choice of gate driving profiles, fast and efficient profile optimization techniques have yet to be developed. This letter analytically determines four key measurable indicators, which help to find optimal gate signal shaping settings for an active driver. These include the device voltage gradient, as well as the gradient and overshoot level at specific points in the transient current. This optimization strategy is tested by using it to find the optimal settings for a variable-resistance active gate driver in a 400V-GaN boost converter. Measurements of switching transients and radiated electromagnetic emissions show experimentally that the proposed strategy reduces noise and switching loss at the same time. Compared to slower nonactive driving, radiated electromagnetic emissions are down by 10 dB, and losses by 6%. [ABSTRACT FROM AUTHOR]

A highly efficient 5-kW bidirectional dc–dc converter power stage operating from a 400-V supply implementing super-junction (SJ) metal–oxide–semiconductor field-effect transistor (MOSFETs) is presented. SJ MOSFETs have low on-state resistances and low switching losses. However, their application in voltage-source converters can be compromised by the reverse recovery behavior of their intrinsic diodes and their highly nonlinear output capacitances. A series switching-aid circuit is used to control the output capacitance charging current. The dead times between switching transitions are assessed and optimized in order to deactivate the intrinsic diodes. The combination of these techniques enables very high efficiencies to be attained. Calorimetric measurements indicate a full-load efficiency of 99.1% for the prototype 5-kW dc–dc converter power stage. A loss reduction of approximately 50% is achieved with the prototype converter power stage when compared to an equivalent insulated-gate bipolar transistor (IGBT)-based power stage. Lastly, a loss versus duty cycle function is experimentally determined, which can be used to inform the design of a maximum efficiency point tracking system. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive evaluation of fabrication techniques for the integration of coils into textiles, for the purpose of enabling low-power wireless power transfer; for example, the powering of on-body monitoring devices, such as heart-rate monitors. Key electrical parameters of the coils required to maximize power transfer efficiency are identified from theory. Flexible coils have been fabricated using standard processes widely used in the textile industry, such as screen printing and embroidery. The screen printed coils were fabricated with a silver-polymer ink on a printed interface layer; the embroidered coils were fabricated using a variety of conductive threads formed by coating textile fibers and through the use of copper fibers. These coils have been experimentally characterized and evaluated for use in wireless power transfer applications. The effects of coil geometry and separation on the dc–dc power transfer efficiency using Qi standard compliant driver and receiver circuits are reported. [ABSTRACT FROM PUBLISHER]

Active gate driving has been demonstrated to beneficially shape switching waveforms in Si- and SiC-based power converters. For faster GaN power devices with sub-10-ns switching transients, however, reported variable gate driving has so far been limited to altering a single drive parameter once per switching event, either during or outside of the transient. This paper demonstrates a gate driver with a timing resolution and range of output resistance levels that surpass those of existing gate drivers or arbitrary waveform generators. It is shown to permit active gate driving with a bandwidth that is high enough to shape a GaN switching during the transient. The programmable gate driver has integrated high-speed memory, control logic, and multiple parallel output stages. During switching transients, the gate driver can activate a near-arbitrary sequence of pull-up or pull-down output resistances between 0.12 and 64 Ω. A hybrid of clocked and asynchronous control logic with 150-ps delay elements achieves an effective resistance update rate of 6.7 GHz during switching events. This active gate driver is evaluated in a 1-MHz bridge-leg converter using EPC2015 GaN FETs. The results show that aggressive manipulation of the gate-drive resistance at sub-nanosecond resolutions can profile gate waveforms of the GaN FET, thereby beneficially shaping the switch-node voltage waveform in the power circuit. Examples of open-loop active gate driving are demonstrated that maintain the low switching loss of constant-strength gate driving, while reducing overshoot, oscillation, and EMI-generating high-frequency spectral content. [ABSTRACT FROM PUBLISHER]

This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art. [ABSTRACT FROM PUBLISHER]

A new design method for producing high-performance and power-rail slew-tolerant floating-voltage level shifters is presented, offering increased speed, reduced power consumption, and smaller layout area compared with previous designs. The method uses an energy-saving pulse-triggered input, a high-bandwidth current mirror, and a simple full latch composed of two inverters. A number of optimizations are explored in detail, resulting in a presented design with a dVdd/{dt} slew immunity of 30 V/ns, and near-zero static power dissipation in a 180-nm technology. Experimental results show a delay of below 370 ps for a level-shift range of 8–20 V. Postlayout simulation puts the energy consumption at 2.6 pJ/bit at 4 V and 7.2 pJ/bit at 20 V, with near symmetric rise and fall delays. [ABSTRACT FROM PUBLISHER]

Silicon carbide (SiC) switching power devices (MOSFETs, JFETs) of 1200 V rating are now commercially available, and in conjunction with SiC diodes, they offer substantially reduced switching losses relative to silicon (Si) insulated gate bipolar transistors (IGBTs) paired with fast-recovery diodes. Low-voltage industrial variable-speed drives are a key application for 1200 V devices, and there is great interest in the replacement of the Si IGBTs and diodes that presently dominate in this application with SiC-based devices. However, much of the performance benefit of SiC-based devices is due to their increased switching speeds ( di/dt, dv/ dt), which raises the issues of increased electromagnetic interference (EMI) generation and detrimental effects on the reliability of inverter-fed electrical machines. In this paper, the tradeoff between switching losses and the high-frequency spectral amplitude of the device switching waveforms is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. While exploiting the full switching-speed capability of SiC-based devices results in significantly increased EMI generation, the all-SiC combination provides a 70% reduction in switching losses relative to all-Si when operated at comparable dv/dt. It is also shown that the loss-EMI tradeoff obtained with the Si-SiC device combination can be significantly improved by driving the IGBT with a modified gate voltage profile. [ABSTRACT FROM AUTHOR]

This paper describes the design and operation of power conditioning system with maximum power transfer tracking (MPTT) for low-power electromagnetic energy harvesters. The system is fully autonomous, starts up from zero stored energy, and actively rectifies and boosts the harvester voltage. The power conditioning system is able to operate the harvester at the maximum power point against varying excitation and load conditions, resulting in significantly increased power generation when the load current waveform has a high peak-to-mean ratio. First, the paper sets out the argument for MPTT, alongside the discussion on the dynamic effects of varying electrical damping on the mechanical structure. With sources featuring stored energy, such as a resonant harvester, maximum power point control can become unstable in certain conditions, and thus, a method to determine the maximum rate of change of electrical damping is presented. The complete power conditioning circuit is tested with an electromagnetic energy harvester that generates 600 mV rms ac output at 870 μW under optimum load conditions, at 3.75 m·s-2 excitation. The digital MPTT control circuit is shown to successfully track the optimum operating conditions, responding to changes in both excitation and the load conditions. At 2 V dc output, the total current consumption of the combined ancillary and control circuits is just 22 μA. The power conditioning system is capable of transferring up to 70% of the potentially extractable power to the energy storage. [ABSTRACT FROM AUTHOR]

In this paper, a complete power conditioning system for a vibration energy harvester is presented that operates at ultralow power levels. The power conditioning system, implemented with discrete components, is self-starting and fully autonomous, and based upon a full-wave boost rectifier topology. The design utilizes the stray inductance of the harvester's coil, eliminating the need for separate inductors, and employs open-loop control that reduces the quiescent power overhead to just 21 μW, while still extracting 84% of the maximum available power from the harvester. The design of the subsystems, including self-start circuitry, is described in detail, and it is shown that careful active device selection is required to minimize losses. It is experimentally demonstrated that the power converter achieves conversion efficiencies of up to 76% at submilliwatt power levels, including quiescent losses. The overall system efficiency peaks at 65% at 0.9 mW, while still achieving 51% at 200 μW. The ability of this system to operate efficiently at ultralow average power levels opens up new possibilities to further miniaturize vibration harvesters and deploy them into environments with lower vibration levels than is currently possible. [ABSTRACT FROM PUBLISHER]

Consideration of the higher order time derivatives of voltage and current transitions in power semiconductor devices enables the specification of “S-shaped” switching waveforms which offer an improved tradeoff between high-frequency EMI generation and switching losses. In comparison with the widely used first-order derivative trapezoidal switching waveform approximation, Fourier analysis of the proposed “S-shaped” waveform shows that it exhibits a 20 dB/dec steeper spectral gradient at high frequencies, resulting in a 20 dB greater reduction in high-frequency spectral content per decade increase in rise time. Numerical analysis of the proposed waveform shows that both peak and total RF power, employed as indicative EMI metrics, are reduced significantly with no increase in overall switching time. Experimental investigation of the effect of introducing a frequency-selective EMI transmission path shows that the overall trends in the relationships between time-domain waveform parameters and high-frequency spectral content are maintained, while the values of the waveform timing parameters which minimize the two EMI metrics are changed. [ABSTRACT FROM AUTHOR]

For various medical monitoring and sensing applications it is desirable to power the electronics by scavenging energy from any locally available source. An electrostatic motion-driven generator for low-frequency (human body) motion has been developed by the authors using microelecromechanical system technology. The prototype generates pulses of 250 V on a 10-pF capacitor. This paper examines the design of a circuit and semiconductor devices to convert this energy to a low voltage. Because of the very small charge involved, the effects of leakage and parasitic stored charge are important. Converters for this application using silicon-on-insulator metal-oxide-semiconductor field-effect transistors and insulated gate bipolar transistors are compared using physics-based finite-element simulation. The overall effectiveness of the generation process is shown to be composed of several terms which are functions of system parameters such as generator flight time, semiconductor device area, and circuit inductance. It is shown that device area is a compromise between leakage current, charge storage, and on-state voltage. It can, for a given generator and inductance, be optimized to provide the maximum energy yield. Parasitic series inductance is shown to be of little importance to the circuit efficiency; however, parasitic capacitance has a significant influence. [ABSTRACT FROM AUTHOR]

An inertial generator based on a moving-plate capacitor can provide energy for medical sensors from low-frequency (human body) motion. The energy exists as a very small charge (4 nC) at high voltage (300 V). An initial proposal for power processing used a carefully scaled lateral power MOSFET-diode pair, which results in a low, but sufficient, energy yield. It was found that increasing the area of the MOSFET to reduce conduction loss is highly detrimental to the energy yield because of capacitive loading of the generator. This paper examines alternative device topologies which may greatly increase the energy yield for a given system size by increasing both the generation efficiency and the conversion efficiency. An insulated gate bipolar transistors (IGET) and a MOS-triggered thyristor, both based on previous silicon-on-insulator MOSFET designs, are examined for their switching speed and losses using physics-based finite-element simulation. The scaling criteria to achieve optimum system effectiveness are discussed. The small charge available from the generator results in a brief conduction period which does not allow the devices to reach their steady-state carrier distributions. Nevertheless the IGBT, and especially the MOS-triggered thyristor, switch on faster than the MOSFET, run at higher current densities, and provide improved efficiency. This allows the devices to be reduced in area leading to less capacitive loading on the generator. It also allows a reduction in the value and volume of the circuit inductor without a onduction loss penalty. We describe the device behavior in detail for the various phases of the conversion cycle and illustrate device/circuit tradeoffs graphically. Requirements are outlined for the development of power devices for microgenerators in implanted medical sensors. [ABSTRACT FROM AUTHOR]