Syed K. Islam

Low-Voltage Bulk-Driven Operational Amplifier With Improved Transconductance

This paper presents two low-voltage bulk-driven amplifier input stages with enhanced transconductance. The idea is to introduce auxiliary differential pairs into a conventional bulk-driven stage to boost its transconductance. A low-voltage cascode biasing circuitry based on EKV models is also employed to ensure proper operation of the proposed input stages. An operational amplifier is then implemented with the proposed input stages and biasing circuits as its core building blocks and including a modified low-voltage class AB output amplifier to guarantee rail-to-rail output voltage range. The overall amplifier was implemented in a 0.35 μm n-well CMOS process using 1-V power supply. The measurement results show significant improvement in the performance of the operational amplifier compared to prior arts.

Effects of silicon carbide (SiC) power devices on HEV PWM inverter losses

The emergence of silicon carbide (SiC) based power semiconductor switches with their superior features compared with silicon (Si) based switches has resulted in substantial improvements in the performance of power electronics converter systems. These systems with SiC power devices are more compact, lighter, and more efficient, so they are ideal for high-voltage power electronics applications, including hybrid electric vehicle (HEV) traction drives. In this paper, the effect of SiC-based power devices on HEV traction drive losses are investigated. Reductions in heat sink size and device losses with the increase in the efficiency will be analyzed using an averaging model of a three-phase PWM inverter (TPPWMI). For more accurate results, device physics is taken into consideration to find the loss equations for the controllable switches.

Low-Power Low-Voltage Current Readout Circuit for Inductively Powered Implant System

Low voltage and low power are two key requirements for on-chip realization of wireless power and data telemetry for applications in biomedical sensor instrumentation. Batteryless operation and wireless telemetry facilitate robust, reliable, and longer lifetime of the implant unit. As an ongoing research work, this paper demonstrates a low-power low-voltage sensor readout circuit which could be easily powered up with an inductive link. This paper presents two versions of readout circuits that have been designed and fabricated in bulk complementary metal-oxide semiconductor (CMOS) processes. Either version can detect a sensor current in the range of 0.2 μA to 2 μA and generate square-wave data signal whose frequency is proportional to the sensor current. The first version of the circuit is fabricated in a 0.35-μ m CMOS process and it can generate an amplitude-shift-keying (ASK) signal while consuming 400 μ W of power with a 1.5-V power supply. Measurement results indicate that the ASK chip generates 76 Hz to 500 Hz frequency of a square-wave data signal for the specified sensor current range. The second version of the readout circuit is fabricated in a 0.5-μ m CMOS process and produces a frequency-shift-keying (FSK) signal while consuming 1.675 mW of power with a 2.5-V power supply. The generated data frequency from the FSK chip is 1 kHz and 9 kHz for the lowest and the highest sensor currents, respectively. Measurement results confirm the functionalities of both prototype schemes. The prototype circuit has potential applications in the monitoring of blood glucose level, lactate in the bloodstream, and pH or oxygen in a physiological system/environment.

A 200 °C Universal Gate Driver Integrated Circuit for Extreme Environment Applications

High-temperature power converters (dc-dc, dc-ac, etc.) have enormous potential in extreme environment applications, including automotive, aerospace, geothermal, nuclear, and well logging. For successful realization of such high-temperature power conversion modules, the associated control electronics also need to perform at high temperature. This paper presents a silicon-on-insulator (SOI) based high-temperature gate driver integrated circuit (IC) incorporating an on-chip low-power temperature sensor and demonstrating an improved peak output current drive over our previously reported work. This driver IC has been primarily designed for automotive applications, where the underhood temperature can reach 200 °C. This new gate driver prototype has been designed and implemented in a 0.8 μm, 2-poly, and 3-metal bipolar CMOS-DMOS (Double-Diffused Metal-Oxide Semiconductor) on SOI process and has been successfully tested for up to 200 °C ambient temperature driving a SiC MOSFET and a SiC normally-ON JFET. The salient feature of the proposed universal gate driver is its ability to drive power switches over a wide range of gate turn-ON voltages such as MOSFET (0 to 20 V), normally-OFF JFET (-7 to 3 V), and normally-ON JFET (-20 to 0 V). The measured peak output current capability of the driver is around 5 A and is thus capable of driving several power switches connected in parallel. An ultralow-power on-chip temperature supervisory circuit has also been integrated into the die to safeguard the driver circuit against excessive die temperature (≥220 °C). This approach utilizes increased diode leakage current at higher temperature to monitor the die temperature. The power consumption of the proposed temperature sensor circuit is below 10 μW for operating temperature up to 200 °C.

Testing, characterization, and modeling of SiC diodes for transportation applications

The emergence of silicon carbide- (SiC-) based power semiconductor switches, with their superior features compared with silicon- (Si-) based switches, has resulted in substantial improvement in the performance of power electronics converter systems. These systems with SiC power devices have the qualities of being more compact, lighter and more efficient; thus, they are ideal for high-voltage power electronics applications such as a hybrid electric vehicle (HEV) traction drive. More research is required to show the impact of SiC devices in power conversion systems. In this study, findings of SiC research at Oak Ridge National Laboratory (ORNL), including SiC device design and system modeling studies, are discussed.

Impact of SiC Power Electronic Devices for Hybrid Electric Vehicles

The superior properties of silicon carbide (SiC) power electronic devices compared with silicon (Si) are expected to have a significant impact on next-generation vehicles, especially hybrid electric vehicles (HEVs). The system-level benefits of using SiC devices in HEVs include a large reduction in the size, weight, and cost of the power conditioning and/or thermal systems. However, the expected performance characteristics of the various semiconductor devices and the impact that these devices could have in applications are not well understood. Simulation tools have been developed and are demonstrated for SiC devices in relevant transportation applications. These tools have been verified by experimental analysis of SiC diodes and MOSFETs and can be used to assess the impact of expected performance gains in SiC devices and determine areas of greatest impact in HEV systems. INTRODUCTION Presently, almost all of the power electronics converter systems in automotive applications use silicon(Si-) based power semiconductor switches. The performance of these systems is approaching the theoretical limits of the Si fundamental material properties. The emergence of silicon carbide(SiC-) based power semiconductor switches likely will result in substantial improvements in the performance of power electronics converter systems in transportation applications. SiC is a wide-bandgap semiconductor, and SiC-based power switches can be used in electric traction drives and other automotive electrical subsystems with many benefits compared with Si-based switches. In this paper, experimental characteristics of Si and SiC are used to develop a simulation model for SiC power electronics devices. The main objective of developing these simulation tools is to show some of the systemlevel benefits of using SiC devices in HEVs such as the large reduction in the size, weight, and cost of the power conditioning and/or thermal management systems. Temperature-dependent circuit models for SiC diodes and MOSFETs have been developed. Power losses and device temperatures have been computed for a traction drive in HEVs. Temperature and efficiency profiles have been created for the devices for powering a vehicle over an urban driving cycle. The system benefits in using SiC devices are highlighted through simulation and experimental results. At Oak Ridge National Laboratory (ORNL), a SiC power MOSFET is presently being designed. This power device will be used in power electronics converter systems for automotive applications to demonstrate the benefits of SiC-based power devices. One of the selected automotive applications for this project is a traction drive. New gate drive layouts, circuit topologies, and filter requirements will also be developed to take advantage of the special properties of SiC devices. ADVANTAGES OF SiC COMPARED WITH Si As mentioned earlier, SiC is a wide-bandgap semiconductor, and this property of SiC is expected to yield greatly superior power electronics devices once processing and fabrication issues with this material are solved. Some of the advantages of SiC compared with Si based power devices are as follows: 1. SiC-based power devices have higher breakdown voltages (5 to 30 times higher than those of Si) because of their higher electric breakdown field. 2. SiC devices are thinner, and they have lower onresistances. The substantially higher breakdownvoltage for SiC allows higher concentrations of doping and consequently a lower series resistance. For lowbreakdown voltage devices (~50V), SiC unipolar device on-resistances are around 100 times less; and at higher breakdown voltages (~5000V), they are up __________________________________________________ *Prepared by the Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, managed by UT-Battelle for the U.S. Department of Energy under contract DE-AC05-00OR22725. The submitted manuscript has been authored by a contractor of the U.S. Government under Contract No. DE-AC0500OR22725. Accordingly, the U.S. Government retains a nonexclusive, royalty-free license to publish from the contribution, or allow others to do so, for U.S. Government purposes. to 300 times less [1]. With lower Ron, SiC unipolar power devices have lower conduction losses (Figure 1) and therefore higher overall efficiency. 3. SiC has a higher thermal conductivity and thus a lower junction-to-case thermal resistance, Rth-jc. This means heat is more easily conducted away from the device junction, and thus the device temperature increase is slower. 4. SiC can operate at high temperatures because of its wider bandgap. SiC device operation at up to 600°C is mentioned in the literature [2]. Most Si devices, on the other hand, can operate at a maximum junction temperature of only 150°C. 5. Forward and reverse characteristics of SiC power devices vary only slightly with temperature and time; therefore, SiC devices are more reliable. 6. SiC-based devices have excellent reverse recovery characteristics [3]. With less reverse recovery current, the switching losses and electromagnetic interference (EMI) are reduced and there is less or no need for snubbers. Typical turn-off waveforms of commercial Si and SiC diodes are given in Figure 2. 7. SiC is extremely radiation hard; i.e., radiation does not degrade the electronic properties of SiC. MACHINE AND INVERTER MODELING System level simulation tools have been developed to calculate the conduction and switching losses of the power devices in an inverter used as a motor drive in an HEV. The efficiency of the inverter can then be determined from these losses. The simulation tool is also able to estimate the junction temperature of the power semiconductor devices and recommend an appropriate heatsink size. In this paper, an averaging technique [4] is used to model the power electronics switching losses in an HEV traction drive system. The models are compatible with the Department of Energy’s ADvanced VehIcle SimulatOR (ADVISOR) models. The developed system models use torque and speed values from the ADVISOR simulation to determine the current profile of the system over the Federal Urban Driving Schedule (FUDS). Circuit-level simulation is not practical for this work because the device variables are in microor nanoseconds and the system variables are in 1-second increments. Figure 3 shows the block diagram of the system modeling approach, and Figure 4 shows the three-phase inverter and induction machine for the traction drive system. 300 320 340 360 380 400 420 440 460 480 500 0.01 1

Power-oscillator based high efficiency inductive power-link for transcutaneous power transmission

Transcutaneous power transmission is a critical issue for long term reliable operation of implantable systems. This paper reports a power-oscillator based inductive power link to power up any implantable unit inside the human body. Instead of using power amplifier which requires high drive requirement, two power-oscillator based inductive powering schemes have been presented to achieve high link efficiency. The first scheme utilizes a class-E power oscillator whereas the second scheme uses a differential cross-coupled power oscillator to drive the inductive link. Resonant inductive link has been used to achieve better link efficiency. Simulation results indicate that for a coupling coefficient of 0.45, the class-E power-oscillator based scheme shows a link efficiency of 66% and the differential cross-coupled power-oscillator based scheme shows more than 90% link efficiency. The system has been designed using 0.5-µm standard CMOS process and both of the systems can handle more than 10 mW of power which is adequate for safe operation of biomedical implants.

A low power sensor signal processing circuit for implantable biosensor applications

A low power sensor read-out circuit has been implemented in 0.35 µm CMOS technology that consumes only 400 µW of power and occupies an area of 0.66 mm2. The circuit is capable of converting the current signal from any generic biosensor into an amplitude shift keying (ASK) signal. The on-chip potentiostat biases the chemical sensor electrodes to create the sensor current which is then integrated and buffered to generate a square wave with a frequency proportional to the sensor current level. A programmable frequency divider is incorporated to fix the ASK envelope frequency to be inbetween 20 Hz and 20 kHz, which is within the audible range of human hearing. The entire transmitter block operates with a supply voltage as low as 1.5 V, and it can be easily powered up by an external RF source. Test results emulate the simulation results with good agreement and corroborate the efficacy of the designed system.

An Inductive Link-Based Wireless Power Transfer System for Biomedical Applications

A wireless power transfer system using an inductive link has been demonstrated for implantable sensor applications. The system is composed of two primary blocks: an inductive power transfer unit and a backward data communication unit. The inductive link performs two functions: coupling the required power from a wireless power supply system enabling battery-less, long-term implant operation and providing a backward data transmission path. The backward data communication unit transmits the data to an outside reader using FSK modulation scheme via the inductive link. To demonstrate the operation of the inductive link, a board-level design has been implemented with high link efficiency. Test results from a fabricated sensor system, composed of a hybrid implementation of custom-integrated circuits and board-level discrete components, are presented demonstrating power transmission of 125 mW with a 12.5% power link transmission efficiency. Simultaneous backward data communication involving a digital pulse rate of up to 10 kbps was also observed.

Initial lithography results from the digital electrostatic e-beam array lithography concept

The Digital Electrostatically focused e-beam Array direct-write Lithography (DEAL) concept is currently under development at Oak Ridge National Laboratory (ORNL). This concept incorporates a digitally addressable field-emission array (DAFEA) built into a logic and control integrated circuit to function as the write head for an e-beam lithography tool. The electrostatic focusing is integrated on the DAFEA and consists of additional grids lithographically aligned above the emitters and extraction grid, each separated by a dielectric (nominally low-temperature SiO2) layer. Prototypes of the DAFEA have been fabricated and used to test the focusing of the electron beams and to pattern lines in PMMA resist. First lithography tests have used electron energies of 500 eV to pattern lines less than 1 μm wide at a working distance of 500 μm which extrapolates to <300nm at the nominal DEAL design working distance of 100 μm. Aspects of the DEAL lithography testing and further development are discussed.