Khondker Zakir Ahmed

A Wide Conversion Ratio, Extended Input 3.5-μA Boost Regulator With 82% Efficiency for Low-Voltage Energy Harvesting

An inductive boost regulator is presented that can harvest energy over a wide input voltage range. The wide input range is enabled by a current-based analog oscillator capable of providing very high duty cycle. The analog control circuits are designed to operate at subthreshold voltage to enable low voltage all electronic autonomous startup. A test chip designed in 130-nm CMOS demonstrates energy harvesting from as low as 12-mV input while biased by an external 1-V battery and autonomous (without using any additional device or battery) startup above 305 mV at output. The design typically consumes 3.5-μA standby current, achieves peak efficiency of 82%, and can regulate output from 0.66 to 3.3 V. The booster is coupled with a thermoelectric generator and the integrated system delivers output power of 6 μW at ~2 °C temperature difference to a maximum of 12 mW at ~50 °C temperature difference.

Characterization of Inverse Temperature Dependence in logic circuits

As the supply voltage (VDD) approaches the device threshold voltage (VT), the elevated temperature results in increased device current. This phenomenon is generally known as Inverse Temperature Dependence (ITD). In this paper, we propose a test structure with a built-in poly-resistor-based heater to characterize ITD in digital circuits. Our measurements from a 130nm test-chip show that the Zero-Temperature-Coefficient (ZTC) point varies by circuit type, and further fluctuates due to process variation. A more accurate ITD-sensitive thermal sensor is thus needed for better temperature tracking.

A 190 nA Bias Current 10 mV Input Multistage Boost Regulator With Intermediate-Node Control to Supply RF Blocks in Self-Powered Wireless Sensors

Self-powered wireless sensors require power delivery systems capable of harvesting from very low input voltage while consuming minimal bias current. This paper presents a multistage boost regulator capable of generating 3 V to supply RF blocks in self-powered wireless sensors from 10 mV input voltage. The bias power consumption is minimized using automated bias gating. The efficiency of the multistage conversion at a high conversion ratio is enhanced through the regulation and control of the intermediate-node voltage. A test chip, fabricated in 130 nm CMOS, demonstrates functional operation from as low as 10 mV input and consumes 190 nA bias current. Single-stage boost regulator demonstrates Peak efficiency of 89%, while the cascaded two stage peaks at 72%. In the cascaded system, the variable intermediate-node voltage operation shows up to 9% efficiency improvement over fixed intermediate-node voltage when operating at high conversion ratio.

Negative Gate Transconductance in Gate/Source Overlapped Heterojunction Tunnel FET and Application to Single Transistor Phase Encoder

Negative gate transconductance (NGT) is shown in gate/source overlapped heterojunction tunnel FET (SO-HTFET). At higher VGS, depletion region in the gate overlapped source region reduces the electric field along channel resulting in reduced band-to-band-tunneling and NGT. Application of SO-HTFET in designing a single transistor binary phase shift-keying with significantly reduced complexity is discussed.

Field programmable thermal emulator (FPTE): An all-silicon test structure for thermal characterization of integrated circuits

This paper presents an on-chip digitally programmable test structure, referred to as the field programmable thermal emulator (FPTE), for on-line characterization of power pattern, time-varying thermal field, and associated changes in the electrical characteristics of the transistors. A test chip was designed in 130nm CMOS to validate the test structure. The measurement results demonstrated the ability of FPTE to emulate various power patterns and capture the effects on temperature and circuit performance.

Post-Silicon Characterization and On-Line Prediction of Transient Thermal Field in Integrated Circuits Using Thermal System Identification

Thermal system identification (TSI) is presented as a methodology to characterize and estimate the transient thermal field of a packaged IC for various workloads considering chip-to-chip variations in electrical and thermal properties. The time-frequency duality is used to identify the thermal system as a low-pass filter in frequency domain through on-line power/thermal measurements on a packaged IC. The identified characteristic system for an individual IC is used for on-line prediction of the transient thermal field of that specific IC for a power pattern. A test-chip, fabricated in 130-nm CMOS, demonstrates the effectiveness of TSI in post-silicon characterization and prediction of transient thermal field. The application TSI in thermal analysis of multicore processors is presented.

A 110nA synchronous boost regulator with autonomous bias gating for energy harvesting

An autonomously bias gated synchronous boost regulator consuming 110nA at 1V is demonstrated in 130nm CMOS. The IC generates regulated 1V output from 30mV input, starts up autonomously (battery-less) at 265mV, and regulates output ranging from 0.78V-3.3V. The peak efficiency is 83% with 10μA and 85% with 10mA load.

Energy efficient active cooling of integrated circuits using autonomous Peltier/Seebeck mode switching of a thermoelectric module

Thermoelectric (TE) devices have shown promise for on-demand cooling of ICs. However, the additional energy required for cooling remains a challenge for the successful deployment of these devices. This paper presents a closed loop control system that dynamically switches a TE module between Peltier and Seebeck modes depending on chip temperature. The autonomous system harvests energy during regular operation and uses the harvested energy to cool during high power operation. The system is demonstrated using a commercial thin-film TE device, an integrated boost regulator and few off chip components. The feasibility of the integration of the TEM and the automated mode switching within the microprocessor package is also evaluated.

An on-chip autonomous thermoelectric energy management system for energy-efficient active cooling

This paper presents an on-chip thermoelectric (TE) energy management system for energy-efficient on-demand active cooling of integrated circuits. Embedding a TE module (TEM) within the package has shown potential for on-demand cooling of integrated circuits (ICs); however, the additional cooling energy limits the effectiveness of TE coolers (TEC). The proposed on-chip system monitors the IC temperature and provides cooling during critical thermal events by operating the TEM in the Peltier mode. During normal operation, the TEM is operated in the Seebeck mode to harvest the otherwise wasted heat energy generated by the IC and reduce the net cooling energy. A boost regulator harvests energy in an output capacitor and a programmable current source controls the cooling. The design is implemented in a 130nm CMOS test-chip, and tested with an external thermoelectric device.

(Invited paper) energy delivery for self-powered IoT devices

Distributed small-scale electronics for IoT applications are on the rise. Power delivery for such electronics requires innovative design techniques to improve energy efficiency. This paper summarizes energy delivery challenges for IoT devices and discusses several design techniques for efficient power delivery units. Such design solutions cover challenges like energy harvesting from very low input voltage, maximized energy harvesting, energy delivery with multiple voltage domains and design using low voltage devices to sustain higher than breakdown voltages.