Qadeer A. Khan

Bio: Qadeer A. Khan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Buck converter & Settling time. The author has an hindex of 16, co-authored 48 publications receiving 627 citations. Previous affiliations of Qadeer A. Khan include University of Illinois at Urbana–Champaign & Freescale Semiconductor.

High Frequency Buck Converter Design Using Time-Based Control Techniques

Abstract: Time-based control techniques for the design of high switching frequency buck converters are presented. Using time as the processing variable, the proposed controller operates with CMOS-level digital-like signals but without adding any quantization error. A ring oscillator is used as an integrator in place of conventional opamp-RC or G $_{\rm m}$ -C integrators while a delay line is used to perform voltage to time conversion and to sum time signals. A simple flip-flop generates pulse-width modulated signal from the time-based output of the controller. Hence time-based control eliminates the need for wide bandwidth error amplifier, pulse-width modulator (PWM) in analog controllers or high resolution analog-to-digital converter (ADC) and digital PWM in digital controllers. As a result, it can be implemented in small area and with minimal power. Fabricated in a 180 nm CMOS process, the prototype buck converter occupies an active area of 0.24 mm $^{2}$ , of which the controller occupies only 0.0375 mm $^{2}$ . It operates over a wide range of switching frequencies (10–25 MHz) and regulates output to any desired voltage in the range of 0.6 V to 1.5 V with 1.8 V input voltage. With a 500 mA step in the load current, the settling time is less than 3.5 $\mu$ s and the measured reference tracking bandwidth is about 1 MHz. Better than 94% peak efficiency is achieved while consuming a quiescent current of only 2 $\mu$ A/MHz.

A single supply level shifter for multi-voltage systems

Abstract: This paper presents design and application of a level shifter circuit which works with a single power supply. Unlike the conventional level shifter circuits, the proposed level shifter can shift any voltage level signal to a desired higher level without any leakage current. Use of single supply level shifter greatly reduces the supply routing and layout congestion within the chip when level shifting is required between different voltage domains. It also reduces pin count if level shifting is required between two or more chips operating at different supply voltages in a multi-voltage system. The proposed circuit is generic in nature and the voltage range at which level shifting can be done is limited by the technology only. The circuits was designed in 90nm CMOS technology and simulated in SPICE. The simulation results show that the proposed level shifter circuit is able to shift the input signal from 1.2V to 2.5V at maximum frequency of 500MHz.

A 1.2-A Buck-Boost LED Driver With On-Chip Error Averaged SenseFET-Based Current Sensing Technique

Abstract: This paper presents circuit techniques to improve the efficiency of high-current LED drivers. An error-averaged, senseFET-based current sensing technique is used to regulate the LED current accurately. Because the proposed scheme eliminates the series current-regulation element present in all conventional LED drivers, it greatly improves efficiency and reduces cost. The converter operates in three different operating modes, namely buck, buck-boost, and boost modes, and achieves high efficiency over the entire Li-Ion battery range (3-5.5 V). Fabricated in 0.5-μm CMOS process, the prototype occupies an active area of 5 mm2. At 1.2-A LED current, the driver achieves an efficiency improvement of over 13% compared to current-regulation-element-based LED drivers. Measured LED current accuracy is better than 2.8% over the entire range of the battery and its standard deviation measured across seven devices is less than 1.6%. The peak efficiencies are 90.7% and 86% at 600-and 1200-mA currents, respectively.

A self-healing 2.4GHz LNA with on-chip S 11 /S 21 measurement/calibration for in-situ PVT compensation

Abstract: This paper presents a 2.4GHz, reconfigurable RF LNA using on-chip peak detection and calibration to measure and optimize its input impedance (S 11 ) and gain (S 21 ) in-situ, compensating for the unpredictable effects of process, voltage and temperature (PVT) variations. Measurement results show that the calibration of the LNA across PVT corners improves the S 11 by 5.1dB, S 21 by 3dB, while not significantly degrading the Noise Figure (0.22dB degradation) and linearity (1.7dBm degradation).

PVT variation detection and compensation circuit

Abstract: A compensation circuit and a method that compensates for process, voltage and temperature (PVT) variations in an integrated circuit that includes functional modules. The compensation circuit includes a signal generator, a first code generator, a second code generator, and a mapping module. The signal generator generates a first signal and a second signal depending on aligned process corner, voltage and temperature variations and skewed process corner variations respectively. The first code generator receives the first signal, and generates a first calibration code. The second code generator receives the second signal, and generates a second calibration code. The mapping module provides the first and second calibration codes for compensating for the aligned process corner, voltage and temperature variations and the skewed process corner variations associated with the functional modules respectively.

Brain stimulation models, systems, devices, and methods

Abstract: This document discusses, among other things, brain stimulation models, systems, devices, and methods, such as for deep brain stimulation (DBS) or other electrical stimulation. A model computes a volume of influence region for a simulated electrical stimulation using certain stimulation parameters, such as amplitude, pulsewidth, frequency, pulse morphology, electrode contact selection or location, return path electrode selection, pulse polarity, etc. The model uses a non-uniform tissue conductivity. This accurately represents brain tissue, which has highly directionally conductive neuron pathways yielding a non-homogeneous and anisotropic tissue medium. In one example, the non-uniform tissue conductivity is obtained from diffusion tensor imaging (DTI) data. In one example, a second difference of an electric potential distribution is used to define a volume of activation (VOA) or similar volume of influence. In another example, a neuron or axon model is used to calculate the volume of influence without computing the second difference of the electric potential distribution.

A single-inductor 0.35µm CMOS energy-investing piezoelectric harvester

Abstract: Because miniaturized systems store little energy, their lifespans are often short. Fortunately, vibrations are consistent and abundant in many applications, so ambient kinetic energy can be a viable source. Vibrations induce the charges in piezoelectric transducers to build electrostatic forces that damp vibrations and convert kinetic energy into the electrical domain. The shunting switches and switched-inductor circuit of bridge rectifiers in [1-2] increase this output energy by extending the damping (i.e., harvesting) duration within a vibration cycle. Because the output voltages of bridge rectifiers clamp and limit the electrical damping forces built, switched-inductor converters in [3-4], whose damping voltages can exceed their rectified outputs, draw more power from vibrations. Still, electrical-mechanical coupling factors in tiny transducers are low, so electrical damping forces (i.e., voltages) remain weak. Investing energy into the transducer can increase this force, but unlike in [5-6], which demand multiple inductors and high-voltage sources, the system presented here invests energy with only one inductor at low voltages.

Soft start sequencer for starting multiple voltage regulators

Abstract: A soft start sequencer is disclosed for starting a plurality of voltage regulators, the soft start sequencer comprising a first clock for clocking a plurality of soft start circuits, wherein each soft start circuit for ramping a reference signal from a first value to a second value over a ramp time after a delay time. Each soft start circuit comprises a divider operable to divide the first clock by an integer N to generate a second clock, a first counter clocked by the first clock, the first counter operable to time the delay time, and a second counter clocked by the second clock, the second counter operable to time the ramp time after the delay time.

An Overview of the AC-DC and DC-DC Converters for LED Lighting Applications

Abstract: High-Brightness Light Emitting Diodes (HB-LEDs) are considered the future trend in lighting not only due to their high efficiency and high reliability, but also due to their other outstanding chara...

Scalability of Quasi-Hysteretic FSM-Based Digitally Controlled Single-Inductor Dual-String Buck LED Driver to Multiple Strings

Abstract: There has been growing interest in single-inductor multiple-output (SIMO) dc-dc converters due to its reduced cost and smaller form factor in comparison with using multiple single-output converters. An application for such a SIMO-based switching converter is to drive multiple LED strings in a multichannel LED display. This paper proposes a quasi-hysteretic finite-state-machine-based digitally controlled single-inductor dual-output buck switching LED driver operating in discontinuous conduction mode (DCM) and extends it to drive multiple outputs. Based on the time-multiplexing control scheme in DCM, a theoretical upper limit of the total number of outputs in a SIMO buck switching LED driver for various backlight LED current values can be derived analytically. The advantages of the proposed SIMO LED driver include reducing the controller design complexity by eliminating loop compensation, driving more LED strings without limited by the maximum LED current rating, performing digital dimming with no additional switches required, and optimization of local bus voltage to compensate for variability of LED forward voltage VF in each individual LED string with smaller power loss. Loosely binned LEDs with larger VF variation can, therefore, be used for reduced LED costs.