30 research outputs found
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μ μλΆνμ μ λ ₯ μλͺ¨λ₯Ό μ€μ΄κΈ° μν λ€μν κΈ°λ₯λ€μ ꡬννκ³ μμΌλ©°, μ€μμ²λ¦¬μ₯μΉμ λμ μ μ/μ£Όν μ μ‘°μ κΈ°λ² λ± κ³΅κΈμ μμ λ³νλ₯Ό μλ°νλ κΈ°λ² μμ λ€μνκ² μ μ©λκ³ μλ€. μ΄λ κ° μ₯μΉμ κ³΅κΈ μ μ λ° μ λ₯μ λ³νλ‘ μΈν μ λ ₯ λ³ν νλ‘μ ν¨μ¨μ λ³ν λ₯Ό μ΄λνλ€. λ°λΌμ μ€μμ²λ¦¬μ₯μΉ, λμ€νλ μ΄ λ± μ£Όμ μ λ ₯ μλΉ μ₯μΉμ μ λ ₯ μ κ° κΈ°λ²μ κ°λ°ν λμλ κ°λ³ μ₯μΉμ μ λ ₯ μλΉλ₯Ό μ€μ΄λ κ²κ³Ό λμμ κ°λ³ μ₯ μΉμ λμ ννμ λν μ νν λΆμμ κΈ°λ°νμ¬ λ°°ν°λ¦¬, μ λ ₯ λ³ννλ‘μ μ€κ³κ° ν¨κ»μ΄λ£¨μ΄μ ΈμΌ νλ€. μ ν μ°κ΅¬λ₯Ό ν΅ν΄ λ°°ν°λ¦¬μ νΉμ±μ κ³ λ €ν λ°°ν°λ¦¬ ꡬμ±μ μ΅μ ν κΈ°λ²μ΄ μ μλμλ€ [1].
μ€μμ²λ¦¬μ₯μΉμ λμ μ μ/μ£Όνμ μ μ΄ κΈ°λ²μ μ΄μ΄ μ κΈ°λ°κ΄λ€μ΄μ€λ(OLED) κΈ°λ° λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²μ΄ μ μλμλ€ [2]. μ κΈ°λ°κ΄λ€ μ΄μ€λ λμ€νλ μ΄λ μ λ ₯ μλͺ¨ λ° μμΌκ° λ± κΈ°μ‘΄ μ‘μ νμμ₯μΉμ λΉν΄ μ¬λ¬ μ°μν νΉμ±μΌλ‘ μΈν΄ μ£Όλͺ©λ°κ³ μλ μ°¨μΈλ λμ€νλ μ΄ μ₯μΉμ΄λ€. μ κΈ°λ°κ΄λ€ μ΄μ€λ λμ€νλ μ΄μ μ μ μ λ ₯ μλͺ¨λμλ λΆκ΅¬νκ³ νλ©΄μ λνν λ° ν΄μλμ κ³ λ°λνμ λ°λΌ μμ€ν
μ λ ₯ μλͺ¨μμ μ¬μ ν ν° λΉμ€μ μ°¨μ§νκ³ μλ€. μ κΈ°λ° κ΄λ€μ΄μ€λ λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²(OLED DVS)λ μμμ λ³νμ κΈ°μ΄ν κΈ°μ‘΄μ μ κΈ°λ°κ΄λ€μ΄μ€λ λμ€νλ μ΄ μ λ ₯ μ κ° κΈ°λ²κ³Όλ λ¬λ¦¬ μ΅ μνμ μ΄λ―Έμ§ μ곑λ§μ μλ°νμ¬ λλΆλΆμ μ¬μ§, λμμ λ±μ μ μ©κ°λ₯ν μ λ ₯ μ κ° κΈ°λ²μ΄λ€. ν΄λΉ κΈ°λ²μ κ³΅κΈ μ μμ λ³νμν¬ νμκ° μμΌλ©°, μ΄λ₯Ό μμ€ν
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-μ¨-μΉ© (System-on-a-chip, SoC) κ° μ μλμκ³ , κ·Έ λμ νΉμ±μ΄ λΆμλμλ€. κΈ°μ‘΄ μ€λ§νΈν° λ° νλΈλ¦Ώ PC κ°λ°μ© νλ«νΌμ μ λ ₯ λ³ν ν¨μ¨ λ° λμ νΉμ± μμ λΆμ λμλ€. μ κΈ°λ°κ΄λ€μ΄μ€λ λμ€νλ μ΄μ λμ ꡬλνλ‘ κ³΅κΈ μ μ κΈ°λ²μ λμ νΉμ± λ° μ€λ§νΈν° νλ«νΌμ λμ νΉμ±, λ°°ν°λ¦¬ νΉμ±μ λν λΆμμ κΈ°λ°μΌλ‘ μμ€ ν
μμ€μμμ μ λ ₯ λ³ν ν¨μ¨μ΄ μ΅μ νλμλ€.Modern mobile devices such as smartphone or tablet PC are typically equipped a high-performance CPU, memory, wireless interface, and display. As a result, their power consumption is as high as a small-size laptop computer. The boundary between the mobile devices and laptop computer is becoming unclear from the perspective of the performance and power. However, their battery and related power conversion architecture are only designed according to the legacy design so far. Smartphone and tablet PCs from major vendors such as iPad from Apple or Galaxy-tab from Samsung uses 1-cell Li-ion battery. The laptop PC typically has 3-cell Li-ion battery. The output voltage of the battery affect system-level power conversion efficiency.
Furthermore, traditional power conversion architecture in the mobile computing system is designed only considering the fixed condition where the system-level low-power techniques such as DVFS are becoming mandatory. Such a low-power techniques applied to the major components result in not only load demand fluctuation but also supply voltage changing. It has an effect on the battery lifetime as well as the system-level power delivery efficiency. The efficiency is affected by the operating condition including input voltage, output voltage, and output current. We should consider the operating condition of the major power consumer such as a display to enhance the system-level power delivery efficiency. Therefore, we need to design the system not only from the perspective of the power consumption but also energy storage design. The optimization of battery setup considering battery characteristics was presented in [1].
Beside the DVFS of microprocessor, a power saving technique based on the supply voltage scaling of the OLED driver circuit was recently introduced [2]. An organic light emitting diode (OLED) is a promising display device which has a lot of advantages compared with conventional LCD, but it still consumes significant amount of power consumption due to the size and resolution increasing. The OLED dynamic voltage scaling (OLED DVS) technique is the first OLED display power saving technique that induces only minimal color change to accommodate display of natural images where the existing OLED low-power techniques are based on the color change. The OLED DVS incurs supply voltage change. Therefore we need to consider the system-level power delivery efficiency and battery setup to properly integrate the DVS-enabled OLED display to the system.
In this dissertation, we not only optimize the power consumption of the OLED display but also consider its effect on the whole system power efficiency. We perform the optimization of the battery setup by a systematic method instead of the legacy design rule. At first, we develop an algorithm for the OLED DVS for the still images and a histogram-based online method for the image sequence with a hardware board and a SoC. We characterize the behavior of the OLED DVS. Next, we analyze the characteristics of the smartphone and tablet-PC platforms by using the development platforms. We profile the power consumption of each components in the smartphone and power conversion efficiency of the boost converter which is used in the tablet-PC for the display devices. We optimize not only the power consuming components or the conversion system but also the energy storage system based on the battery model and system-level power delivery efficiency analysis.1 Introduction
1.1 Supply Voltage Scaling for OLED Display
1.2 Power Conversion Efficiency in MobileSystems
1.3 Research Motivation
2 Related Work
2.1 Low-Power Techniques for Display Devices
2.1.1 Light Source Control-Based Approaches
2.1.2 User Behavior-Based Approaches
2.1.3 Low-Power Techniques for Controller and Framebuffer
2.1.4 Pre-ChargingforOLED
2.1.5 ColorRemapping
2.2 Battery discharging efficiency aware low-power techniques
2.2.1 Parallel Connection
2.2.2 Constant-Current Regulator-Based Architecture
2.3 System-level power analysis techniques
3 Preliminary 38
3.1 Organic Light Emitting Diode (OLED) Display
3.1.1 OLED Cell Architecture
3.1.2 OLED Panel Architecture
3.1.3 OLED Driver Circuits
3.2 Effect of VDD scaling on driver circuits
3.2.1 VDD scaling for AM drivers
3.2.2 VDD scaling for PWM drivers
4 Supply Voltage Scaling and Image Compensation of OLED displays
4.1 Image quality and power models of OLED panels
4.2 OLED display characterization
4.3 VDD scaling and image compensation
5 OLED DVS implementation
5.1 Hardware prototype implementation
5.2 OLED DVS System-on-Chip implementation
5.3 Optimization of OLED DVS SoC
5.4 VDD transition overhead
6 Power conversion efficiency and delivery architecture in mobile Systems
6.1 Power conversion efficiency model of switching-Mode DCβDC converters
6.2 Power conversion efficiency model of linear regulator power loss model
6.3 Rate Capacity Effect of Li-ion Batteries
7 Power conversion efficiency-aware battery setup optimization with DVS- enabled OLED display
7.1 System-level power efficiency model
7.2 Power conversion efficiency analysis of smartphone platform
7.3 Power conversion efficiency for OLED power supply
7.4 Li-ion battery model
7.4.1 Battery model parameter extraction
7.5 Battery setup optimization
8 Experiments
8.1 Simulation result for OLED display with AM driver
8.2 Measurement result for OLED display with PWM driver
8.3 Design space exploration of battery setup with OLED displays
9 Conclusion
10 Future WorkDocto
A design for an RGB LED driver with independent PWM control and fast settling time
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (leaves 76-77).A small sized and efficient method to power RGB LEDs for use as backlights in flat panel displays is explored in this thesis. The proposed method is to drive a parallel switched connection of LEDs with a single Average Mode Controlled buck regulator.Specifications for the switching regulator and control circuitry are described. The application circuit demonstrates current settling times between 7[mu]s and 30[mu]s at a switching frequency of 290kHz. Current settling is improved at higher switching frequencies, with settling times approaching a 2[mu]s to 4[mu]s range at 1MHz switching.by Awo Dede O. Ashiabor.M.Eng
The Effects of Spread-Spectrum Techniques in Mitigating Conducted EMI to LED Luminance
Rapid voltage and current changes in recently ubiquitous LED driver have a potency to interfere other devices. Solutions with special converter design, component design, EMI filter, and spread-spectrum techniques have been proposed. Due to cost-size-weight constraints, spread-spectrum technique seems a potential candidate in alleviating EMI problem in LED application. In this paper, the effectiveness of conducted EMI suppression performance of the spread-spectrum technique is evaluated. Spread-spectrum techniques applied by giving disturbance to the system LED driver with 3 profile signals, filtered square, triangular, and sine disturbance signal to the switching pattern of a buck LED driver. From the test results, 472.5 kHz triangular and 525 kHz sine signal can reduce EMI about 42 dBuV whilethe filtered square signal can reduce EMI 40.70 dBuV compare with fundamental constantfrequency reference 669 kHz. The average reduction in the power level of the third signal inthe frequency range of 199 kHz to 925 kHz for 5.154281 dBuV and the filtered square signal can reduce the average power level better than other signal disturbance of 5.852618 dBuV.LED luminance decrease when the spread-spectrum technique is applied to the system about 2814 lux
An Experimental Study of Conducted EMI Mitigation on the LED Driver using Spread Spectrum Technique
LED driver has the potential to interfere the system of electronic devices if the voltage and current change rapidly. Β Several previous studies presented various solutions to overcome this problem such as particular converter design, component design, electromagnetic interference (EMI) filters, and spread-spectrum techniques. Compared to other solutions, the spread-spectrum technique is the most potential way to reduce the EMI in LED applications due to its limited cost-size-weight. In this paper, the effectiveness of conducted EMI suppression performance and the evaluation of its effect on LED luminance using spread-spectrum techniques are investigated. Spread-spectrum is applied to the system by modifying the switching frequency by providing disturbances at pin IADJ. The disorder is given in the form of four signals, namely square, filtered-square, triangular, and sine disturbance signals. The highest level of the EMI suppression of about 31.89% is achieved when the LED driver is given 800 mVpp filtered-square waveform. The highest reduction power level occurs at fundamental frequency reference, when it is given 700 mVpp square disruption signal, is about 81.77% reduction. The LED luminance level will reduce by 85.2% when it is given the four waveforms disruption signals.Β These reductions occur as the switching frequency of the LED driver does not work on a fixed frequency, but it varies in certain bands. LED brightness level has a tendency to generate a constant value of 235 lux when it is given the disruption signals. This disturbance signal causes the dimming function on the system that does not work properly
Self-Configurable Current-Mirror Circuit With Short-Circuit and Open-Circuit Fault Tolerance for Balancing Parallel Light-Emitting Diode (LED) String Currents
published_or_final_versio
Interference Suppression in Massive MIMO VLC Systems
The focus of this dissertation is on the development and evaluation of methods and principles to mitigate interference in multiuser visible light communication (VLC) systems using several transmitters. All components of such a massive multiple-input multiple-output (MIMO) system are considered and transformed into a communication system model, while also paying particular attention to the hardware requirements of different modulation schemes. By analyzing all steps in the communication process, the inter-channel interference between users is identified as the most critical aspect. Several methods of suppressing this kind of interference, i.e. to split the MIMO channel into parallel single channels, are discussed, and a novel active LCD-based interference suppression principle at the receiver side is introduced as main aspect of this work. This technique enables a dynamic adaption of the physical channel: compared to solely software-based or static approaches, the LCD interference suppression filter achieves adaptive channel separation without altering the characteristics of the transmitter lights. This is especially advantageous in dual-use scenarios with illumination requirements. Additionally, external interferers, like natural light or transmitter light sources of neighboring cells in a multicell setting, can also be suppressed without requiring any control over them. Each user's LCD filter is placed in front of the corresponding photodetector and configured in such a way that only light from desired transmitters can reach the detector by setting only the appropriate pixels to transparent, while light from unwanted transmitters remains blocked. The effectiveness of this method is tested and benchmarked against zero-forcing (ZF) precoding in different scenarios and applications by numerical simulations and also verified experimentally in a large MIMO VLC testbed created specifically for this purpose
Automated GPS Mapping of Road Roughness
Many roads across the United States are in poor condition, which can lead to unnecessary accidents and repair costs. In order to alleviate these problems, our group built a second generation road roughness detector that could identify these troubled roads. With the aid of GPS and a mapping program, city officials would now be able to keep track of the condition of their roads. Through examining the first generation design and researching applicable topics, we created a more compact product that was easy to use
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Integrated circuits for efficient power delivery using pulse-width-modulation
Circuits and architectures for efficient power delivery have become crucial in emerging smart systems. Switching power amplifiers (PA) are very attractive for such applications, because they exhibit better efficiency compared to linear PA designs, due to saturated operation. Switching PAs also allow for utilization of deep submicron CMOS technologies, due to which these designs can be easily integrated with digital circuits, and can benefit from process scaling, in performance as well as in area.
Pulse-width-modulation (PWM) is commonly used with switching PAs. A PWM signal typically employs a high-frequency switching pulse waveform as a carrier signal, wherein the pulse-width or duty-cycle of each pulse is modulated by a given low-frequency input signal. The carrier frequency can vary from several kHz to GHz, and is typically determined by the target application.
In this thesis, efficient power-delivery circuits that use PWM with switching class-D stages are presented. Advanced circuit techniques, as well as architectures for PWM are proposed to enhance efficiency and circumvent the limitations of conventional architectures.
A digitally-intensive transmitter using RF-PWM with a class-D PA is described in the first part of the thesis. The use of carrier switching for alleviating the dynamic range limitation that can be observed in classical RF-PWM implementations is introduced. The approach employs the full carrier frequency for half of the amplitude range, and the second harmonic of half of the carrier frequency, for the remainder of the amplitude range. This concept not only allows the transmitter to drive modulated signals with large peak-to-average power ratio (PAPR), but also improves the back-off efficiency due to reduced switching losses in the half carrier-frequency mode. A glitch-free phase selector is proposed that removes the deleterious glitches that can occur at the input data transitions. The phase-selector also prevents D flip-flop setup-and-hold time violations. The transmitter has been implemented in a 130-nm CMOS process. The measured peak output power and power-added-efficiency (PAE) are 25.6 dBm and 34%, respectively. While driving 802.11g 20-MHz 64-QAM OFDM signals, the average measured output power is 18.3 dBm and the PAE is 16%, with an EVM of -25.5 dB.
The second part of the thesis describes a high-speed driver that provides a PWM output using a class-D PA. A PLL-based architecture is employed which eliminates the requirement for a precise ramp or triangular signal generator, and a high-speed comparator, which are typically used for PWM generation. Multi-level signaling is proposed to enhance back-off as well as peak efficiency, which is critical for signals with high PAPR. A differential, folded PWM scheme is introduced to achieve highly linear operation. 3-level operation is achieved without the requirement for additional supply source or sink paths, while 5-level operation is achieved with additional supply source and sink paths, compared to 2-level operation. The PWM driver has been implemented in a 130-nm CMOS process and can operate with a switching frequency of 40-to-170 MHz. For 2/3/5-level PA operation, with a 500 kHz sinusoidal input and 60 MHz switching frequency, the measured THD is -61/-62/-53 dB and corresponding efficiency is 71/83/86% with 175/200/220 mW output power level, respectively. Performance has also been verified for 2/3-level PA operation with a high PAPR signal with 500 kHz bandwidth. While intended as a general purpose amplifier, the approach is well-suited for applications such as power-line communications (PLC).
The final part of the thesis introduces an efficient buck/buck-boost reconfigurable LED driver that supports PWM and PFM operation. The driver is based on peak current control. Rectified sin as well as sinΒ² functions are employed in the reference signal to improve the power factor (PF) and total harmonic distortion (THD) of the buck and buck-boost converters. The design ensures that the peak of the inductor current maintains a constant level that is invariant for different AC line voltages. The operating mode of the design can be changed between PWM and PFM. The LED driver has been implemented in a 130-nm CMOS process. PF and THD are improved when the proposed reference is employed, and peak PF and lowest THD are 0.995/0.983/0.996 and 7.8/6.2/3.5% for the buck (PWM), buck (PFM), buck-boost (PFM) cases, respectively. The corresponding peak efficiency for the three cases is 88/92/91%, respectively.Electrical and Computer Engineerin
Programmable window : a large-scale transparent electronic display using SPD film
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaves 86-87).This research demonstrates that Suspended Particle Device (SPD) film is a viable option for the development of large-scale transparent display systems. The thesis analyzes the SPD film from an architectural display application standpoint, observing its steady-state and dynamic electro-optical response and evaluating different strategies to address, drive and control the independent transparency levels of an SPD pixel array. Although passive matrix multiplexing can also be implemented, it is determined that a directly addressed, multi-line strobing technique is best suited given the constraints of AC drive, power consumption and load bi-directional conductivity of the currently available film. With regards to transparency control, a high-voltage pulse width modulation strategy proves optimal in terms of functionality and component overhead. A prototype display system that incorporates these findings is built, illustrating the key electrical considerations, design features and versatility that ought to be part of future implementations of the system.(cont.) "A huge electronic display on a skyscraper facade can be interesting to passing pedestrians, but if you're inside the building it simply blocks your view. Researchers at MIT's Media Laboratory and Department of Urban Studies and Planning are developing a transparent display that doesn't entirely block incoming light. The group is adapting a commercial available film used in electronic window shades, a high-tech alternative to blinds or curtains that lightens and darkens when electricity is applied and removed. The display will be a matrix of small separate pieces of the film. A grid of tiny wire. will connect the pieces to a computer, which will be able to compose letters and figures in grayscale patters. Because the film at its darkest blocks only 40percent of incoming light, and because only some of the pieces in the matrix. will be darkened at any given time, people sitting behind the display will still be able to see out. "-- Technology Review Magazine, November 2003.by Martin Ramos.M.Eng