Sang-Hui Park

A highly noise-immune touch controller using Filtered-Delta-Integration and a charge-interpolation technique for 10.1-inch capacitive touch-screen panels

Capacitive touch-screen panels (TSPs) are widely used in recent high-end mobile products on the basis of their high quality of touch features, as well as superior visibility and durability [1-5]. Capacitive TSPs can be classified into self-capacitance [1,2] or mutual-capacitance [3-5] types, according to the sensing mechanism. Compared with the self-capacitance types, which offer low cost and high scan frequency from the simple line-sensing scheme, the mutual-capacitance types, which read out all sensor pixels, are presently widely preferred due to their multi-touch capabilities. However, the reduced sensing time for each sensor makes it difficult to achieve a high signal-to-noise ratio (SNR). Therefore, good noise performance in the analog front-end of the touch controller is essential for mutual-capacitance type TSPs.

12.5 An error-based controlled single-inductor 10-output DC-DC buck converter with high efficiency at light load using adaptive pulse modulation

Reducing the number of large external components, especially inductors, is a very important issue for Power-Management ICs (PMICs). Single-Inductor Multiple-Output (SIMO) converters are excellent candidates to meet this requirement [1-3]. However, there are several issues with SIMO converters, such as cross regulation, instability and inefficiency at light load. Under normal load conditions, comparator-based controlled SIMO converters [1,2] show good cross regulation performance due to the fast response of the comparator. However, the switching loss remains constant and degrades light load efficiency due to the fixed switching frequency of output switches. The low-efficiency characteristic when any output is under light load condition is a critical issue that must be solved because a SIMO converter is very suitable for light load applications. In addition, the cross regulation issue appears again when any output is under no load because the output receives energy from the inductor every cycle despite the load condition. To solve these issues, a SIMO converter was previously reported to support Pulse Frequency Modulation (PFM) mode [3]. However, the mode change control method increases the complexity of the control loop, which makes it unsuitable for a multi-output SIMO converter. In this paper, an Error Based Controlled (EBC) SIMO converter is presented to resolve the problems raised above using load-dependent Adaptive Pulse Modulation (APM). A hybrid topology composed of a switching converter and a linear regulator is also presented to minimize the cross regulation issue. To highlight the advantages, a 10-output SIMO converter is designed.

6.8 A pen-pressure-sensitive capacitive touch system using electrically coupled resonance pen

Capacitive touch systems for finger touch have become widely used in mobile devices such as smartphones, tablets, and so on. Beyond ordinary touch functions, some devices adopt an extra electromagnetic resonance (EMR) system [1] to support pens for advanced user experiences; these devices have been successfully commercialized for high-end devices [2]. Such devices offer a realistic and accurate pen-based drawing experience for consumers using a battreryless, light, and pressure-sensitive pen; this is possible because the EMR system excites a passive pen via magnetic coupling and senses the pens returning signal that contains coordinate and fine pen-pressure information. As shown in Fig. 6.8.1 (top), an EMR system, however, requires an additional costly sensor board made with a flexible printed circuit board beneath a display panel to find coordinates of the EMR pen via a magnetic field and a dedicated controller, and it also consumes excessive power. If a capacitive touch system could cover the function of the EMR system, it would be a cost-effective and compact solution in terms of re-utilizing an existing system without the additional sensor board and EMR controller. In this paper, a capacitive touch system sensing a passive pen with pen pressure as well as a finger is introduced as an alternative to an EMR system.

A 5.6mV inter-channel DVO 10b column-driver IC with mismatch-free switched-capacitor interpolation for mobile active-matrix LCDs

To achieve high image quality in mobile active-matrix LCDs, higher DAC resolution and good channel-to-channel uniformity are required in column-driver ICs. In conventional column-driver ICs, the resistor-DAC (R-DAC) architecture has been generally used due to its uniform characteristic, because each R-DAC in driver channels shares a common resistor string for gamma reference-voltage generation. Furthermore, nonlinear gamma correction can be easily implemented using a nonlinear resistor-string that has an inverse transfer curve to the liquid crystal (LC) response. However, the increase in color depth for LCDs results in a large chip-size overhead, thus disclosing the limitation of the R-DAC architecture. To overcome this issue, several hybrid DAC architectures composed of a main 6b R-DAC and a 4b sub-DAC with various interpolation schemes have been reported [1-5]. Their linear interpolation schemes reduce the driver channel size. Meanwhile, their linear 4b interpolation leads to the loss of effective bit resolution for nonlinear gamma correction. In addition, the inevitable mismatch between respective sub-DACs has a significant influence on the channel-to-channel uniform performance of a column-driver IC. In this paper, we present a 10b column-driver IC with a mismatch-free switched-capacitor (SC) interpolation scheme for mobile AMLCDs. The proposed mismatch-free interpolation scheme provides further reduction of the driver size, good linearity, highly uniform channel performance, and more effective bit resolution.

High Area-Efficient DC-DC Converter With High Reliability Using Time-Mode Miller Compensation (TMMC)

This paper presents a novel on-chip compensation scheme, the Time-Mode Miller Compensation (TMMC), for DC-DC converter in which the compensation components are integrated on-chip. Using this proposed scheme, the DC-DC converter is stably compensated and insensitive to process variations, with significantly small compensation components ( 1 pF and 80 kΩ in this work) consuming very small silicon area owing to the characteristic of the TMMC. The small compensation components make the chip size small, with 0.12 mm2 of core area (w/o power transistors) using 0.18 μm I/O process. This core size is as small as that of the digital DC-DC converters implemented with less than sub-50 nm process. The measurement result shows that the maximum power efficiency of 90.6% is obtained at the load current of 220 mA with the switching frequency of 1.15 MHz when the input and the output voltages are 3.3 V and 2 V, respectively.

An Error-Based Controlled Single-Inductor 10-Output DC-DC Buck Converter With High Efficiency Under Light Load Using Adaptive Pulse Modulation

An error-based control method is proposed for a single-inductor multiple-output (SIMO) converter that maintains high efficiency under various load conditions. A peak efficiency of 88.7% was achieved with one output (IO1) of 5 mA, while the other outputs are at 432 mA. A hybrid topology composed of a switching converter and a linear regulator is also presented for fast load transient response. The proposed SIMO buck converter was fabricated with a 1P4M 0.35 μm BCD process and has 10 independently regulated outputs. The measured load transient waveform shows cross regulation of 0.1 mV/mA and a load transient of 0.17 mV/mA. This was achieved under load transient conditions for one output (IO9) in between 1 mA and 100 mA with the other outputs at 422 mA.

Inverting Buck-Boost DC-DC Converter for Mobile AMOLED Display Using Real-Time Self-Tuned Minimum Power-Loss Tracking (MPLT) Scheme With Lossless Soft-Switching for Discontinuous Conduction Mode

A DC-DC converter, which tracks minimum power loss under various conditions, is presented in this paper. With this DC-DC converter, a new approach for optimum efficiency, which implements theoretical equations intactly at the circuit level, was adopted. This approach has high reliability against process variation. The concept of lossless soft-switching was also adopted in discontinuous-conduction-mode (DCM) operation. The proposed DC-DC converter has a maximum power efficiency of 91% at the switching frequency of 1 MHz. The proposed converter is able to maintain a maximum power efficiency of around 90% over the whole range of input voltage from 2.9 to 4.5 V and output voltage from -3.8 to -5.9 V. This chip is implemented in a 0.35 μm BCD process and occupies an area of 2.1 ×1.4 mm2.

10.4 A hybrid inductor-based flying-capacitor-assisted step-up/step-down DC-DC converter with 96.56% efficiency

The number of mobile device users increases every year. Each mobile device is usually equipped with a Li-ion battery having voltage that varies from a minimum of 2.7V to a maximum of 4.2V. Therefore, as the battery voltage decreases with time, a DC-DC converter is required for a regulated supply lower or higher than the battery voltage. A simple buck converter is not suited for this case, since step-up conversion is not available [1]. Instead, a non-inverting buck-boost converter can be a solution over the entire range of the battery voltage [1–4]. Many research studies related to buck-boost converters operated on Li-ion batteries set the target output voltage at around 3.4V [3,4]. Since Li-ion batteries have a wide plateau from 3.6V to 3.8V and a small energy storage below the plateau, DC-DC converters are generally operated on step-down mode at most of the battery voltage range, as shown in Fig. 10.4.1 top. Notwithstanding, step-up conversion is also required for extracting the energy below the plateau even if it is a small amount in the battery. Therefore, in DC-DC converters, it is critical to maintain high efficiency over the whole range of the battery voltage when it operates on both step-down and step-up modes to prolong the battery usage effectively. However, if the conventional buck-boost topology of Fig. 10.4.1 bottom-left is used for step-up and step-down purposes, there are always two switches (S1 and S3) conducting in the main current path through the inductor. Thus, the switches become large in size to minimize the conduction loss. As the switching loss also increases when the switch size is larger, the efficiency of this structure is usually lower than that of the simple buck (or boost) converter [1]. In this respect, this paper proposes a topology named a flying-capacitor buck-boost (FCBB) converter suitable for such an application by obtaining both step-up and step-down operations with high efficiency throughout the whole range of the battery voltage.

A Pen-Pressure-Sensitive Capacitive Touch System Using Electrically Coupled Resonance Pen

A touch system sensing pen-pressure of the proposed electrically coupled resonance (ECR) pen is implemented, which can replace costly digitizer system containing electro magnetic resonance (EMR) and capacitive touch system. The proposed system detects the location of the ECR pen and finger using proposed position sensor, and senses pen-pressure of ECR pen using proposed pen-pressure sensor. For the position sensor, to detect even small variation of the mutual capacitance on touch screen panel (TSP) of the pen, a simultaneous driving scheme is proposed with modified Hadamard matrix, resulting in highly increased dynamic range and SNR. In the proposed pen-pressure sensor, the resonant frequency of the ECR pen is measured by a frequency to voltage converter based sensor. The measured SNR for the pen position is 49 dB with 1 mm φ metal pillar, and 6.5-bit resolution is achieved for pen-pressure sensor in 6σ criteria.

Hybrid driver IC for real-time TFT non-uniformity compensation of ultra high-definition AMOLED display

An UHD AMOLED display driver IC, enabling real-time TFT non-uniformity compensation, is presented with a hybrid driving scheme. The proposed hybrid driving scheme drives a mobile UHD (3840×1920) AMOLED panel, whose scan time is 7.7μs at a scan frequency of 60Hz, through the load of 30kohm resistance and 30pF capacitance. A proposed accurate current sensor embedded in the column driver and a back-end compensation scheme reduce maximum current error between emulated TFTs within 0.94 LSB (37nA) of 8-bit gray scales. Since the TFT variation is externally compensated, a simple 3T1C pixel circuit is employed in each pixel.