Seok-Jeong Song

Bilinear weighting and threshold scheme for low-power two-dimensional local dimming liquid crystal displays without block artifacts

Abstract. A two-dimensional (2-D) weighted roll-off local dimming algorithm that eliminates any visible block artifacts caused by the spatial mismatch between a discontinuous panel image and a continuous backlight is described. The proposed scheme enhances the high gray details by means of a roll-off scheme and removes the block artifacts with bilinear weighting of a pixel-compensated panel image. In addition, the threshold scheme is used to resolve overcompensation problems that lead to visible artifacts around the boundaries of dark local blocks. The image quality and the power consumption are evaluated for 40 test images through both simulation and measurement. Compared to 15.56 and 1.45 of a 2-D roll-off method, the maximum and average color difference values of a proposed scheme are reduced to 7.76 and 0.72 in the simulation. For a prototype 40-in. light emitting diode TV, the average power saving over 40 test images is measured as 60.96%.

In-Pixel Mobility Compensation Scheme for AMOLED Pixel Circuits

This paper demonstrates an in-pixel mobility compensation scheme for AMOLED pixel circuits, which requires only one capacitor and one TFT additionally. The proposed scheme converts the mobility variation into the voltage that is subtracted from the gate voltage of a driving TFT to reduce the current error. The proposed structure is applicable to both n-type and p-type TFT pixel circuits and is robust to the process variation of capacitors because the ratio of two capacitors is utilized. SPICE simulations show that, on average, the current error reduction of 50.1%, 34.9%, and 63.3% is achieved for n-type LTPS TFT, p-type LTPS TFT, and n-type oxide TFT pixel circuits, respectively, compared with a normal pixel circuit without mobility compensation.

Sound-of-Tapping user interface technology with medium identification

Abstract Touch screen technologies have become the mainstream of input interfaces for mobile devices. However, due to the small size screens, it is difficult to offer more than two inputs at the same time. In order to achieve input richness, this paper proposes a new sound-of-tapping (S-TAP) technology that is a novel user interface utilizing only microphones embedded in most mobile devices. S-TAP technology extracts the positions of tapping sounds generated at the outside of a smartphone by means of frequency domain features and support vector machine (SVM). The error ratio of an S-TAP algorithm implemented in a smartphone is measured as 8.6%. Additionally, this technology enables the smartphone to identify mediums that the user is tapping on. In the end, we demonstrate two smartphone applications to scroll web pages only by S-TAP and to zoom and rotate a map image by S-TAP as well as touch screen.

Visible Light Identification System for Smart Door Lock Application with Small Area Outdoor Interface

Visible light identification (VLID) is a user identification system for a door lock application using smartphone that adopts visible light communication (VLC) technology with the objective of high security, small form factor, and cost effectiveness. The user is verified by the identification application program of a smartphone via fingerprint recognition or password entry. If the authentication succeeds, the corresponding encoded visible light signals are transmitted by a light emitting diode (LED) camera flash. Then, only a small size and low cost photodiode as an outdoor interface converts the light signal to the digital data along with a comparator, and runs the authentication process, and releases the lock. VLID can utilize powerful state-of-the-art hardware and software of smartphones. Furthermore, the door lock system is allowed to be easily upgraded with advanced technologies without its modification and replacement. It can be upgraded by just update the software of smartphone application or replacing the smartphone with the latest one. Additionally, wireless connection between a smartphone and a smart home hub is established automatically via Bluetooth for updating the password and controlling the home devices. In this paper, we demonstrate a prototype VLID door lock system that is built up with LEGO blocks, a photodiode, a comparator circuit, Bluetooth module, and FPGA board.

Electrochromic display driving scheme for high dynamic range image capture

This paper describes a new high dynamic range (HDR) image capture system that utilizes an electrochromic display (ECD). The ECD panel reduces the transmittance of bright area and increases the transmittance of dark area, which retain as much information as possible without saturation at high or low luminance. A passive matrix driving scheme is employed for the ECD due to low cost and high transmittance and the column and row driving voltages are obtained by least square error method. The resulting information gain defined as the maximum gray scale ratio of HDR and normal images is 1.73.

Hybrid Voltage and Current Programming Pixel Circuit for High Brightness Simultaneous Emission AMOLED Display

This paper describes a new simultaneous emission AMOLED pixel circuit to achieve high brightness. Unlike the previous simultaneous emission scheme, the proposed one allows the programming operation to take place at the same time with the emission of OLEDs, which leads to high brightness. The proposed hybrid pixel circuit consists of programming and driving parts. The programming part compensates for the threshold voltage variation by means of a voltage programming scheme and the driving part is updated from the programming part through the internal current programming scheme. The SPICE simulation ensures that the proposed scheme dramatically reduces the average current error to 1.5% and 4.0% as to the threshold voltage variations of ±0.2 V and ±0.5 V, respectively. In addition, because approximately the whole frame time can be secured for the emission period, the output luminance loss is alleviated substantially compared with the previous method.