Display Electronics Group

◈ Display Driver IC (DDI) 

    ◇ Introduction


- An active matrix liquid crystal display (AMLCD) is a type of flat panel display, currently the overwhelming choice of laptop
computer manufactures, due to low weight, very good quality, wide color gamut and response time. However, AMLCD
power-consumption is high due to 
two critical factors; AC power of charging and discharging for the data line in display panel,
DC power of quiescent current for OP-AMP operation. Therefore, it is important to reduce power consumption of AMLCD.

- Low temperature polycrystalline silicon thin film transistors (LTPS TFTs) have been used for the backplane of the active
matrix displays (AMDs). In spite of the superior device performance compared to the other backplane like amorphous silicon
(a-Si:H) TFTs, LTPS TFTs have disadvantages.

Display driver IC (DDI) team in IELAB strives for the researches about driving methods for AMLCD. Our group have proposed
driving methods to reduce power consumption in AMLCD; charge sharing method, stepwise driving method. Moreover, our
group have proposed a shared column-line driving method to reduce manufacturing cost. And, our group also strives for the
researches about gate driver in LTPS-TFT LCD. Our group have performed the gate driver, the DC-DC converter and the level

    ◇ Research area
      · Development of driving circuits using LTPS TFTs for LTPS-LCD

High-speed signaling system

    ◇ Research results
      · Triple charge sharing method

Block diagram of the data driver using the
proposed triple charge sharing method

Output waveforms and timing diagram of the
proposed data driver

    ◇ Research results
      · Stepwise driving method

Stepwise capacitance driving circuit

Measured waveforms of stepwise
data drivers with control signals

Measured power saving efficiency
with load conditions

    ◇ Research results
      · Shared column-line driving (SCLD) method

The pixel structure of the proposed
shared column line driving method

The waveform of the scan pulse and
driving sequence of the proposed SCLD

The block diagram of the new data driver
for the proposed SCLD method

    ◇ Research results
      · The block diagram of the new data driver for the proposed SCLD method

Panel demonstration using 42-inch panel

    ◇ Research results

· P-type only gate driver · P-type only gate DC-DC converter

Schematic of p-type only gate driver

Schematic of P-type only DC-DC converter

Layout of p-type only gate driver of single stage

Layout of p-type only
DC-DC converter

Measured output waveforms of p-type only gate driver

Measured output waveforms of p-type only DC-DC converter

    ◇ Research results
      · CMOS level shifter

Schematic of CMOS level shifter

Measured output waveforms of CMOS level shifter

Layout of CMOS level shifter

◈ AMOLED display 

    ◇ Introduction


- AMOLED display technology is most powerful candidate for the next generation displays. It has many advantages such as
light weight, thin form factor, wide viewing angle, vivid color, fast response, and so on. Furthermore, AMOLED displays
are proper to realize flexible and transparent displays, thus it is a hot research field.

- In order to realize AMOLED displays, OLED Group of IELAB has researched a number of driving methods, pixel structures,
peripheral driving circuits and driving algorithms for high quality AMOLED displays since 2002. The 18 journal papers and 34
conference papers have been published. The OLED group is interested in high resolution AMOLED display, large-sized
AMOLED TV, feedback system for luminance non-uniformity compensation, etc.

    ◇ Panel Demonstration

Current programmed boost type structure.

Voltage programmed boost type pixel

2.1-inch QCIF(176×220) full color

5-inch WVGA(800×480) full color
AMOLED panel

14-inch 1366×768 AMOLED display

    ◇ Research results

3.5-inch 480×800 luminance compensation using camera

    ◇ Research results
      · 8-bit Current Source Driver IC for Small-Size AMOLED Displays

Source Driver IC

2.1-inch qVGA AMOLED

    ◇ Research results
      · 10-bit Current Source Driver IC for Large-Size AMOLED Displays

Full chip size : 16,800 mm x 3,600 mm

◈ Micro Display

    ◇ Introduction


- Recently, microdisplays can be useful for various display applications such as pico-projectors for handheld electronics, digital
movie-projectors, and head-mounted-displays (HMDs). The technologies for microdisplays are classified as digital light
projectors (DLP), liquid-crystal-on-silicon (LCoS), and organic light-emitting diode-on-silicon (OLEDoS). One among these
technologies, an OLEDoS has many advantages such as lightweight, thinness, and low power consumption.

- Micro Display team in IELAB strives for the researches about microdisplay using various technology. The design of the pixel
structure, data driver and gate driver.

    ◇ Research areas
      · The pixel circuit, data driver and gate driver
      · Microdisplays for various application
           - Pico-projector
           - Head Mounted Display

           - Spatial optical modulator (SOM)

Optical modulation scheme

Single-pixel ribbon structure

Conceptual diagram of a projection display system using a SOM device

           - OLED on silicon (OLEDoS)
           - Single crystalline Si wafer + CMOS process + white OLED + color filter

    ◇ Research results
      · OLED-on-Silicon (OLEDoS)
          - Process: 0.35-mm CMOS
          - Area: 0.6-inch
          - Resolution : XGA (1024 X 768)
          - Color depth : 8-bit

0.6-inch 8bit XGA OLEDoS layout

0.6-inch 8bit XGA OLEDoS demonstrate image

◈ Nanowire transistor and transparent display

    ◇ Introduction


- Recently, the transparent and flexible displays are gradually requiring due to wide application field and convenience for
carrying, the transparent and flexible display can be realized by nanowire transistor and oxide TFT.

- Nanowire transistor and transparent display team in IELAB strives for the researches about flexible and transparent display.
1) Analyzing the NSEA electrical characteristics and researches of the pixel structure to compensate the TFT electrical
characteristic variation.
2) Oxide TFT modeling and researches of the shift register

    ◇ Research results

      · Nanowire transistor
          - SnO2 nanowire(W/L : 60nm / 10nm)
          - Channel region : W/L = 14μm/3μm
          - Gate(ITO) – 100nm
          - Gate insulator(Al₂O₃) – 30nm
          - Source/Drain metal – Al(50 nm)+ITO(70 nm)

Cross view & FE-SEM image

VDS-IDS & VGS-IDS characteristics

    ◇ Research results

      · Shift register using nanowire transistor
          - Multi-stage shift register using parallel connection technique of n-channel nanowire transistors for low output noise
          - 5 V of input voltage, 900 Hz of operating frequency

Micrograph of shift register and FE-SEM of nanowire transistor

Measured results

    ◇ Research results

      · Measurement of oxide TFT characteristics
          - Width / length = 40 / 7 (μm / μm)

Measured TFTs

Uniformity of transfer characteristics

◈ LED backlight dimming technology

    ◇ Introduction


- Liquid crystal displays (LCDs) are used in a wide range of consumer products because of light weight, high resolution, good
color performance and other advantages. However, there are two major drawbacks which are low image contrast ratio and
large power consumption. In conventional LCDs, the image is displayed by controlling the LC transparency with constant
backlight luminance. The image contrast ratio is poor because the light is not blocked completely at the lowest gray level.
The power consumption is appreciably large because the backlight always operates with the full luminance regardless of input
image. To solve these problems, backlight dimming algorithms have been studied by many researchers. The backlight dimming
algorithm is defined as the dynamic control of backlight luminance according to input image.

    ◇ Trend

Trend in cutting FPD TV power consumption

Backlight accounts for two-thirds of total LCD TV power consumption

Input image

Dimmed backlight

Backlight dimming algorithm

Process of backlight dimming algorithm

55inch LCD panel with RGB LED backlight