Yong-Joon Jeon

A Column Driver with Low-Power Area-Efficient Push-Pull Buffer Amplifiers for Active-Matrix LCDs

Push-pull buffer amplifiers are operated in a transient mode for column drivers suitable for vertical N-dot inversion of an active-matrix LCD (AMLCD) image. Each channel has a static current draw of 3.8 muA and an area of 4773 mum2. The functionality of the column driver with 720 outputs is fully evaluated on the AMLCD module. The chip size of 23.2mm2 is achieved in a 0.35 mum 13.5V CMOS process.

A Piecewise Linear 10 Bit DAC Architecture With Drain Current Modulation for Compact LCD Driver ICs

A piecewise linear 10 bit DAC for LCD data driver with robust interpolation method of drain current modulation is presented. It has higher effective bit resolution than the linear 10 bit switched-capacitor DAC when applied to nonlinear liquid crystal characteristics. By adopting a simultaneous design flow based on the estimations for the mismatch and nonlinearity effects on channel driver performance, the proposed DAC accomplishes good DNL of 0.37 LSB and excellent channel uniformity such that the mean and the standard deviation of the maximum output voltage deviations are 6.35 mV and 0.54 mV, respectively. The data driver with the new interpolation shows 8.2% shrinkage of chip area in comparison with the conventional 8 bit data driver with R-DAC.

A 10b column driver with variable-current-control interpolation for mobile active-matrix LCDs

For high image quality in mobile AMLCDs, the bit depth in a conventional resistor-string DAC (RDAC) needs to be increased, which results in a large area overhead [1]. To avoid this issue, several DAC architectures such as a CDAC [2] and an embedded DAC [3] have been reported. However, CDACs suffer from inaccurate operation and long D/A conversion time due to switching capacitors. An embedded DAC requires a large number of input transistors (=2N+1 for N-bit interpolation) in its amplifier. Moreover, the transistors require large width and length for accurate matching, leading to an area penalty in the amplifier for high bit interpolation (e.g. N≥3). In this paper, an area-efficient and accurate interpolation method that uses variable-current control (VCC) for 10b mobile AMLCD column drivers is presented.

A Direct-Type Fast Feedback Current Driver for Medium-to Large-Size AMOLED Displays

The current or voltage driving schemes are employed for pulse-amplitude modulation (PAM) in AMOLED displays. Current driving methods have advantages over voltage driving schemes including improvement of luminance uniformity at display panels and compensation of TFT characteristics at pixels. degrade the driving accuracy. This paper introduces a direct-type fast feedback current (DFFC) driver that offers fast settling time with good accuracy by comparing the data with the pixel current directly. An optimum compensation method for the feedback loop is suggested as well.

A High-Speed Current-Mode Data Driver With Push-Pull Transient Current Feedforward for Full-HD AMOLED Displays

A push-pull transient current feedforward driver is designed to have a complete push-pull function and loop gain control that enhances the data current drivability. The sink and source current capability of the proposed driver makes it insensitive to the initial voltage levels on the data lines and provides a reduced settling time. The gain control in the positive feedback loop offers a fast settling time without ringing over the complete range of pixel drive currents. The data driver exhibits a settling time of better than 6 μs for drive currents from 20 nA to 5 μA into an equivalent full-HD AMOLED display panel parasitic load of 4 kΩ series resistance and 90 pF shunt capacitance. The driver consumes a static current of 4.5 μA/channel.

Transient Charge Feedforward Driver for High-Speed Current-Mode Data Driving in Active-Matrix OLED Displays

A transient charge feedforward driver (TCFD) is presented for high-speed current-mode data driving in active-matrix organic LED (AMOLED) displays. In order to provide charging current for the parasitic capacitance of a column line (CL), TCFD adaptively generates the required charging current by taking advantage of the parasitic capacitance of another adjacent CL. The TCFD can dramatically enhance the data driving speed by driving a CL with the summing current of data and the required charging current. The adaptive generation of the required charging current and the summing operation are realized by the simultaneous operation of negative- and positive-feedback loops. The loop transfer function is revealed and the stability conditions are discussed. By applying the TCFD, a 7 ¿s driving speed is achieved for 20 nA of data current. The driving speeds are almost constant for CL conditions up to 6 k¿ and 40 pF. The TCFD is fabricated in a standard 0.35-¿m CMOS process and the performance of the TCFD is evaluated by on-chip panel emulation.

56.4: A Cascaded-Dividing Current DAC with Fine Pitch for High-Resolution AMOLED Display Drivers

An 8-bit cascaded-dividing DAC that can operate at a low power supply voltage is proposed. Occupying less than one eleventh of the chip area of a conventional binary-weighted DAC with an equivalent resolution, the proposed DAC features a low operation voltage of 2 V with a good DNL and INL of less than 0.15 LSB. The proposed DAC is expected to be adequate for current-driving AMOLED drivers that have very demanding requirements of a narrow channel pitch as well as high linearity and resolution for the data channel DACs.

P‐40: A Novel Data Driving Method and Circuits for AMOLED Displays

A novel current-mode driving method and driving circuits are proposed for AMOLED displays. The data driving speed in conventional current-mode driving methods is dramatically enhanced by the proposed method and circuits. The proposed method shortens data driving time with feedback of the transient charging current from the parasitic capacitance of an adjacent data line. The current consumption and chip size of the data driver IC are reduced by a half, because one data driving circuit can drive two data lines of a display panel. 10 nA data current can be transferred to the pixel circuit of a display panel with sub-nA accuracy in 15 μsec. The data line parasitic resistance and capacitance are 4 kohm and 20 pF, respectively.

P-45: A Fast Driving Circuit for AMOLED Displays Using Current Feedback

A fast current-mode driving method using current feedback for AMOLED displays is proposed. The proposed driving method dramatically enhanced the driving speed by two negative feedback loops. The loop stability was also guaranteed by the proposed compensation technique and confirmed by simulations. The time to transfer the input current to the pixel current was below 10 usec with sub-nA accuracy for the parasitic loads of 1.5kΩ resistance and 100pF capacitance in data lines.

P-42: A 10 bit Gray Scale Digital-to-Analog Converter with an Interpolating Buffer Amplifier for AMLCD Column Drivers

A 10 bit digital-to-analog converter (DAC) with an interpolating buffer amplifier is proposed for AMLCD column drivers. The proposed circuit is more effective than a conventional circuit in decreasing the DAC (Pass-Transistor Logic) area per channel. The average static current per channel is 1.8 μA and the average interpolating error rate in most of the gray range is a sufficiently small rate of 2.5 % (and less than 0.5 % in the mid-gray range). The uniformity of the channel output is also guaranteed by the proposed error-reduction technique.