tailieunhanh - composite 2012 Part 10

Tham khảo tài liệu 'composite 2012 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TFT-LCD Driver IC Design 173 depth displays. As an alternative previous research has proposed an LCD column driver using a linear switched capacitor DAC 2-3 . In this case the timing controller compensates for the nonlinear LC characteristic which greatly reduces the die area. To reduce the die area the current study proposes a 10-bit LCD column driver the use of an R-DAC and a charge sharing DAC C-DAC for each channel. This approach applies gamma voltages to the R-DAC to fit the inverse of the liquid crystal characteristic. The gamma correction can also be digitally fine-tuned in the timing controller or column drivers. 2. Conventional column drivers Figure 3 shows the conventional column driver architecture 1 8 . The column driver supplies high analog voltages to the LCD panel. To reduce power consumption the digital circuit uses a low voltage power supply. Digital display data is fed to the RGB inputs and sampled into the input registers. A wide data latch presents one row of serial input pixel data to the level shifters inputs. The level shifters then boost the digital signals to higher levels. The DAC of each channel outputs a voltage level corresponding to a digital sub-pixel code. The output buffers drive the highly capacitive data lines of the LCD panel 11-12 . For a dot inversion operation the DACs offer voltages with positive and negative polarities for the same digital input code. Hence 11-bit DACs are needed for a 10-bit column driver. Fig. 3. The conventional column driver architecture. Since the transmittance response of the liquid crystal to the applied voltage is nonlinear a nonlinear DAC is needed to obtain a linear transmittance with the digital code. Applying certain gamma voltages to the resistor string of the nonlinear DAC and the resistor string is made up of unequal resistors to fit the nonlinear curve. Figure 4 depicts the layout of a conventional column driver. One resistor string is put in the middle of the chip to supply the reference .