An Area and Power Efficient Fully Nonlinear 10-bit Column Driver with Time-Shared Multi-Gamma-Slope DAC and Time-Interleaved Sampling Buffer for Mobile AMOLEDs

A color depth of 10 bits or higher is required to provide more natural colors in active-matrix organic light-emitting diode (AMOLED) display panels. The color depth or gamma voltage means the stages or the number of colors that the display can reproduce while it is determined by the bit resolution of the digital-to-analog converter (DAC) in the column driver IC. Fig. 1 (top left) shows a conventional column driver IC including a 10-bit resistor DAC (RDAC) and a buffer amplifier. This architecture suffers from a critical problem in that the number of analog switches is exponentially increased according to the bits, which also makes the RDAC area increase exponentially. Various DACs have been studied to overcome this trade-off between area and bit resolution. One of the promising techniques is the piecewise linear interpolation as shown in Fig. 1 (top right) [1-3, 5-6]. The interpolation column driver includes an upper M-bit RDAC and a lower N-bit interpolation sub DAC, while the sub DAC can adopt a DAC-embedded buffer, a current DAC, or a capacitor DAC, decreasing the area of column drivers. However, these interpolation techniques are still limited due to 'piecewise-linear' output voltages, which cannot cover the whole nonlinear gamma levels for driving the panel. For example, a 10-bit column driver with a 6-bit RDAC and a 4-bit piecewise-linear sub DAC suffers from the lower effective bits (e.g., 7 or 8-bit) for providing nonlinear gamma voltages.