A very compact, rail-to-rail, low-power, high-speed buffer amplifier for LCD driver applications is proposed. A slew-rate enhancement technique based on a dynamic current bias scheme is adopted, and a high slew-rate is obtained without increasing the quiescent current. The buffer amplifier uses a small number of transistors and enables very small active layout area. The proposed buffer amplifier is suitable for both low-and high-voltage LCD driver applications.Introduction: As liquid-crystal displays (LCDs) approach high resolution, high quality, and physically large panel size, the design of output buffer amplifiers becomes more challenging. More specifically, the buffer amplifier needs to be faster in order to deal with larger load capacitance and resistance and thereby achieve smaller settling time. In addition, hundreds or thousands of output buffer amplifiers are integrated into one driver IC, and the buffer should occupy a small die area and consume small static power. It also should provide a rail-to-rail voltage driving capability so that higher grey levels can be accommodated.To reduce settling time, the slew-rate of the buffer amplifier should be increased, because the slewing time normally dominates the settling time in LCD applications. Several techniques have thus far been used to increase slew-rate without additional static power. Lu [1, 2] used additional comparators to sense the rising/falling edges of the input and then turn on push/pull transistors in the output stage to charge/discharge the output load. Yu and Wu [3] proposed a class B buffer in which a comparator is used in the negative feedback path to eliminate the static current in the output stage. Kim and Cho [4] adopted positive feedback loops to speed up the slew-rate of the proposed buffer when there is a voltage difference in the differential input. Choi et al. [5] developed an adaptive dynamic current biasing scheme to increase slew-rate without increasing the quiescent current. In this Letter we propose a very compact low-power high-speed rail-to-rail buffer amplifier using a slew-rate enhancement technique (SRET) based on the adaptive current biasing scheme [5].
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