Slew-rate-enhanced rail-to-rail buffer amplifier for TFT LCD data drivers

Abstract

A high-slew-rate low-power rail-to-rail buffer amplifier, which is suitable for thin film transistor liquid crystal display (TFT LCD) data driver applications, is proposed. Previous dynamic biasing approaches become ineffective as an output signal approaches VDD or VSS supplies. However, the proposed buffer amplifier with a dynamic biasing circuit enhances the slew rate throughout the entire rail-to-rail signal range. The buffer amplifier and the previous counterparts were fabricated in a 0.35 mm CMOS technology with 3.3 V supply voltage. Measurements show that the slew rate for rail-to-rail signal transition is enhanced from 0.80 V/ms of a previous counterpart to 2.75 V/ms. Introduction: Higher resolution and frame frequency are required on thin film transistor liquid crystal displays (TFT LCDs) for natural motion picture and three-dimensional displays. The frame frequency should be elevated from typically 60 to 480 Hz [1]. Consequently, the driving time for each row must be decreased inverse proportionally, and TFT LCD data drivers should be equipped with high-slew-rate buffer amplifiers to accommodate the need for decreased driving time.In addition, data drivers should have the rail-to-rail input range to cover the liquid crystal driving voltage and also have the push-pull output stage to support N-dot polarity inversion driving for high image quality and low power consumption [2]. The rail-to-rail foldedcascode class-AB amplifier in [3] is widely used to meet these requirements.Several buffer amplifiers for TFT LCD data drivers have been proposed to enhance the slew rate with minimal increase in the quiescent current [4][5][6][7]. In [4], the buffer amplifier uses comparators to sense the slewing conditions, but it does not support the push-pull operation. In [5], an additional current path is inserted, but the circuit requires a clock signal, which increases the circuit complexity and power consumption. The dynamic biasing circuits in [6] and [7] detect the slewing conditions and turn on the auxiliary current sources. The enhancement of the slew rate, however, ceases when the output voltage approaches VDD or VSS, which degrades the overall slew rate for the rail-to-rail signal swings. In this Letter, we propose a buffer amplifier for a TFT LCD data driver with a dynamic current biasing circuit that enhances the slew rate in the entire rail-to-rail signal range.

An 11‐μ W, 9‐bit fully differential, cyclic/algorithmic ADC in 0.13 μm CMOS

“…Amplifiers with improved SR are presented in –. These amplifiers employ positive feedback that detects when slewing occurs and delivers uncontrolled large current to the main amplifier.…”

High-Speed Column Driver IC Having Buffer Amplifier with Embedded Isolation Switch and Compact Adaptive Biasing for Flat-Panel Displays

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