A 402-output TFT-LCD driver IC with power control based on the number of colors selected

Abstract

A 402-output thin-film-transistor liquid crystal display (TFT-LCD) driver integrated circuit (IC) with power control based on the number of colors to be displayed is described. To achieve this type of power control, reference voltage buffers are turned on and off according to the selected number of colors. In this architecture, the reference voltage buffers must drive 1-402 capacitive loads, corresponding to a capacitance of 30-12 000 pF. Phase compensation using a zero formed with capacitive loads is proposed for the reference voltage buffers. The introduced zero has a fixed zero frequency for 1-402 loads. An operational amplifier with slew-rate enhancement is also proposed for the buffers. An experimental 402-output TFT-LCD driver IC was fabricated using a 0.6m CMOS technology. The chip size was 2.35 mm 18.1 mm. The quiescent current dissipation of the analog section including decoders was 529 A for 262 144 colors, 182 A for 4096 colors, and 112 A for 512 colors for a 5-V supply.

Low-power high-speed rail-to-rail LCD output buffer with dual-path push–pull operation and quiescent current control

“…For a large-signal step response, the amplifier settling time derives from the combination of a quasi-linear period, depending on the small-signal amplifier performance, and a slew-rate period, related to the amplifier large-signal behaviour. For LCD driver applications, when the output buffer amplifier is required to drive the high capacitive load of the column lines, the amplifier settling time is dominated and restricted by the slew-rate period, as the maximum available current required to charge up the load capacitor is limited in low-power conditions [14].…”

“…Moreover, as a high open-loop gain is required to obtain a low-valued systematic offset voltage, a two-stage amplifier architecture is traditionally adopted in the LCD driver [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Since the additional Miller capacitance required for frequency compensation would involve a sensible silicon area consumption, most recently proposed amplifiers achieve stability by exploiting dominant-pole compensation at the high-capacitive-impedance output node.…”

“…However, to provide fast driving capabilities to the output stage, a few additional current comparators are commonly included in the basic two-stage amplifier topology, in order to improve large-signal performance by sensing the rising and falling edges of the input waveform and switch on additional driving transistors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Nevertheless, although the current comparators allow to enhance the output amplifier slew-rate, a current mismatch is required to turn off the output devices during quiescent operation.…”

Low Offset and High Slew Rate Buffer amplifier for LCD Application

“…The author proposed this charge-recycling method to reduce the power consumption incurred in driving highly capacitive column lines by storing the charge into the external capacitors and reusing it in the next cycle. Itakura et al [13][14][15][16][17][18][19][20] proposed an output amplifier in which the phase compensation is achieved by introducing a zero, which is formed by the load capacitance and the phase compensation resistor connected between the output of the amplifier and the capacitive load.…”

A High Slew Rate Buffer Amplifier Employing MTCMOS Technique for Flat Panel Display

“…There are so many design challenges for the output buffer of an of an LCD (Liquid crystal display) driver [6]. The number of outputs to be achieved by using several column drivers of the buffer amplifier, so it should be used to minimize the system costs and increase the reliability of the circuit [7][8]. A flat panel display column driver three special requirements for the output buffer are to be needed.…”