CAPACITIVE LOAD DRIVE CIRCUIT AND DISPLAY DEVICE INCLUDING THE SAME

• US 20110074755A1
• Filed: 06/02/2009
• Published: 03/31/2011
• Est. Priority Date: 08/11/2008
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ogawa, Yasuyuki, Brown, Christopher
• Granted Patent: US 8,487,922 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A buffer circuit drives a capacitive load based on a voltage Vin. In a setup period, switches are in an ON state, and in a drive period, a switch is in an ON state. A voltage comparison unit compares the voltage Vin in the setup period and a voltage Vout in a drive period to output a comparison result voltage. A push-pull output unit includes a TFT for charge and a TFT for discharge. A drive control unit controls the TFTs to be in an OFF state in the setup period, and in the drive period, selectively controls the TFTs to be in an ON state in accordance with the comparison result voltage. If Vout<Vin, the comparison result voltage rises, the TFT becomes in an ON state, a voltage at a node falls, the TFT becomes in the ON state, and the voltage Vout rises. Thus, there is a provided a small-sized capacitive load drive circuit with low power consumption and robust against process variation.

Claims

1. A capacitive load drive circuit that drives a capacitive load based on an input voltage, comprising:

a voltage comparison unit that compares the input voltage inputted from an input terminal and an output voltage outputted from an output terminal to output a comparison result voltage in accordance with a comparison result;

a drive control unit that outputs a charge control voltage and a discharge control voltage that are set to initial levels respectively in a first period, and change in accordance with the comparison result voltage in a second period; and

a push-pull output unit including a charge circuit that charges the capacitive load connected to the output terminal, based on the charge control voltage, and a discharge circuit that discharges the capacitive load, based on the discharge control voltage, wherein

the drive control unit selectively operates the charge circuit and the discharge circuit so that the output voltage becomes equal to the input voltage.

2. The capacitive load drive circuit according to claim 1, wherein the voltage comparison unit includes:

an input-side selection switch that is provided between the input terminal and a predetermined node, and becomes in an ON state in the first period;

an output-side selection switch that is provided between the output terminal and the node, and becomes in an ON state in the second period; and

a comparison circuit whose input is connected to the node, the comparison circuit comparing the input voltage in the first period and the output voltage in the second period to output the comparison result voltage.

3. The capacitive load drive circuit according to claim 2, wherein the comparison circuit includes:

an inverter circuit;

a capacitive element provided between an input of the inverter circuit and the node; and

a switch for short-circuit that is provided between the input and an output of the inverter circuit and becomes in an ON state in the first period,

the capacitive element retains a difference between the input voltage and an inversion voltage of the inverter circuit in the first period, and in the second period, the inverter circuit outputs, as the comparison result voltage, a voltage in accordance with a voltage obtained by adding the inversion voltage to the difference between the output voltage and the input voltage.

4. The capacitive load drive circuit according to claim 1, wherein

in the first period, the drive control unit sets the charge control voltage and the discharge control voltage to levels at which the charge circuit and the discharge circuit do not operate, respectively, and in the second period, based on the comparison result voltage, the drive control unit sets the charge control voltage to a level at which the charge circuit operates when the output voltage is lower than the input voltage, and sets the discharge control voltage to a level at which the discharge circuit operates when the output voltage is higher than the input voltage.

5. The capacitive load drive circuit according to claim 4, wherein the drive control unit includes:

a charge-side amplifier circuit that outputs the charge control voltage to the charge circuit; and

a discharge-side amplifier circuit that outputs the discharge control voltage to the discharge circuit.

6. The capacitive load drive circuit according to claim 5, wherein the drive control unit further includes:

a charge-side capacitive element to capacitively-couple the output of the voltage comparison unit and an input of the charge-side amplifier circuit;

a discharge-side capacitive element to capacitively-couple the output of the voltage comparison unit and an input of the discharge-side amplifier circuit;

a charge-side setup switch that becomes in an ON state in the first period to supply an OFF voltage to the input of the charge-side amplifier circuit; and

a discharge-side setup switch that becomes in an ON state in the first period to supply an OFF voltage to the input of the discharge-side amplifier circuit.

7. The capacitive load drive circuit according to claim 1, wherein

as the charge circuit, the push-pull output unit includes a switch for charge that is provided between a high voltage-side power supply line and the output terminal, and is controlled using the charge control voltage, and

as the discharge circuit, the push-pull output unit includes a switch for discharge that is provided between a low voltage-side power supply line and the output terminal, and is controlled using the discharge control voltage.

8. The capacitive load drive circuit according to claim 7, wherein the push-pull output unit further includes:

a switch for charge stop that is provided between the high voltage-side power supply line and the output terminal in series with the switch for charge; and

a switch for discharge stop that is provided between the low voltage-side power supply line and the output terminal in series with the switch for discharge.

9. A display device that drives a signal line connected to a pixel circuit using a capacitive load drive circuit according to claim 1.