Liquid crystal display with separate positive and negative driving circuits
View Patent ↗The invention provides an active matrix type TFT LCD in which a driving voltage of pixel TFTs is reduced. A pixel is formed with two thin film transistors, i.e., a positive-voltage-applying n-channel TFT for applying a data voltage having a positive polarity to a pixel electrode and a negative-voltage-applying p-channel TFT for applying a data voltage having a negative polarity to the pixel electrode. A source electrode of the positive-voltage-applying TFT is connected to the pixel electrode; a drain electrode of the same is connected to a data bus line for applying the positive voltage; and a gate electrode of the same is connected to a gate bus line for applying the positive voltage. A source electrode of the other TFT is also connected to the pixel electrode; a drain electrode of the same is connected to a data bus line for applying the negative voltage; and a gate electrode of the same is connected to a gate bus line for applying the negative voltage.
1. A liquid crystal display comprising:
a liquid crystal capacitance formed by sandwiching a liquid crystal between electrodes facing each other;
a positive polarity driving circuit system for charging the liquid crystal capacitance with a positive charge by applying a voltage having a positive polarity between the electrodes; and
a negative polarity driving circuit system provided separately from the positive polarity driving circuit system for charging the liquid crystal capacitance with a negative charge by applying a voltage having a negative polarity between the electrodes;
wherein the electrodes facing each other have:
a pixel electrode provided at each of a plurality of pixels having the liquid crystal capacitance; and
a common electrode facing each of the pixel electrodes with the liquid crystal interposed therebetween to apply a common voltage thereto;
wherein the pixels have:
a positive-voltage-applying TFT for applying a voltage having the positive polarity to the pixel electrode; and a negative-voltage-applying TFT for applying a voltage having the negative polarity to the pixel electrode;
wherein a conductivity type of channels of the positive-voltage-applying TFT and the negative-voltage-applying TFT is the same;
wherein an operating range for a gate voltage of the positive-voltage-applying TFT is different from an operating range for a gate voltage of the negative-voltage-applying TFT;
wherein a potential to keep the positive-voltage-applying TFT off is different from a potential to keep the negative-voltage-applying TFT off; and
a potential difference between a potential to keep the positive-voltage-applying TFT on and the potential to keep the positive-voltage-applying TFT off is different from a potential difference between a potential to keep the negative-voltage-applying TFT on and the potential to keep the negative-voltage-applying TFT off.
2. A liquid crystal display according to claim 1 , wherein the positive polarity driving circuit system has:
a positive-voltage-applying gate bus line for outputting a positive-voltage-applying gate pulse to a gate electrode of the positive-voltage-applying TFT; and
a positive-voltage-applying data bus line for outputting a data voltage having the positive polarity to a source or drain electrode of the positive-voltage-applying TFT;
wherein the negative polarity driving circuit system has:
a negative-voltage-applying gate bus line for outputting a negative-voltage-applying gate pulse to a gate electrode of the negative-voltage-applying TFT; and
a negative-voltage-applying data bus line for outputting a data voltage having the negative polarity to a source or drain electrode of the negative-voltage-applying TFT.
3. A liquid crystal display according to claim 2 , wherein the positive polarity driving circuit system has:
a gate bus line driving circuit for positive polarity driving for outputting the positive-voltage-applying gate pulse to the positive-voltage-applying gate bus line; and
a data bus line driving circuit for positive polarity driving for outputting the data voltage having the positive polarity to the positive-voltage-applying data bus line;
wherein the negative polarity driving circuit system has:
a gate bus line driving circuit for negative polarity driving for outputting the negative-voltage-applying gate pulse to the negative-voltage-applying gate bus line; and
a data bus line driving circuit for negative polarity driving for outputting the data voltage having the negative polarity to the negative-voltage-applying data bus line.
4. A liquid crystal display according to claim 1 , wherein a conductivity type of channels of the positive-voltage-applying TFT and the negative-voltage-applying TFT is an n-type.
5. A liquid crystal display according to claim 1 , wherein a conductivity type of channels of the positive-voltage-applying TFT and the negative-voltage-applying TFT is a p-type.
6. A liquid crystal display according to claim 1 , wherein the positive polarity driving circuit system and the negative polarity driving circuit system are integrally formed on an insulated substrate on which either of the electrodes is formed.