1254912 九、發明說明： 【發明所屬之技術領域】 且特別是有關於一 本發明是有關於一種液晶顯示器 種液晶顯示器殘影改善電路。 【先前技術】 、近年來光電相關技術不斷地推陳出新，加上數位 代的到來’進而推動了液晶顯示器市場的蓬勃發展。液晶 顯不器具有高畫質、體積小、重量輕、低驅動電壓、盥低 消耗功率等優點’因此被廣泛應用於個人數位助理（pda)-、 行動電話、攝錄放影機、筆記型電腦、桌上型顯示器、車 用顯示器、及投影電視等消f性通訊或電子產品，並逐漸 取代陰極射線管而成為顯示器的主流。 液晶顯示器通常係使用殘影改善電路來改善關機時的 殘影現象’其原理係在關機時以控制訊號(xao)透過殘影改 。電路強迫閘極驅動器所有的閘極輸出⑽U丁)為閘極高 準位’因而打開所有的薄膜電晶體開關，以加速液晶上殘 存電壓之放電時間。 一第1圖係、、、曰7F白知殘影改善電路之電路圖。在液晶顯 丁-關機日$，電壓債測電路（未綠示）會將控制訊號由 原本的高電位（VDD)轉變為接地電位（GND)。如帛1圖所 示，當控制訊號XAQ變為低電位時，起始p型電晶體… 會由關變開，電晶體如則由開斷關。接著依此類推，電晶 體Q4、電晶體Q5、電晶體Q8會由關變開，而電晶體q3、 1254912 電晶體Q6、電晶體Q7則由開變關，使節點B之電位等於 閘極低電位（VGL)，再經電晶體Q9以及Q1〇之反相而使得 閘極輸出YOUT變為閘極高電位（vgh)。如此，即可打開 所有的薄膜電晶體開關，以加速液晶上殘存電壓之放電時 間。 然而，由於此時控制訊號χΑ0為接地電位（GND)，因 此虽連接於起始P型電晶體Q1源極之高電位（VDD)因關機 而下降低於電晶體之臨界電壓（vth)時，起始p型電晶體Q1 會由開轉變為關，因而導致節點A處於浮接（floating)狀 悲，無法確保閘極輸出γ〇υτ維持在閘極高電位（VGH)。 也就是說，當高電位（VDD)之電壓降至約lv時，此時 起始Ρ型電晶體Q1閘極導通電壓不足（Vgs < Vth)，導致作 為準位位移（level shift)之起始p型電晶體Q i的輸出電位浮 接。右疋殘影改善電路的内部節點因寄生電容效應而耦合 到錯误電位，則將產生輸出誤動作，閘極輸出會因 誤動作由閘極高電位（VGH)轉態為閘極低電位（VGL)，因此 無法消除液晶顯示器關機時的殘影現象。 【發明内容】 因此本發明就是提供一種液晶顯示器之殘影改善電 路，用以確保起始p型電晶體保持在導通狀態，避免前述 之浮接問題，使殘影改善電路之閘極輸出在液晶顯示器關 機後還是能夠保持在閘極高準位（VGH)。 依照本發明一較佳實施例，此殘影改善電路具有一起 1254912 始p型電晶體以及複數個電晶體。起始p型電晶體之閘極 連接^工制成號，此控制訊號在液晶顯示器關機後藉由起 始p型電晶體使該些電晶體產生一閘極高準位，用以導通 孩液S曰顯示器之薄膜電晶體以加速液晶上殘存電壓之放電 時間。此殘影改善電路特徵在於更包含一電壓選擇電路。 此電壓選擇電路在液晶顯示器關機後將控制訊號轉換為負 電壓準位，以確保起始p型電晶體能夠保持在導通狀態。 此殘影改善電路可改善原來使用接地電位作為控制訊 號XAO的缺點，即避免準位位移會因高電位（vdd)隨液晶 顯示器下降而產生誤動作的狀況。利用此殘影改善電路可 在關機時中和液晶電壓，加速殘存電壓的放電時間，以改 善液晶顯示器關機時的殘影現象。 【實施方式】 第2圖係繪示本發明之一較佳實施例之電路功能方塊 圖。此殘影改善電路200包含一電壓偵測電路2〇2、一電壓 選擇電路204以及一電壓轉換電路2〇6。電壓偵測電路2〇2 偵測液晶顯示器是否關機，並產生開關選擇訊號。電壓選 擇電路204根據開關選擇訊號產生控制訊號xa〇_new。 電壓轉換電路206包含起始P型電晶體以及複數個電晶 體，其中起始p型電晶體係由控制訊號xa〇—new控制其 開關。 複數個電晶體電性連接起始p型電晶體，在液晶顯示 器關機後，控制訊號XA0_NEW藉由起始p型電晶體使該 1254912 些電晶體產生閘極高準位VGH，用以導通液晶顯示器之薄 膜電晶體（未繪示），以加速液晶上殘存電壓之放電時門。而 且’電壓選擇電路204在液晶顯示器關機後將控制訊號 XAO一NEW轉換為負電壓準位，以確保起始p型電晶體保 持在導通狀態。 電壓偵測電路202偵測液晶顯示器之高電位（vdd)的 電壓，以判斷其是否關機並依此產生一開關選擇訊號。舉 例來說，當液晶顯示器未關機時，電壓偵測電路2〇2所產 生之開關選擇訊號係為一高電位（VDD)，而當液晶顯示器關 機時’電壓伯測電路202所產生之開關選擇訊號則為一低 電位（GND)。在實際操作上，當高電位（VDD)下降至預設的 偵測電壓時，此電壓偵測電路202將開關選擇訊號由高電 位（VDD)轉變為低電位（GND) ’以供通知之後的電壓選擇電 路 204。 第3圖則繪示此電壓選擇電路204之細部電路圖。如 第3圖所示，電壓選擇電路204利用電阻及r2將接地 電位（GND)及閘極低電位（VGL)作分壓來產生負電壓準 位，並根據開關選擇訊號選擇地輸出具有負電壓準位或是 正電壓準位之控制訊號XAO_NEW。 更具體地說，當液晶顯示器未關機時，電壓選擇電路 204將控制訊號XAO—NEW維持在正電壓準位，例如高電 位（VDD)，以確保起始P型電晶體（^1保持在關閉狀態。另 一方面，在液晶顯示器關機後，電壓選擇電路2〇4根據開 關選擇訊號之指示，將控制訊號XA0—NEW轉換為上述分 1254912 堡所得之負電壓準位，以確保起始p型電晶體qi 通狀態。 守 由上述可知，此較佳實施例中之負電壓準位係由接地 電位（GND)及閑極低電位（VGL)分麼所獲得，因此其電遷值 應介於接地電位（GND)及閘極低電位者之間。更明 確地說，當連接於起始P型電晶體Q1源極之高電位（VDD) 因關機而下降低於電晶體之臨界電壓（Vth)時，此負電壓準 位應使起始P型電晶體Q1閘極導通電壓大於電晶體之臨界 電壓（VgS>Vth)，以確保起始p ^電晶體φ在液晶顯示器 關機後能夠保持在導通狀態。因此，根據本發明之其他實 施例’此負電壓準位並不限於此範圍之間，可為閘極低電 位（VGL)或其他負電壓值。 第4圖則繪示此電壓轉換電路2〇6之細部電路圖。藉 由上述電壓選擇電路204，用以控制起始p型電晶體Q1之 開關的控制訊號XAO 一 NEW，可確保起始p型電晶體卩丨在 液晶顯不器關機後保持在導通狀態。因此，當控制訊號 XAO一NEW因關機由原本的高電壓準位（例如高電位vdd) 轉變負電壓準位時，起始P型電晶體Q1會由關變開，電晶 體Q2則由開斷關。 接著依此類推’電晶體q4、電晶體q5、電晶體Q8會 由關變開，而電晶體Q3、電晶體Q6、電晶體Q7則由開變 關，使節點B之電位等於閘極低電位（VGL)，再經電晶體 Q9以及Q10之反相而使得閘極輸出γ〇υτ變為閘極高電位 (VGH)。如此，即可打開所有的薄膜電晶體開_，以加速液 1254912 晶上殘存電壓之放電時間。 此殘影改善電路細係改善原來使用接地電位作為控 制訊號XAO的缺點，即避免準位位移會因高電位（卿)隨 液曰曰顯不态下降而產生誤動作的狀況。利用此殘影改善電 路可在關機時中和液晶電M，加速殘存電壓的放電時間， 以改善液晶顯示器關機時的殘影現象。 此殘影改善電路2〇〇可整合於單一晶片中，例如内建 於閘極驅動積體電路中，或是分散於液晶顯示器中之數 個相互電性連接之不同電路部分。再者，此殘影改善電路 〇〇僅為本發明之一較佳實施例，習知技藝者應理解實際應 用時當可依照規格與需要對其中各部分電路作適當的修改 與設計。亦即，其他藉由負電壓準位以確保起始P型電晶 體在關機後保持在導通狀態的殘影改善電路，也應符合本 發明之精神與範圍。 雖然本發明已以一較佳實施例揭露如上，然其並非用 以限疋本發明，任何熟習此技藝者，在不脫離本發明之精 神和範圍内，當可作各種之更動與潤飾，因此本發明之保 濩範圍當視後附之申請專利範圍所界定者為準。 【圖式簡單說明】 為讓本發明之上述和其他目的、特徵、優點與實施例 月匕更明顯易懂，所附圖式之詳細說明如下： 第1圖係繪示習知殘影改善電路之電路圖； 第2圖係繪示本發明之一較佳實施例之電路功能方塊 1254912 圖； 第3圖則繪示此電壓選擇電路之細部電路圖；以及 第4圖則繪示此電壓轉換電路之細部電路圖。 【主要元件符號說明】 Q1 :起始P型電晶體 Q2〜Q10 :電晶體 200 :殘影改善電路 202 :電壓偵測電路 204 :電壓選擇電路 206 :電壓轉換電路 Rl、R2 :電阻1254912 IX. Description of the Invention: [Technical Field of the Invention] In particular, the present invention relates to a liquid crystal display residual image improving circuit for a liquid crystal display. [Prior Art] In recent years, optoelectronic related technologies have been continuously introduced, and the arrival of digital generation has promoted the vigorous development of the liquid crystal display market. The liquid crystal display has the advantages of high image quality, small size, light weight, low driving voltage, low power consumption, etc., so it is widely used in personal digital assistants (PDAs), mobile phones, video recorders, notebooks. Computers, desktop monitors, car monitors, and projection TVs have gradually replaced the cathode ray tubes and become the mainstream of displays. Liquid crystal displays usually use the afterimage improvement circuit to improve the image sticking phenomenon during shutdown. The principle is to change the residual signal through the control signal (xao) when the computer is turned off. The circuit forces all gate outputs (10) of the gate driver to a gate high level' thus opening all of the thin film transistor switches to accelerate the discharge time of the residual voltage on the liquid crystal. A first diagram of the system diagram of the system, the 曰7F, and the image-removing circuit. On the LCD display - shutdown date, the voltage debt measurement circuit (not shown) will change the control signal from the original high potential (VDD) to the ground potential (GND). As shown in Fig. 1, when the control signal XAQ goes low, the starting p-type transistor... will be turned off, and the transistor will be turned off. Then, according to the analogy, the transistor Q4, the transistor Q5, and the transistor Q8 will be turned off, and the transistors q3, 1254912, the transistor Q6, and the transistor Q7 will be turned on and off, so that the potential of the node B is equal to the gate low. The potential (VGL) is then inverted by the transistors Q9 and Q1, causing the gate output YOUT to become a gate high potential (vgh). In this way, all of the thin film transistor switches can be turned on to accelerate the discharge time of the residual voltage on the liquid crystal. However, since the control signal χΑ0 is the ground potential (GND) at this time, although the high potential (VDD) connected to the source of the starting P-type transistor Q1 drops below the threshold voltage (vth) of the transistor due to shutdown, The starting p-type transistor Q1 will change from on to off, thus causing node A to be floating, and cannot ensure that the gate output γ 〇υτ is maintained at the gate high potential (VGH). That is to say, when the voltage of the high potential (VDD) drops to about lv, the gate-on voltage of the starting germanium transistor Q1 is insufficient (Vgs < Vth), resulting in a level shift. The output potential of the initial p-type transistor Q i is floated. If the internal node of the right-hand residual image improving circuit is coupled to the error potential due to the parasitic capacitance effect, an output malfunction will occur, and the gate output will be switched from the gate high potential (VGH) to the gate low potential (VGL) due to malfunction. Therefore, it is impossible to eliminate the image sticking phenomenon when the liquid crystal display is turned off. SUMMARY OF THE INVENTION Therefore, the present invention provides a residual image improving circuit for a liquid crystal display to ensure that the initial p-type transistor is maintained in a conducting state, avoiding the aforementioned floating connection problem, and causing the gate of the afterimage improving circuit to be outputted in the liquid crystal. The display can remain at the gate high level (VGH) after the display is turned off. In accordance with a preferred embodiment of the present invention, the afterimage enhancement circuit has a 1254912 initial p-type transistor and a plurality of transistors. The gate connection of the starting p-type transistor is made into a number, and the control signal causes the transistors to generate a gate high level by starting the p-type transistor after the liquid crystal display is turned off, for turning on the child fluid. The thin film transistor of the S曰 display accelerates the discharge time of the residual voltage on the liquid crystal. The afterimage improvement circuit is characterized by further comprising a voltage selection circuit. The voltage selection circuit converts the control signal to a negative voltage level after the liquid crystal display is turned off to ensure that the starting p-type transistor can remain in an on state. This afterimage improving circuit can improve the original use of the ground potential as the control signal XAO, that is, the positional displacement is prevented from being malfunctioning due to the high potential (vdd) falling with the liquid crystal display. The residual image improving circuit can neutralize the liquid crystal voltage during shutdown and accelerate the discharge time of the residual voltage to improve the image sticking phenomenon when the liquid crystal display is turned off. [Embodiment] FIG. 2 is a block diagram showing the function of a circuit according to a preferred embodiment of the present invention. The afterimage improving circuit 200 includes a voltage detecting circuit 2〇2, a voltage selecting circuit 204, and a voltage converting circuit 2〇6. The voltage detecting circuit 2〇2 detects whether the liquid crystal display is turned off and generates a switch selection signal. The voltage selection circuit 204 generates a control signal xa 〇 _new based on the switch selection signal. The voltage conversion circuit 206 includes an initial P-type transistor and a plurality of transistors, wherein the starting p-type transistor system controls its switching by a control signal xa 〇 - new. A plurality of transistors are electrically connected to the starting p-type transistor. After the liquid crystal display is turned off, the control signal XA0_NEW causes the 1254912 transistors to generate a gate high level VGH by turning on the p-type transistor to turn on the liquid crystal display. A thin film transistor (not shown) to accelerate the discharge time gate of the residual voltage on the liquid crystal. Moreover, the voltage selection circuit 204 converts the control signal XAO-NEW to a negative voltage level after the liquid crystal display is turned off to ensure that the starting p-type transistor remains in the on state. The voltage detecting circuit 202 detects the high potential (vdd) voltage of the liquid crystal display to determine whether it is turned off and generates a switch selection signal accordingly. For example, when the liquid crystal display is not turned off, the switch selection signal generated by the voltage detecting circuit 2〇2 is a high potential (VDD), and when the liquid crystal display is turned off, the switch selection generated by the voltage test circuit 202 is selected. The signal is a low potential (GND). In actual operation, when the high potential (VDD) drops to a preset detection voltage, the voltage detection circuit 202 changes the switch selection signal from a high potential (VDD) to a low potential (GND) for notification. Voltage selection circuit 204. FIG. 3 is a detailed circuit diagram of the voltage selection circuit 204. As shown in FIG. 3, the voltage selection circuit 204 divides the ground potential (GND) and the gate low potential (VGL) by a resistor and r2 to generate a negative voltage level, and selectively outputs a negative voltage according to the switch selection signal. The control signal XAO_NEW of the standard or positive voltage level. More specifically, when the liquid crystal display is not turned off, the voltage selection circuit 204 maintains the control signal XAO_NEW at a positive voltage level, such as a high potential (VDD), to ensure that the initial P-type transistor (^1 remains off) On the other hand, after the liquid crystal display is turned off, the voltage selection circuit 2〇4 converts the control signal XA0—NEW to the negative voltage level obtained by the above-mentioned 1254912 according to the indication of the switch selection signal to ensure the initial p-type. The transistor is in the PASS state. As can be seen from the above, the negative voltage level in the preferred embodiment is obtained by the ground potential (GND) and the idle low potential (VGL), so the electromigration value should be between Between the ground potential (GND) and the gate low potential, more specifically, when the high potential (VDD) connected to the source of the starting P-type transistor Q1 drops below the threshold voltage of the transistor due to shutdown (Vth When the negative voltage level is such that the gate-on voltage of the starting P-type transistor Q1 is greater than the threshold voltage of the transistor (VgS > Vth), to ensure that the initial p ^ transistor φ can remain after the liquid crystal display is turned off. Turn-on state. Therefore, according to Other embodiments of the invention 'This negative voltage level is not limited to this range, and may be a gate low potential (VGL) or other negative voltage value. Fig. 4 shows a detailed circuit diagram of the voltage conversion circuit 2〇6 The control signal XAO_NEW for controlling the switch of the starting p-type transistor Q1 is controlled by the voltage selection circuit 204 to ensure that the initial p-type transistor 保持 remains in the on state after the liquid crystal display is turned off. Therefore, when the control signal XAO-NEW is turned from the original high voltage level (for example, high potential vdd) to the negative voltage level due to shutdown, the initial P-type transistor Q1 will be turned off, and the transistor Q2 will be turned off. Then, etc., 'the transistor q4, the transistor q5, and the transistor Q8 will be turned off, and the transistor Q3, the transistor Q6, and the transistor Q7 will be turned on and off, so that the potential of the node B is equal to the gate. The low potential (VGL), which is reversed by the transistors Q9 and Q10, causes the gate output γ〇υτ to become the gate high potential (VGH). Thus, all the thin film transistors can be turned on to accelerate the liquid. 1254912 The discharge time of the residual voltage on the crystal. This afterimage improvement circuit is fine. The disadvantage of using the ground potential as the control signal XAO is improved, that is, the situation that the displacement of the level is prevented from being malfunctioning due to the high potential (clear) and the liquid level is reduced. The residual image improving circuit can be neutralized during shutdown. The liquid crystal M accelerates the discharge time of the residual voltage to improve the image sticking phenomenon when the liquid crystal display is turned off. The afterimage improving circuit 2 can be integrated into a single wafer, for example, built in a gate driving integrated circuit, or It is a plurality of different circuit parts that are electrically connected to each other in the liquid crystal display. Moreover, the image sticking improvement circuit is only a preferred embodiment of the present invention, and those skilled in the art should understand that when practical applications Properly modify and design each part of the circuit according to the specifications and needs. That is, other afterimage improving circuits that ensure a starting P-type transistor to remain in an on state after being turned off by a negative voltage level are also in accordance with the spirit and scope of the present invention. Although the present invention has been described above in terms of a preferred embodiment, it is not intended to limit the invention, and it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the present invention is defined by the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS In order to make the above and other objects, features, advantages and embodiments of the present invention more obvious and obvious, the detailed description of the drawings is as follows: FIG. 1 is a diagram showing a conventional image sticking improvement circuit. 2 is a circuit diagram of a circuit function block 1254912 in accordance with a preferred embodiment of the present invention; FIG. 3 is a detailed circuit diagram of the voltage selection circuit; and FIG. 4 is a circuit diagram of the voltage conversion circuit. Detailed circuit diagram. [Description of main component symbols] Q1: Initial P-type transistor Q2~Q10: Transistor 200: Afterimage improvement circuit 202: Voltage detection circuit 204: Voltage selection circuit 206: Voltage conversion circuit Rl, R2: Resistor
1111