Patent Publication Number: US-7595658-B2

Title: Voltage divider circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation application of a prior application Ser. No. 11/163,854, filed Nov. 1, 2005. All disclosure of the US application is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a voltage divider circuit, and more particularly, to a voltage divider circuit adapted for a thin film transistor display (TFT LCD). 
   2. Description of Related Art 
   In the driving circuit for TFT LCDs, each source driver IC (integrated circuit) needs a set of DC voltages ranging from a low level to a high level, called a divided voltage.  FIG. 1  depicts a voltage divider circuit  100  implemented in a current notebook computer, wherein a voltage is first divided by a plurality of first resistors R 1  connected in series, and after the divided voltage passes through a buffer B consisting of operational amplifiers, the divided voltage is further divided into 10 voltage levels that range from V 1  (low voltage) to V 10  (high voltage) by a plurality of resistors R 2 . Next, these 10 voltage levels are input to the source driver ICs S 1 -S 8 . As the number of buffers B implemented in the circuit is small, manufacturing cost is accordingly lowered; however, the divided voltages are not easily adjusted because they are easily affected by the internal resistances in the source driver ICs S 1 -S 8 . 
   On the other hand,  FIG. 2  depicts a conventional voltage divider circuit  200  implemented in the current TFT LCD panel, wherein a voltage is divided by a plurality of first resistors R connected in series, and after the divided voltage passes through a buffer B,  18  divided voltages with voltage level ranging from V 1  TO V 18  are obtained and then input to the source driver ICs S 1 -S 10 . In addition, the voltage divider circuit  200  employs more buffers to overcome the drawbacks of the voltage divider circuit  100 , but the manufacturing cost is accordingly increased. 
   The objective of the present invention is directed to a voltage divider circuit that have the advantageous of the preceding two voltage divider circuits  100  and  200 . 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a voltage divider circuit capable of reducing a number of external components in the voltage divider circuit to lower the cost and power consumption. The voltage divider circuit is characterized in that the divided voltages can be easily adjusted without being affected by the internal resistance in the source driver ICs. 
   The present invention is further directed to provide a TFT LCD for decreasing the number of buffers implemented in a voltage divider circuit, thereby reducing cost and current consumption. 
   Based on the above objective and other objectives, the present invention provides a voltage divider circuit characterized in that the conventional external buffers connected between the DC voltage and the driver ICs are replaced by the built-in buffers in the source driver ICs. 
   In one embodiment, the voltage divider circuit comprises a plurality of resistors connected in series, a plurality of buffers and at least one source driver IC. In addition, a first terminal of the first resistor is electrically connected to a DC voltage and a first terminal of each of the remaining resistors is electrically connected to the second terminal of the previous resistor. The second terminal of the last resistor is grounded. The buffers and the resistors correspond with each other, wherein the first terminals of the resistors are electrically connected to their corresponding input terminals of the buffers and among these buffers, at least the first and the last buffers are rail-to-rail buffers. Moreover, the output terminals of buffers are electrically connected to the source driver ICs, wherein the each source driver IC contains one of the built-in buffers. 
   To achieve the above objective and other objectives, the present invention provides another TFT LCD that comprises a TFT LCD panel, a voltage divider circuit, a gate driver IC and a timing controller. Wherein the TFT LCD panel comprises a plurality of pixels, the voltage divider circuit comprises at least one source driver IC so as to provide divided voltages thereto, and replaces buffers originally required by the voltage divider circuit with the buffers comprised in the source driver IC. Moreover, the source driver IC outputs a voltage signal required for displaying pictures to the pixels. 
   On the other hand, a gate driver IC supplies pulse signals to the pixels so as to allow the pixels to receive the voltage signal output from the source driver IC. The timing controller provides signals required by the voltage divider circuit and the gate driver IC, and coordinates their operating timings. 
   The present invention employs the built-in buffers in each source driver IC to replace the buffers used in the conventional voltage divider circuit. Therefore, the number of external components in the conventional voltage divider circuit is reduced so as to lower cost. On the other hand, the built-in buffers in the source driver IC inherently consume power. The present invention does not increase power consumption, and further avoids power consumption in the external buffers in the conventional voltage divider circuit. Furthermore, the source driver ICs already have enough built-in buffers that receive one of the divided voltages in the present invention, such that the present invention is characterized in that divided voltages are easily adjusted without being affected by the internal resistance in the source driver ICs. 
   The objectives, other features and advantages of the invention will become more apparent and easily understood from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a conventional voltage divider circuit. 
       FIG. 2  is another conventional voltage divider circuit. 
       FIG. 3  is a voltage divider circuit of one embodiment of the present invention. 
       FIG. 4  schematically shows a TFT LCD of another embodiment of the present invention. 
   

   DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same parts. 
   The voltage divider circuit of the present invention is characterized in that the conventional buffers connected between the DC voltage and the driver ICs are replaced by the built-in buffers in the source driver ICs. The current source driver ICs have at least two built-in buffers serving as spare circuit during a repairing period. However, the small-size TFT LCD panel used in the notebooks has a high yield so that these built-in buffers are rarely used and can be used to replace the conventional external buffers in the conventional voltage divider circuit. In regard to a large-size TFT LCD panel used in a liquid crystal television, although it has a low yield, sufficient built-in buffers can be implemented in the voltage divider circuit as long as the source driver ICs with more built-in buffers are used. Hence, the present invention is suitable for a TFT LCD panel of any size. 
   In addition, to provide a precise divided voltage, the first one or two buffers (closest to the first divided voltage V 1 ) and the last one or two buffers (farthest away from the first divided voltage V 1 ), are rail-to-rail buffers. Since the built-in buffers in source driver ICs of the present invention are rail-to-rail buffers, they meet the preceding requirement. 
     FIG. 3  is a voltage divider circuit of one embodiment of the present invention. The voltage divider circuit  300  comprises 14 resistors connected in series, which are referred to as a first resistor (i.e. a resistor directly connected to the DC V 1 ), a second resistor, and so on; 10 source driver ICs S 1 -S 10 , and 20 built-in buffers B contained in 10 source driver ICs S 1 -S 10 . In this embodiment, each of the 10 source driver ICs S 1 -S 10  has two built-in buffers B. In addition, the first terminal of the first resistor R is electrically connected to a DC voltage V 1  and the first terminal of each of the remaining resistors is electrically connected to the second terminal of the previous resistor. The second terminal of the last resistor is grounded. The first 14 of all 20 built-in buffers B and the resistors correspond with each other, wherein the first terminals of the resistors are electrically connected to their corresponding input terminals of buffers. Moreover, the first 14 built-in buffers B are used while the rest are idle. 
   In this embodiment, the built-in buffers B serve to remove a parallel connection effect between the resistors R and the internal resistances in source driver ICs S 1 -S 10  so as to maintain the divided voltages V 1 -V 14  and promote their driving capability. All built-in buffers B are comprised of operational amplifiers; however, the operational amplifiers can be substituted by other devices with the same function. 
   In addition to providing the built-in buffers B, the source driver ICs S 1 -S 10  receive the divided voltages V 1 -V 14  from each built-in buffer B. The source driver ICs S 1 -S 10  serve to provide the voltage signals for pixel electrodes to display images in TFT LCD panels. 
   Note that the present invention is not limited to the number of resistors, source driver ICs, built-in buffers, rail-to-rail buffers or built-in buffers contained in each source driver IC. In addition, the numbers of the preceding described elements depend on a requirement of an application. For example, as shown in  FIG. 3 , the number of built-in buffers B is larger or equal to the number of the resistors. 
     FIG. 4  schematically shows a TFT LCD  400  of another embodiment of the present invention. The TFT LCD  400  comprises a TFT LCD panel  403 , the voltage divider circuit  300 , a gate driver IC  402  and a timing controller  401 . Wherein the TFT LCD panel  403  comprises a plurality of pixels, the voltage divider circuit  300  comprises ten source driver ICs S 1 -S 10  so as to provide divided voltages thereto, and replaces buffers originally required by the voltage divider circuit  300  with the buffers comprised in the source driver ICs S 1 -S 10 . Moreover, the source driver ICs S 1 -S 10  outputs a voltage signal required for displaying pictures to the pixels of the TFT LCD panel  403 . 
   On the other hand, a gate driver IC  402  supplies pulse signals to the pixels so as to allow the pixels to receive the voltage signal output from the source driver ICs S 1 -S 10 . The timing controller  401  provides signals required by the voltage divider circuit  300  and the gate driver IC  402 , and coordinates their operating timings. 
   In summary, the present invention employs the built-in buffers in each source driver IC to replace the buffers used in the conventional voltage divider circuit. Therefore, the number of external components in the conventional voltage divider circuit is reduced so as to lower cost. On the other hand, the built-in buffers inherently consume power. The present invention does not increase power consumption, but further avoids power consumed by the external buffers in the conventional voltage divider circuit. Furthermore, the source driver ICs already have enough built-in buffers that receive one of the divided voltages in the present invention, such that the present invention is characterized in that the divided voltages can be easily adjusted without being affected by the internal resistance in the source driver ICs. 
   In regard to saving the cost and power consumption, for example, in one embodiment of the present invention, originally four external operational amplifiers are used to provide 10 divided voltages. The absence of four operational amplifiers can save 0.16 watts. For a TFT LCD panel of 14.1 inches, the power-saving efficiency is 0.16 W/1.1 W=14%. Further, the present invention can lower the cost over the conventional voltage divider circuit. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.