Patent Publication Number: US-2007121263-A1

Title: Timing controller chip

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the priority benefit of Taiwan application serial no. 94141851, filed on Nov. 29, 2005. All disclosure of the Taiwan application is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a timing controller chip, and more particularly, to a timing controller chip with an electrical overstress (EOS) protection function.  
      2. Description of the Related Art  
      The timing controller is a major component in the driving circuit of the liquid crystal display (LCD) panel for providing the control signals to the source driver and the gate driver so as to correctly display the frame. Currently, the timing controller is usually assembled in a single chip, thus it is also known as a timing controller chip.  
      During the testing procedure of the printed circuit board (hereinafter “PCB”) in the fabricating process of the LCD panel, it is common that the low voltage differential signal (LVDS) input pins of the timing controller chip will be damaged by the EOS, resulting in permanent malfunction.  
       FIG. 1  schematically shows a circuit diagram of an LVDS input pin circuit  100  in a conventional timing controller chip. The chip is fabricated by a 0.18 μm 1.8V/3.3V 1 poly (poly-silicon)  5  metal logic process. The LVDS input pin circuit  100  comprises two electrostatic discharge (ESD) protection circuits ESD 1  and ESD 2 , and an operational amplifier OP, wherein each of the ESD circuits ESD 1  and ESD 2  is constituted by an n-channel metal oxide semiconductor field effect transistor (NMOS transistor). In addition, the output terminal o of the operational amplifier OP is electrically linked to an internal circuit of the timing controller chip.  
      The current vs. voltage relationship of the LVDS input pin circuit  100  is shown in  FIG. 2 . Specifically,  FIG. 2  shows a current vs. voltage diagram of the LVDS input pin INP or INN opposite to the ground. The measured value on the input pin INP is exactly the same as the measured value on the input pin INN, thus only one diagram is required. As shown in  FIG. 2 , the LVDS input pin circuit  100  can only endure an EOS of 7V. In other words, during the PCB testing process, as long as a surge higher than 7V is input to either the INP or INN, the transistors inside the corresponding ESD protection circuits and inside the operational amplifier OP are collapsed, which permanently damages the timing controller chip.  
      Since it is hard to ensure the EOS protection is perfectly performed on all of the testing tools and production environments distributed all over the world, if the EOS protection technique can be integrated into the chip, the poor yield rate in the assembly line and the manufacturing cost will be significantly reduced. Currently, there are two techniques to integrate the EOS protection into the timing controller chip, but both of them have the drawbacks.  
      The first technique uses a high-voltage enduring process. For example, more steps, such as increasing the thickness of the gate oxide and the low density ion doping to cover the transistor, are added in the fabricating process to raise the breakdown voltage of the transistor. Such technique complicates the fabricating process and increases the manufacturing cost. Moreover, the electrical property of the high-voltage enduring process is different from that of the logic process, thus the circuit has to be greatly modified.  
      The second technique uses a serial-connected ESD protection circuit. Such technique increases the layout area and reduces the capability of ESD protection. Although such technique can protect the ESD protection circuit, it cannot protect the transistors inside the operational amplifier OP.  
     SUMMARY OF THE INVENTION  
      Therefore, it is an object of the present invention to provide a timing controller chip. The timing controller chip provided by the present invention significantly reduces the poor yield rate in the assembly line and decreases the manufacturing cost by integrating the EOS protection technique to improve the EOS endurance. The timing controller chip with the original ESD protection capability is fabricated from the original fabricating process, such that the present invention can provide the EOS protection to both of the ESD protection circuit and the operational amplifier.  
      In order to achieve the object mentioned above and others, the present invention provides a timing controller chip. The timing controller chip comprises a first resistor, a second resistor, a first electrostatic discharge (ESD) protection circuit, a second ESD protection circuit, and an operational amplifier. Wherein, the first and the second resistors are electrically coupled to a first and a second low voltage differential signal (LVDS) input pins of the timing controller chip, respectively. The first and the second ESD protection circuits are electrically coupled to the first and the second resistors, respectively. Moreover, the operational amplifier has a non-inverting input terminal electrically coupled to the first resistor and the first ESD protection circuit, and an inverting input terminal is electrically coupled to the second resistor and the second ESD protection circuit.  
      In the timing controller chip according to an embodiment of the present invention, both of the first and second transistors are poly-silicon transistors. For example, they are n-channel poly-silicon transistors or p-channel poly-silicon transistors.  
      By integrating the EOS protection technique to improve the EOS endurance, the timing controller chip of the present invention significantly reduces the poor yield rate in the assembly line and greatly decreases the manufacturing cost without having to modify the equipment and flow of the assembly line. In the present invention, the timing controller chip mentioned above is slightly modified to add two additional resistors. With such new design, the original fabricating process can be used and the original ESD protection capability can be maintained. Accordingly, as described in the preferred embodiment of the present invention, the present invention can provide the EOS protection to both of the ESD protection circuit and the operational amplifier. 
    
    
     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  schematically shows a circuit diagram of an LVDS input pin circuit in a conventional timing controller chip.  
       FIG. 2  schematically shows a current vs. voltage diagram of the LVDS input pin opposite to the ground in a conventional timing controller chip.  
       FIG. 3  schematically shows a circuit diagram of an LVDS input pin circuit in a timing controller chip according to a preferred embodiment of the present invention.  
       FIG. 4  schematically shows a current vs. voltage diagram of the LVDS input pin opposite to the ground in a timing controller chip according to the preferred embodiment of the present invention.  
       FIG. 5  schematically shows a circuit diagram of the operational amplifier in  FIG. 3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 3  schematically shows a circuit diagram of an LVDS input pin circuit  300  in a timing controller chip according to a preferred embodiment of the present invention. The LVDS input pin circuit  300  comprises two resistors R 1  and R 2 , two ESD protection circuits ESD 1  and ESD 2 , and an operational amplifier OP. Wherein, the resistor R 1  is electrically coupled to an LVDS input pin INP of the timing controller chip. The resistor R 2  is electrically coupled to the other LVDS input pin INN of the timing controller chip. The ESD protection circuit ESD 1  is electrically coupled to the resistor R 1 , and the ESD protection circuit ESD 2  is electrically coupled to the resistor R 2 . A non-inverting input terminal (marked as “+”) of the operational amplifier OP is electrically coupled to the resistor R 1  and the ESD protection circuit ESDI, and an inverting input terminal (marked as “−”) is electrically coupled to the second resistor R 2  and the ESD protection circuit ESD 2 . Moreover, an output terminal of the operational amplifier is linked to an internal circuit of the timing controller chip.  
      Both of the resistors R 1  and R 2  in the present embodiment are poly-silicon resistors. For example, they are n-channel or p-channel poly-silicon transistors. Each of the ESD protection circuits ESD 1  and ESD 2  is constituted by an NMOS transistor, wherein a gate of each NMOS transistor is electrically coupled to a source of the NMOS transistor. The present invention does not limit the type of the ESD protection circuit, thus in other embodiments of the present invention, the ESD protection circuits EDS 1  and ESD 2  can be replaced with any type of existing ESD protection circuit. Moreover, the present invention does not limit the type of the operational amplifier, thus in other embodiment of the present invention, the operational amplifier OP can be replaced with any type of existing operational amplifier.  
      Comparing to the conventional configuration, only two additional resistors are added in the LVDS input pin circuit  300  of the present embodiment. Accordingly, the timing controller chip can be fabricated by the original fabricating process, for example, the 0.18 μm 1.8V/3.3V 1 poly (poly-silicon)  5  metal logic process mentioned above.  
       FIG. 4  schematically shows a current vs. voltage diagram of the LVDS input pin INP or INN opposite to the ground in  FIG. 3 . The measured value on the input pin INP is exactly the same as the measured value on the input pin INN, thus only one diagram is required. As shown in  FIG. 4 , the EOS endurance of the LVDS input pin circuit  300  is enhanced to 9.5V when R 1 =R 2 =100 ohm, enhanced to 11V when R 1 =R 2 =180 ohm, and enhanced to 14.5V when R 1 =R 2 =300 ohm. By appropriately controlling the resistances of the transistors R 1  and R 2 , the EOS endurance is improved, which alleviates the EOS damage on the LVDS input pin in the timing controller chip during the PCB testing process.  
       FIG. 5  schematically shows a circuit diagram of an operational amplifier in  FIG. 3 . The operational amplifier OP comprises a plurality of NMOS transistors N 1 , N 2 , N 3 , N 6 , N 7 , N 9 , N 10 , a plurality of PMOS transistors P 6 , P 7 , P 9 , P 10 , and an inverter INV 2 . Wherein, the input terminal IN of  FIG. 5  is exactly the non-inverting input terminal “+” of  FIG. 3 , the input terminal INB of  FIG. 5  is exactly the inverting input terminal “−” of  FIG. 3 , and the output terminal OUT of  FIG. 5  is exactly the output terminal “o” of  FIG. 3 . Here, the output terminal “o” is electrically connected to the internal circuit of the timing controller chip. The NMOS transistors N 1  and N 2  in the internal circuit of the operational amplifier OP and the ESD protection circuits ESD 1  and ESD 2  are the components which may be damaged by the EOS.  
      In summary, by integrating the EOS protection technique to improve the EOS endurance, the timing controller chip of the present invention significantly reduces the poor yield rate in the assembly line and greatly decreases the manufacturing cost without having to modify the equipment and flow of the assembly line. In the present invention, the timing controller chip mentioned above is slightly modified to add two additional resistors. With such new design, the original fabricating process can be used and the original ESD protection capability can be maintained. Accordingly, the present invention can provide the EOS protection to both of the ESD protection circuit and the operational amplifier.  
      Although the invention has been described with reference to a particular embodiment thereof, it will be apparent to one of the ordinary skills in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed description.