Patent Publication Number: US-8525818-B2

Title: Display system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. application Ser. No. 12/370,585, filed on Feb. 12, 2009, which claims the benefit of U.S. provisional application No. 61/109,193, filed on Oct. 29, 2008, the contents thereof being incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display system, and more particularly, to a display system disposing a charge pump circuit on a flexible printed circuit (FPC) externally coupled to its display device for improving its voltage converting efficiency. 
     2. Description of the Prior Art 
     A charge pump is a type of DC to DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. Charge pumps use some form of switching devices to control the connection of voltages to the capacitor. The charge pumps can also double voltages, triple voltages, halve voltages, invert voltages, fractionally multiply or scale voltages such as × 3/2, × 4/3, ×⅔, etc. and generate arbitrary voltages, depending on the controller and circuit topology. A traditional charge pump circuit includes a voltage source, one or more charge capacitances, a load capacitance, a number of circuit switches and a fixed-frequency clock used to control the circuit switches. Using a clock period as an example (e.g. a doubled two phase circuit), in the first half period, circuit switches are used to make a parallel connection between a voltage source and a charge capacitance so as to charge the charge capacitance to a voltage level; in the second half period, circuit switches are used to make a serial connection between the voltage source and the charge capacitance and a load capacitance. After a number of periods are repeated, the voltage difference between two sides of the load capacitance will be lifted up to a voltage level that is much higher than that of the original voltage source. 
     In traditional small-sized and medium-sized thin-film transistor liquid crystal display (TFT-LCD) devices, with the growing size of the screen, the current consumption is also growing. If the charge pump circuit is disposed in the driving circuit of the TFT-LCD device, its voltage converting efficiency will get worse due to being limited by the indium tin oxide (ITO) resistors. 
     In addition, since the system end hopes to provide an input voltage ranging from 2.0V to 4.8V to the driving circuit of the TFT-LCD device directly, the charge pump circuit should be able to support a voltage converting ratio with different multiples (such as 1.5 times, 2 times, or 3 times) to provide the desired output voltage. Therefore, an important research and development subject in the industry is how to dispose a charge pump circuit in the TFT-LCD device without it being affected by the ITO resistors, and how to control the charge pump circuit. 
     SUMMARY OF THE INVENTION 
     It is therefore one of the objectives of the claimed invention to provide a display system disposing a charge pump circuit on a flexible printed circuit (FPC) externally coupled to its display device to solve the abovementioned problems. 
     According to an exemplary embodiment, a display system is provided. The exemplary display system includes a display device, a driving circuit, an FPC, a charge pump circuit and a control circuit. The driving circuit is disposed on the display device, for driving the display device. The FPC is externally coupled to the display device. The charge pump circuit is disposed on the FPC, for generating at least an output voltage to the driving circuit. The control circuit is disposed on the display device and coupled to the driving circuit, for generating a control signal to control the charge pump circuit. The charge pump circuit has a control pin coupled to the control circuit for receiving the control signal generated from the control circuit. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a display system according to an exemplary embodiment of the present invention. 
         FIG. 2  is a timing diagram illustrating a control signal, a clock signal and a process signal, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, hardware manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but in function. In the following discussion and in the claims, the terms “include”, “including”, “comprise”, and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. The terms “couple” and “coupled” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     In a case where the charge pump circuit is moved from the driving circuit of the thin-film transistor liquid crystal display (TFT-LCD) device to a flexible printed circuit (FPC), it is necessary to consider how to control operations of the charge pump circuit disposed on the FPC. Please refer to  FIG. 1 .  FIG. 1  is a diagram of a display system  100  according to an exemplary embodiment of the present invention. The display system  100  includes, but is not limited to, a display device  110 , a panel  120 , a driving circuit  130 , a control circuit  140 , a flexible printed circuit  150 , and a charge pump circuit  160 . The panel  120  is disposed on the display device  110 . The driving circuit  130  is disposed on the display device  110  for driving the panel  120 . The control circuit  140  is also disposed on the display device  110  and coupled to the driving circuit  130 , for generating a control signal SC to control the charge pump circuit  160 . The flexible printed circuit  150  is externally coupled to the display device  110 . The charge pump circuit  160  is disposed on the flexible printed circuit  150  for generating at least an output voltage to the driving circuit  130  according to the control signal SC generated by the control circuit  140 . 
     In this exemplary embodiment, the charge pump circuit  160  includes a control pin  162 , a charge pump unit  164 , a separating circuit  166  and a processing unit  168 . As shown in  FIG. 1 , the control pin  162  is coupled to the control circuit  140  for receiving the control signal SC generated from the control circuit  140 . In other words, there is only one control signal allowed to be transmitted from the control circuit  140  to the charge pump circuit  160  due to the fact that the charge pump circuit  150  is only equipped with a single pin for receiving one control signal. The charge pump unit  164  is used for generating at least the output voltage to the driving circuit  130 . The separating circuit  166  is coupled to the control pin  162 , for deriving a clock signal S clock  and a process signal S process  from the received control signal SC, wherein the process signal S process  can be a data signal S data  or a command signal S command . The processing unit  168  is coupled between the separating circuit  166  and the charge pump unit  164 , for receiving the clock signal S clock  and the process signal S process  generated from the separating circuit  166  and controlling the charge pump unit  164  according to the clock signal S clock  and the process signal S process . The charge pump circuit  160  sets a pumping factor PF 1  and generates two output voltages VSP and VSN according to the control signal SC, wherein the output voltages VSP and VSN are transmitted to the driving circuit  130  for usage. 
     In addition, the separating circuit  166  in this embodiment includes a low pass filter  1662  and a high pass filter  1664 . The low pass filter  1662  is coupled to the control pin  162 , for filtering the control signal SC to generate the clock signal S clock . The high pass filter  1664  is coupled to the control pin  162 , for filtering the control signal SC to generate the process signal S process . Please note that, in this embodiment, the separating circuit  166  utilizes two filters to derive the clock signal S clock  and the process signal S process  from the control signal SC, but this should not be taken as a limitation of the present invention. In other words, the separating circuit  166  can derive the clock signal S clock  and the process signal S process  by utilizing other kinds of circuits, depending upon the actual design considerations. Operations of the control circuit  140  and the charge pump circuit  160  will be detailed using certain figures and embodiments. 
     Please note that, for clarity and simplicity, this embodiment of the present invention will be described in detail with reference to the accompanying drawings. It is to be noted, however, that the present invention is not limited thereto. Please refer to  FIG. 2  in conjunction with  FIG. 1 .  FIG. 2  is a timing diagram illustrating a control signal SC, a clock signal S clock  and a process signal S process , respectively. The control circuit  140  generates the control signal SC to control the charge pump circuit  160  according to the requirements of the driving circuit  130 . In this embodiment, the control circuit  140  combines the process signal S process  transmitted with a high frequency and the clock signal S clock  transmitted with a related low frequency into the control signal SC as shown in  FIG. 2 . However, the present invention is not limited thereto. 
     The separating circuit  166  of the charge pump circuit  160  receives the control signal SC via the control pin  162 . The low pass filter  1662  and the high pass filter  1664  filter the received control signal SC to generate the clock signal S clock  and the process signal S process  shown in  FIG. 2 , respectively. Then, the high pass filter  1664  of the separating circuit  166  selectively generates the data signals S data  or the command signals S command  according to a carrier position of a high-frequency signal component of the control signal SC. For example, the high-frequency signal component of the control signal SC positioned at the high frequency of the clock signal S clock  is regarded as the data signal S data  (e.g., the logic value “0110” shown in  FIG. 2 ); the high-frequency signal component of the control signal SC positioned at the low frequency of the clock signal S clock  is regarded as the command signal S command  (e.g., the logic value “1011” shown in  FIG. 2 ). The charge pump circuit  160  can set the pumping factor PF 1  and generate the two output voltages VSP and VSN according to the clock signal S clock  and the process signal S process . For example, in this embodiment, the charge pump circuit  160  sets the pumping factor PF 1  to 3/2 according to the command signal S command  with logic value “1011”. 
     As can be seen from  FIG. 1 , the charge pump circuit  160  is disposed on the flexible printed circuit  150 , rather than being disposed in the driving circuit  130  of the display device  110 . Therefore, the voltage converting efficiency of the charge pump circuit  160  can be substantially improved due to its not being limited by the indium tin oxide (ITO) resistors R. Furthermore, only one control signal SC is needed to control the voltage converting ratio of the charge pump circuit  160 , which minimizes the pin number (pin count) of the charge pump circuit  160  to achieve a goal of lowering cost. Please note that the abovementioned display device  110  can be a TFT-LCD device and the driving circuit  130  can be a TFT-LCD driver IC, but this should not be construed as a limitation of the present invention. Besides, all of the devices implemented in the charge pump circuit  160  can be integrated in a single IC (e.g., System-on-a-chip, SoC), therefore, the charge pump unit  164  can supply an output voltage more precisely. 
     The abovementioned embodiments are presented merely for describing features of the present invention, and in no way should be considered to be limitations of the scope of the present invention. In summary, the present invention provides a display system disposing a charge pump circuit on an FPC externally coupled to its display device for improving its voltage converting efficiency. The display system of the present invention utilizes a single control pin and a control signal to control the charge pump circuit disposed on the FPC. Therefore, the voltage converting efficiency of the charge pump circuit in this display system will not be limited by the indium tin oxide (ITO) resistors. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.