Patent Grant
8040312
This application claims the benefit of Taiwanese patent application serial No. 94107567, filed Mar. 11, 2005, the disclosure of which is incorporated herein by reference in its entirety.
The disclosure relates in general to liquid crystal displays, and more particularly, to chip-on-glass liquid crystal displays with unique circuit arrangement to reduce fabrication complexity and improve signal quality.
Liquid crystal displays (LCD) have become more and more popular for use in computer monitors or TVs due to light weight, flatness and low radiation. In addition to improving the display quality of LCDs, such as color, contrast and brightness, LCD manufacturers try to improve the manufacturing process to reduce cost and manufacturing time.
Generally, an LCD includes a timing controller, source drivers and at least one gate driver to drive its liquid crystal panel. in a conventional LCD, the timing controller is welded on a control print circuit board, the source drivers are welded on an X-board, and the gate driver is welded on a Y-board. The control print circuit board connects to the X-board via flexible printed circuit boards (FPCs), while the X-board and the Y board each connects to the liquid crystal panel via other FPCs. Therefore, the conventional LCD requires at least three boards connecting to the panel and hence the manufacturing process is complex. In order to simplify the manufacturing process, chip-on-glass (COG) LCDs are developed.
However, the manufacturing process of conventional COG LCDs is still complex because it still needs many flexible printed circuit boards. As shown in
Accordingly, there is a need for a COG LCD that further reduces the needed number of flexible printed circuit boards.
This disclosure proposes display devices with unique circuit arrangements that reduce the needed number of connecting points connecting circuits disposed on a glass substrate of the display devices and other circuits not disposed on the glass substrate. The display devices may be liquid crystal displays (LCDs) or other types of displays that use driving circuits, such as source drivers and/or gate drivers, for controlling the display of images.
An exemplary display includes a glass substrate, a plurality of serial-connected source drivers and at least one gate driver. The source drivers and the at least one gate driver are disposed on the glass substrate using, for example, chip-on-glass technology. The display further includes at least one flexible connector, such as a printed circuit board. Each of the at least one flexible connector corresponds to a selected one of the source drivers. The selected one of the source drivers is configured to receive image data and control information from the corresponded flexible connector, and convey the image data and the control information to at least one neighboring source driver. In one aspect, the at least one flexible connector is disposed in such a way that delays and distortions of the image data and the control information are acceptable to the source drivers.
According to one embodiment, the image data and control information are provided by a control circuit, such as timing controllers, not disposed on the glass substrate. The control circuit may be disposed on a circuit board coupling to the display via the at least one flexible connector.
An exemplary source driver according to this disclosure includes a first receiver and a second receiver, both configured to receive image data and control information, and a first transceiver and a second transceiver, both coupled to at least one neighboring source driver. A driving unit is provided to generate driving voltages based on the image data and the control information to drive the display. A bus switch selectively couples the first transceiver and the second transceiver. When the source driver is set to operate in a dual-way transmission mode, the first transceiver and the second transceiver are disconnected. The first transceiver receives the image data and the control information from the first receiver, and the second transceiver receives the image data and the control information form the second receiver. When the source driver is set to operate in a single-way transmission mode, the first transceiver and the second transceiver are connected. The image data and the control information received by the first transceiver are transmitted to the second transceiver.
Other objects, features, and advantages of the disclosure will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.
Each of the source drivers 212 has at least one of a first operation mode and a second operation mode. The source driver 212(3) and the source driver 212(8) are set to the first operation mode to execute a dual-way transmission. The source driver 212(3) and the source driver 212(8) each receives the image data and control signals from the timing controller 225 and transmits them to the neighboring source drivers at both the right side and the left side thereof. For example, the source driver 212(3) simultaneously transmits the image data and control signals to both the neighboring source drivers 212(2) and 212(4), which are located at the two sides of the source driver 212(3). The source drivers 212(1), 212(2), 212(4)-212(7), 212(9) and 212(10) are set to the second operation mode to execute a single-way transmission, and are not directly connected to the timing controller 225. The source drivers 212(1), 212(2), 212(4)-212(7), 212(9) and 212(10) each receives the image data and the control signals from the right (or left) source driver and transmits them to the left (or right) source driver. For instance, the source driver 212(2) receives the image data and the control signals from the source driver 212(3) on one side, and transmits them to the source driver 212(1) at the other side. In the embodiment, the LCD 200 is a big screen monitor having 10 source drivers and two flexible printed circuit board 230 and 232. The number of flexible printed circuit boards is not limited to two, as long as the distortions and delays of signals are acceptable.
In this embodiment, the source drivers are divided into a left group including source drivers 212(1)-212(5) and a right group including source drivers 212(6)-212(10). The flexible printed circuit board 230 connects to the center source drivers 212(3) of the left group, and the flexible printed circuit board 232 connects to the center source drivers 212(8) of the right group, such that the distortions and delays of signals, caused by the parasitic capacitance and resistance, are minimized. On the other hand, the source drivers can also be divided into more than three groups, and each of the groups directly connects to the timing controller via a flexible printed circuit board, so long as the distortions and delays of the signals are acceptable.
In another embodiment, the FPC 230 is connected to source driver 212(5), and FPC 232 is connected to source driver 212(6). All the source drivers are set to execute a single-way transmission. In operation, image data and control signals are conveyed to source drivers 212(5) and 212(6) via FPC 230 and FPC 232, respectively. Source Drivers 212(5) and 212(6) then provide the image data and control signals to other source drivers in the same group.
According to another embodiment, the source drivers 212 form only one driver group. The timing controller 225 is connected to a selected one of the source drivers via only one flexible printed circuit board. The selected source driver receives image data and control information from the timing controller 225 via the flexible printed circuit board, and transmits the image data and control information to other source drivers that are not directly connected to the flexible printed circuit board.
When the source driver start signal STH is asserted, the source drivers 212 start to prepare to receive data. After a period td1, the data enable signal DE is asserted such that the timing controller 225 starts to output the image data to the source drivers 212. The source drivers 212 generate the driving voltage based on the polarization designated by the polarization control signal POL, and then output the driving voltages to the panel 210 according to the load signal Tp.
In the conventional LCD 100, the control signals are outputted by the timing controller directly to each source driver 112 and the gate driver 114. Each control signal needs at least one wire to transmit the signals. Therefore, a plurality of wires are required. As a result of the increased number of wires, the control signals are subject to distortions and delays caused by the parasitic capacitance and resistance of the wires between the timing controller and the source drivers, and between the timing controller and the gate driver.
In the exemplary LCD 200, the timing controller 225 integrates the control signals into a control bitstream° C. and transmits it by a wire to the source drivers 212. For example, the control signals can be packed into a plurality of control packets, each representing an event relevant to a control signal. The timing controller 225 designates one of the source drivers 212 to receive the control packet by using a target identification. The target identification is, for example, included in the control packet for each source driver to identify. After receiving the control packet, the source drivers 212 decode the control packet to generate the control signal. Since only a limited number of source drivers is needed to connect to the timing controller, the number of wires required to transmit the control signals is significantly reduced.
Each of the source drivers 212 has an associated identification, such as a built-in identification code, for identifying whether a received control packet is for its own by comparing the target identification in the control packet with the built-in identification.
[Transmission Protocol of the Control Bitstream]
In an exemplary LCD of this disclosure, the timing controller 225 transmits the control bitstream C to the source driver via only one wire. The control bitstream C includes a plurality of control packets, each representing an event of a corresponding control signal, such as a pull high event or a pull low event. After receiving the control packet, the source driver 212 generates the corresponding control signal by pulling high or pulling low accordingly.
According to one embodiment, each control packet has 16 bits. Other numbers of data bits can be used. If the control packet is received by dual-edge sampling, it takes 8 clocks to read one control packet. In other words, the control signal generated by a pull high event and a pull low event must remain at high level for at least a duration of 8 clocks. The control signals POL, CPV, STV, OEV can each be generated by a pull high event and a pull low event. The control signals having a duration less than 8 clocks, such as control signals STH and TP, are generated by the STH event and the TP event, respectively. After receiving the STH event/TP event, the source driver pulls high the control signal STH/TP for a pre-determined period td2/tw1 and then pulls low the control signal STH/TP. The sampling method for receiving the control packet is not limited to dual-edge sampling. Other types of sampling, such as rising-edge sampling or falling-edge sampling, can also be used.
If the control packet includes a control field 312 recording the STH event, the corresponding data field 314 records the target identification. Assuming the source drivers 212(1)-212(10) have built-in identifications of 0x0001-0x1010, respectively. After receiving the control packet with a STH event, the source driver compares the target identification of the control packet with the built-in identification. Responsive to a match, the source driver pulls high the control signal STH, and then pulls low the control signal STH after a period td2.
As illustrated in
Control signals POL, STV and OEV are generated by a pull high event and a pull low event. A control packet with the control field 312 recording a pull high event, its data field 314 designates which signal is to be pulled high. A control packet with the control field 312 recording a pull low event, its data field 314 designates which signal is to be pulled low.
The control field 312 of a control pack may record an initialization event for setting several kinds of initialization, such as the fan out of the source drivers. Other kinds of events can also be represented by the control packets.
In the embodiment, only one wire is required to transmit the control bitstream C. Therefore, the number of wires connecting the timing controller and the source drivers are greatly reduced. Consequently, the layout of the circuit is simplified, and the stability is enhanced. In addition, the control bitstream C can integrate only a part of the control signals and leave other part of the control signals to be transmitted in independent wires. Although not all the control signals are integrated to the control bitstream, the number of wires is reduced.
[Source Drivers]
The bus switch 422 includes two switches SW1 and SW2. When the source driver, 212(3) or 212(8), operates at the first operation mode, the bus switch turns off the switches SW1 and SW2 such that the control transceiver 414 and 416 are disconnected and the data transceiver 424 and 426 are disconnected from each other. Thus, the control bitstream C1 and the image data D1 received by the receiver 410 are transmitted to the control transceiver 414 and the data transceiver 424, respectively, and the control bitstream C2 and the image data D2 received by the receiver 410 are transmitted to the control transceiver 416 and the data transceiver 426, respectively.
When a source driver, such as 212(1)-212(2), 212(4)-212(7), 212(9), or 212(10), operates in the second operation mode, the receivers 410 and 412 are disabled, and the bus switch turns on the switches SW1 and SW2 such that the transceivers 413 and 415 are connected to each other. Consequently, the data transceivers 424 and 426 are connected and the control transceivers 414 and 416 are connected. Thus, the source driver can transmit the control bitstream and the image data received to the next adjacent source driver in response to the designated transmission direction.
The wave generators 420 and 421 receive the control bitstreams C1 and C2, respectively, for generating source control signals S, such as STH(1), STH(2), POL(1), POL(2), TP(1), TP(2), etc., and the gate control signals G, such as CPV(1), CPV(2), STV(1), STV(2), OEV(1), OEV(2), etc. The control signals G are generated by one of the source drivers. In the LCD 200 shown in
When receiving the signal STH, the driving unit 434 starts to latch image data D for converting to analog driving voltages in response to the signal POL, and then transmits the analog driving signals to the panel 210 after receiving the load signal TP.
When a source driver operates in the first operation mode, such as source driver 212(3), the wave generators 420 and 421 are both activated to receive the control bitstreams C1 and C2, respectively, and generate the source control signals S and the gate control signals G. The control bitstream C1 and C2 are independent, and image data D1 and D2 are independent. On the other hand, if a source driver is set to operate in the second operation mode, such as source driver 212(2) or 212(4), the control bitstream C1 is the control bitstream C2, and the image data D1 is the image data D2. Accordingly, only one of the wave generators 420 and 421 is activated to generate the source control signals S and the gate control signals G. Other wave generators in the second-operation-mode source driver can be disabled, omitted or still activated to generate the source control signals S and the gate control signals G.
The signal generator 460 pulls high the corresponding signal after receiving the control item with a pull high event. The level of the pull-high signal is maintained until the signal generator 460 receives a corresponding control item with a pull low event.
However, the control signal is not suitable to be generated by the pull high event and the pull low event if the duration time of the high level of the control signal is less than 8 clocks, such as the control signal TP, since the wave generator needs 8 clocks to read a control packet.
In addition to being generated by the pull high event and the pull low event as described earlier, the gate control signals G can be generated according to the source control signals, such as STH or TP. For instance, the signal CPV may be generated according to the control signal STH. As illustrated in
After receiving the control item with the initialization event, the initiator 470 outputs a DC value to set the corresponding parameter.
An exemplary source driver of this disclosure reduces the control signal decay because the source control signal are generated by the source driver itself, not by the timing controller.
In addition, an exemplary LCD of this disclosure reduces the number of wires between the timing controller and the gate driver because the source driver generates the gate control signals and directly sends the signals to the gate driver via the wires on the glass substrate. The quality of the gate control signals are thus improved because the lengths of the transmission wires are reduced.
[Power Management]
In the power-saving mode, at least the power for data transceivers and the driving unit can be turned off. The data transceivers transmit the image data, which has large voltage swings and high frequency that increases power consumption. Thus, the power-saving convergent/divergent transmission methods can reduce unnecessary data transmission to save power. The power for the control transceivers of the source driver should not be turned off such that the source driver can still receive the control bitstream and operate responsively.
The convergent transmission method and the divergent transmission method can be applied at the same time. For example, the source drivers 212(1)-212(3) can use the convergent transmission method, while the source drivers 212(4)-212(5) use the divergent transmission method, or vice versa. Other modifications can be implemented by the ordinary skill in the art according to the disclosure.
While the disclosure has been described by way of example and in terms of a preferred embodiment, it is to be understood that the disclosure is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
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