Source driver and display device with protection unit

A source driver for driving a display panel and including a protection unit, a bias voltage generation unit and a buffer is provided. The protection unit detects a characteristic parameter of the source driver, and generates a switching signal according to a detection result. The bias voltage generation unit determines whether or not to provide a bias voltage according to the switching signal. The buffer is operated in the bias voltage so as to drive pixels in the display panel.

BACKGROUND

1. Field of the Invention

The invention relates to a source driver and a display device. Particularly, the invention relates to a source driver having an over current protection mechanism and a display device using the same.

2. Description of Related Art

FIG. 1is a structural schematic diagram illustrating a conventional liquid crystal display (LCD). Referring toFIG. 1, the conventional LCD100includes a display panel110, a plurality of source drivers121-126and a power controller130. The power controller130is disposed on a printed circuit board (PCB)140, and supplies power to the source drivers121-126through a resistor R1. The source drivers121-126are packaged on flexible circuit boards151-156through chip on flex (COF) bonding structures, and receive the power from the power controller130. In this way, the source drivers121-126can convert digital image data into corresponding driving voltages to drive pixels in the display panel110.

Moreover, in the conventional LCD100, an over current protection circuit160is generally disposed in the power controller130, and a main reason thereof is that during an assembling process of a LCD, poor wire bonding generally causes unnecessary short circuit between the wires. For example, during a packaging process of the source drivers121-126, originally independent output channels are probably connected due to the poor wire bonding. Now, the shorted output channels may cause the source drivers generating a large current to damage the internal circuit.

To avoid occurrence of the above problem, when the large current is generated, the over current protection circuit160can cut off the power supplied by the power controller130. In this way, all of the source drivers121-126stop operations, so as to avoid being damaged by the large current. However, although such over current protection method can protect the system, it also increases difficulty in testing of the display, since when the over current protection mechanism is activated, all of the source drives stop operations, so that it is hard for a testing engineer to determine the malfunctioned source driver or a block that has a connection problem. Now, the testing engineer has to perform testing to each of the source drivers and related connections of each of the blocks. Therefore, not only a time required for testing the display is increased, but also a labour cost is increased.

SUMMARY OF THE INVENTION

Accordingly, the invention is directed to a source driver, which can stop operation when an over current is generated, so as to reduce a time required for testing.

The invention is directed to a display device, which can position a source of short-circuit through flicking of a panel, so as to reduce a labour cost used for testing the display device.

The invention provides a source driver, which is used for driving a display panel, and includes a protection unit, a bias voltage generation unit and a buffer. The protection unit detects a characteristic parameter of the source driver, and generates a switching signal according to a detection result. The bias voltage generation unit determines whether or not to provide a bias voltage according to the switching signal. The buffer is operated in the bias voltage so as to drive pixels in the display panel.

In an embodiment of the invention, the bias voltage generation unit includes a bandgap reference circuit, a switch and a bias voltage circuit. The bandgap reference circuit provides a bandgap current. The switch has a first end and a second end. Moreover, the first end of the switch receives the bandgap current, and the switch determines whether or not to conduct the first end and the second end according to the switching signal. The bias voltage circuit is electrically connected to the second end of the switch, and generates the bias voltage when receiving the bandgap current.

In an embodiment of the invention, the protection unit includes an inverter, a voltage-dividing circuit, a sensing circuit and a comparator. The inverter receives the switching signal and generates an inverting signal of the switching signal. The voltage-dividing circuit generates a plurality of divided voltages according to a bandgap voltage non-related to temperature, and selects one of the divided voltages to serve as a reference voltage according to the switching signal and the inverting signal of the switching signal. The sensing circuit detects the characteristic parameter of the source driver, and generates a sensing voltage according to a detection result. The comparator compares the sensing voltage and the reference voltage, and generates the switching signal according to a comparison result.

According to another aspect, the invention provides a display device including a display panel and a source driver. The source dirtier includes a protection unit, a bias voltage generation unit and a buffer. The protection unit detects a characteristic parameter of the source driver, and generates a switching signal according to a detection result. The bias voltage generation unit determines whether or not to provide a bias voltage according to the switching signal. The buffer is operated in the bias voltage so as to drive pixels in the display panel.

According to the above descriptions, in the invention, the protection unit in the source driver is used to detect an over current, so that the source driver can automatically stop operation when the over current is occurred. In this way, the source driver causing the over current may lead to flicking of a certain block of the display panel. Therefore, a testing engineer can immediately position a source of shorted wires, so as to greatly reduce a time required for testing the display device and save a labour cost used for testing the display device.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

FIG. 2is a schematic diagram illustrating a display device according to an embodiment of the invention. Referring toFIG. 2, the display device200includes a display panel210, a plurality of source drivers221-226and a power controller230. The power controller230is disposed on a printed circuit board240, and the source drivers221-226are packaged on flexible circuit boards251-256through chip on flex (COF) bonding structures. During operation, the power controller230supplies power to the source drivers221-226. In this way, the source drivers221-226can convert digital image data into corresponding driving voltages to drive pixels (not shown) in the display panel210.

On the other hand, each of the source drivers221-226has a protection unit. Therefore, when poor wire bonding causes unnecessary short circuit, the source driver causing a large current may automatically stop operation, and the source drivers without causing the large current can normally operate. For example, when the source driver225generates the large current due to short circuit of the wires, the source driver225stops operating, while the other source drivers221-224and226can normally operate. Now, in the display panel210, a block A1driven by the source driver225produces flicker. Therefore, a testing engineer may perform testing to the source driver225and related connections of the block A1, so as to repair the display device200.

To fully convey the spirit of the invention to those skilled in the art, the source driver225is taken as an example for describing operations of the source driver.

FIG. 3is a schematic diagram illustrating a source driver according to an embodiment of the invention. Referring toFIG. 3, the source driver225includes a bias voltage generation unit310, a protection unit320and a plurality of buffers BF31-BF33. Moreover, the bias voltage generation unit310includes a bandgap reference circuit311, a bias voltage circuit312and a switch SW3. The protection unit320is electrically connected to the bandgap reference voltage311. A first end of the switch SW3is electrically connected to the bandgap reference circuit311, and a second end of the switch SW3is electrically connected to the bias voltage circuit312. The bias voltage circuit312is electrically connected to the buffers BF31-BF33.

In view of a whole operation, the bandgap reference circuit311generates a bandgap current IBGnon-related to temperature. The first end of the switch SW3receives the bandgap current IBG, and the switch SW3determines whether or not to conduct the first end and the second end according to a switching signal SCT. In this way, when the switch SW3is conducted, the bandgap current IBGis transmitted to the bias voltage circuit312, so that the bias voltage circuit312generates a bias voltage VRF. Comparatively, when the switch SW3is not conducted, the bias voltage circuit312cannot receive the bandgap current IBG, and accordingly cannot generate the bias voltage VRF.

On the other hand, the bandgap reference circuit311further generates a bandgap voltage VBGnon-related to temperature, so that the protection unit320can generate a plurality of divided voltages non-related to temperature according to the bandgap voltage VBG. Furthermore, the protection unit320detects a characteristic parameter of the source driver225, and generates the switching signal SCTaccording to a detection result, wherein the characteristic parameter is, for example, a temperature or a total current of the source driver225. Since he temperature of the source driver225is proportional to the total current thereof, the temperature or the total current of the source driver225can be used as a comparison parameter of an over current protection mechanism.

When the source driver225generates an over current due to short circuit of wires, i.e. when the temperature of the source driver225increases, the protection unit320generates the switching signal SCThaving a first logic level (for example, logic 1), so that the switch SW3cannot be conducted. In this way, the bias voltage circuit312cannot supply the bias voltage VRFto the buffers BF31-BF33, so that the source driver225cannot normally operate.

Moreover, the temperature or the total current of the source driver225can be slowly decreased as the source driver225stops the operation. When the temperature or the total current of the source driver225is decreased to a predetermined value, the protection unit320generates the switching signal SCThaving a second logic level (for example, logic 0), so that the switch SW3is conducted. Now, the bias voltage circuit312supplies the bias voltage VRFto the buffers BF31-BF33, so that the source driver225can normally drive the post-end pixels.

Similarly, when the source driver225again generates the over current, the protection unit320again turns off the bias voltage VRFsupplied by the bias voltage generation unit310, so as to again disables the source driver225. By repeatedly enabling/disabling the source driver225, the block A1driven by the source driver225produces flicker. Therefore, the testing engineer may perform testing to the source driver225and related connections of the block A1, so as to repair the display device200.

It should be noticed that in the present embodiment, the switch SW3is used to control a conducting path between the bandgap reference circuit311and the bias voltage circuit312, so that the bias voltage generation unit310can determine whether or not to provide the bias voltage VRFaccording to the switching signal SCT. However, during an actual application, those skilled in the art can also select the bias voltage generation unit310of a different structure according to the spirit of the invention.

For example, the switch SW3in the bias voltage generation unit310can be removed. Now, the bias voltage generation unit310can control the operation of the bandgap reference circuit311through the switching signal SCT. In this way, when the bandgap reference circuit311normally operates, the bias voltage generation unit310supplies the bias voltage V. Comparatively, when the bandgap reference circuit311stops operating, the bias voltage generation unit310cannot supply the bias voltage VRFto the buffers BF31-BF33.

To fully convey the operation of the source drive to those skilled in the art, the protection unit320and the bias voltage circuit312in the source driver225are respectively described in detail below.

FIG. 4is a schematic diagram illustrating a protection unit according to an embodiment of the invention. Referring toFIG. 4, the protection unit320includes a sensing circuit410, a voltage-dividing circuit420, a comparator430, an inverter440, a filter450and an amplifier460. The amplifier460receives a bandgap voltage VBGnon-related to temperature, and amplifies the bandgap voltage VBGand outputs it to the voltage-dividing circuit420. Moreover, the bandgap voltage VBGcan be provided by the bandgap reference circuit311in the bias voltage generation unit310.

Moreover, the voltage-dividing circuit420generates a plurality of divided voltages, for example, V41and V42according to the bandgap voltage VBG. In addition, the voltage-dividing circuit420selects one of the divided voltages V41and V42to serve as a reference voltage according to the switching signal SCTand an inverting signal /SCTof the switching signal SCT. The inverting signal /SCTof the switching signal SCTis generated by the inverter440. Here, an input terminal of the inverter440receives the switching signal SCT, and an output terminal of the inverter440generates the inverting signal /SCTof the switching signal SCTto the voltage-dividing circuit420.

On the other hand, the sensing circuit410detects the characteristic parameter of the source driver225, and generates a sensing voltage VTPaccording to a detection result. Moreover, an input terminal of the comparator430receives the sensing voltage VTP, and another input terminal of the comparator430receives the reference voltage (for example, V41or V42). In this way, the comparator430compares the sensing voltage VTPand the reference voltage (for example, V41or V42), and generates the switching signal SCTaccording to a comparison result.

Moreover, to increase an output characteristic of the protection unit320, a capacitor C4is electrically connected to the output of the voltage-dividing circuit420, and the filter450is connected behind the comparator430in series. In this way, the protection unit320can filter a noise of the switching signal SCTthrough the filter450, and then outputs the filtered switching signal SCTto the inverter440and the voltage-dividing circuit420.

FIG. 5is a timing diagram of the protection unit ofFIG. 4. How the protection unit320controls the logic level of the switching signal SCTis described with reference ofFIG. 4andFIG. 5. In the beginning, assuming the switching signal SCThas a state of logic 0, and the voltage-dividing circuit420outputs the divided voltage V41(for example, 1.8V) to serve as the reference voltage. Here, when the source driver225generates the over current due to short circuit of the wires, the sensing voltage VTPgenerated by the sensing circuit410is gradually increased. Moreover, at a time point t51ofFIG. 5, when the sensing voltage VTPis gradually increased and is greater than the divided voltage V41, the sensing voltage VTPis now greater than the reference voltage, so that the comparator430switches the state of the switching signal SCTto logic 1.

Moreover, the switching signal SCThaving the state of logic 1 is feedback to the voltage-dividing circuit420, so that the voltage-dividing circuit420reselects the divided voltage V42(for example, 0.8V) to serve as the reference voltage. On the other hand, the bias voltage generation unit310stops providing the bias voltage VRFaccording to the switching signal SCThaving the state of logic 1, so that the source driver225stops operating. Now, the current of the source driver225starts to decrease, and as the current of the source driver225is decreased, the sensing voltage VTPgenerated by the sensing circuit410is also decreased, continually.

Moreover, at a time point t52ofFIG. 5, when the sensing voltage VTPis continually decreased to be smaller than the divided voltage V42, the sensing voltage VTPis now smaller than the reference voltage, so that the comparator430switches back the state of the switching signal SCTto logic 0. In this way, the bias voltage generation unit310can supply the bias voltage VRFaccording to the switching signal SCThaving the state of logic 0, so that the source driver225can normally operate.

FIG. 6AandFIG. 6Bare schematic diagrams illustrating sensing circuits according to an embodiment of the invention. InFIG. 6A, the sensing circuit410includes a temperature sensor610. The temperature sensor610senses a temperature of the source driver225, and accordingly generates the sensing voltage VTP. In other words, the protection unit320determines whether the source driver225generates the over current by detecting the temperature of the source driver225.

On the other hand, as shown inFIG. 6B, the sensing circuit410includes a current sensor620and a current-to-voltage converter630. The current sensor620senses the total current of the source driver225, and accordingly generates a sensing current ITP. The current-to-voltage converter630converts the sensing current ITPinto the sensing voltage VTP. In other words, the protection unit320determines whether the source driver225generates the over current by detecting the total current of the source driver225.

FIG. 7is a schematic diagram illustrating a bias voltage circuit according to an embodiment of the invention. Referring toFIG. 7, the bias voltage circuit312includes N-channel transistors MN71-MN74and P-channel transistors MP71-MP72. A drain of the N-channel transistor MN71is electrically connected to the second end of the switch SW3for receiving the bandgap current IBG. Moreover, a gate of the N-channel transistor MN71is electrically coupled to the drain thereof. In addition, a drain of the N-channel transistor MN72is electrically connected to a source of the N-channel transistor MN71, a gate of the N-channel transistor MN72is electrically coupled to the drain thereof, and a source of the N-channel transistor MN72is electrically connected to ground.

Moreover, a gate of the N-channel transistor MN73is electrically connected to the gate of the N-channel transistor MN71. A drain of the N-channel transistor MN74is electrically connected to a source of the N-channel transistor MN73, a gate of the N-channel transistor MN74is electrically coupled to the gate of the N-channel transistor MN72, and a source of the N-channel transistor MN74is electrically coupled to ground.

Moreover, a source of the P-channel transistor MP71receives a power voltage VD, and a gate of the P-channel transistor MP71is electrically coupled to a drain thereof. A source of the P-channel transistor MP72is electrically connected to the drain of the P-channel transistor MP71, and a gate and a drain of the P-channel transistor MP72are electrically coupled to the drain of the N-channel transistor MN73.

The N-channel transistors MN71-MN74form a cascade current mirror. In this way, when the bandgap current IBGis supplied to the bias voltage circuit312, the current mirror copies the bandgap current IBG, and transmits it to the P-channel transistors MP71-MP72. Therefore, the bias voltage circuit312can generate the bias voltage VRFthrough the drain of the N-channel transistor MN73. Comparatively, when the bandgap current IBGcannot be supplied to the bias voltage circuit312, the bias voltage circuit312cannot operate, so that the bias voltage VRFis not generated.

In summary, in the invention, the protection unit in the source driver is used to detect the over current, so as to disable the operation of the source driver when the over current is occurred. In this way, when the poor wire bonding causes unnecessary short circuit, the source driver causing the large current can automatically stop operation, and the source drivers without causing the large current can normally operate. Therefore, the source driver causing the large current may lead to flicking of a certain block of the display panel. Therefore, the testing engineer can immediately position a source of the shorted wires, so as to greatly reduce a time required for testing the display device and save a labour cost used for testing the display device.