TWI866692B - Display driver chip, liquid crystal display and information processing device capable of avoiding flickering phenomenon at the initial stage of awakening - Google Patents

Abstract

A display driver chip that can avoid flickering in the early stage of awakening has a first floating detection circuit and a second floating detection circuit to detect the input status of a positive analog voltage input terminal and a negative analog voltage input terminal, and when the input status is detected to be floating, the positive analog voltage input terminal and the negative analog voltage input terminal are grounded, thereby avoiding flickering on the liquid crystal screen when the system is awakened.

Description

Display driver chip, liquid crystal display and information processing device capable of avoiding flickering phenomenon at the initial stage of awakening

The present invention relates to a driving circuit of a liquid crystal display, and more particularly to a display driving chip that can avoid flickering in the early stage of wake-up.

Please refer to Fig. 1, which shows a block diagram of a conventional display driver circuit. As shown in Fig. 1, the display driver circuit includes a power management chip 10 and a driver chip 20 to drive a liquid crystal display panel 30 to provide a display screen for an information processing device, such as a smart phone.

The power management chip 10 provides a digital supply voltage V _CC , a positive analog voltage V _SP and a negative analog voltage V _SN to pins A, B and C of the driver chip 20 so that the output channel of the driver chip 20 can generate a source voltage according to display data to drive the pixels of the liquid crystal display panel 30 .

Please refer to Figures 2a and 2b, which respectively illustrate a positive source voltage output circuit and a negative source voltage output circuit in an output channel of a driver chip 20, wherein the positive source voltage output circuit includes an inverting amplifier composed of a PMOS transistor 21 and an NMOS transistor 22, and the negative source voltage output circuit includes an inverting amplifier composed of a PMOS transistor 23 and an NMOS transistor 24. When the output channel needs to output a positive source voltage, the positive source voltage output circuit generates a positive output voltage V _OUTP according to the analog voltage V _X ; when the output channel needs to output a negative source voltage, the negative source voltage output circuit generates a negative output voltage V _OUTN according to the analog voltage V _X.

In addition, generally speaking, when the information processing device is in a sleep state, the power management chip 10 turns off the positive analog voltage V _SP and the negative analog voltage V _SN and only provides the digital supply voltage V _CC to save power consumption.

However, when the power management chip turns off the positive analog voltage V _SP and the negative analog voltage V _SN , the potentials of the pins B and C will be in an uncertain state and may affect the positive output voltage V _OUTP and the negative output voltage V _OUTN respectively through the parasitic diode of the PMOS transistor 21 and the parasitic diode of the NMOS transistor 24, so that the liquid crystal molecules of the liquid crystal display panel 30 are subjected to the DC residual effect, causing the screen of the information processing device to flicker when it is awakened from the sleep state and the liquid crystal display panel 30 is lit again.

In order to solve the above problems, a novel display driver circuit architecture is urgently needed in the art.

One purpose of the present invention is to provide a display driver chip for driving a liquid crystal display panel, which can short-circuit the positive and negative supply voltage input pins to a reference ground when detecting that the two pins are in a floating state, so as to ensure that the output voltages of multiple output channels can be stabilized at the potential of the reference ground during the period when the two pins are in a floating state to avoid the liquid crystal molecules of the liquid crystal display panel from being subjected to a DC residual effect, so that when the two pins regain their respective supply voltages and each output channel recovers the output source voltage, the screen of the liquid crystal display panel will not flicker.

Another object of the present invention is to provide a liquid crystal display that can prevent the screen from flickering when awakened from a sleep state by using the aforementioned display driver chip.

Another object of the present invention is to provide an information processing device which can prevent the screen from flickering when awakened from a sleep state by using the aforementioned liquid crystal display.

To achieve the above-mentioned purpose, a display driver chip that can avoid flickering in the early stage of wake-up is proposed to drive a liquid crystal display panel, and it has: A first floating detection circuit and a first switch, the first floating detection circuit is powered by a digital supply voltage to detect a first input state of a positive analog voltage input terminal, the first switch has a first control terminal and a first channel, the first control terminal is coupled to the output terminal of the first floating detection circuit, the first channel is coupled between the positive analog voltage input terminal and a reference ground, when the first input state is floating, the first floating detection circuit is in an active state to turn on the first channel, and when the first input state is a positive analog voltage, the first floating detection circuit is in an inactive state to disconnect the first channel; and A second floating detection circuit and a second switch, the second floating detection circuit is powered by the digital supply voltage to detect a second input state of a negative analog voltage input terminal, the second switch has a second control terminal and a second channel, the second control terminal is coupled to the output terminal of the second floating detection circuit, the second channel is coupled between the negative analog voltage input terminal and the reference ground, when the second input state is floating, the second floating detection circuit is in an active state to turn on the second channel, and when the second input state is a negative analog voltage, the second floating detection circuit is in an inactive state to disconnect the second channel.

In one embodiment, the first floating detection circuit and the second floating detection circuit are each an inverting logic circuit.

In possible embodiments, the first switch may be an NMOS transistor, a PMOS transistor or a CMOS transistor.

In possible embodiments, the second switch may be an NMOS transistor, a PMOS transistor or a CMOS transistor.

To achieve the above-mentioned purpose, the present invention further proposes a liquid crystal display having a liquid crystal display panel and a driving chip for driving the liquid crystal display panel, and the driving chip has the following characteristics: A first floating detection circuit and a first switch, the first floating detection circuit is powered by a digital supply voltage to detect a first input state of a positive analog voltage input terminal, the first switch has a first control terminal and a first channel, the first control terminal is coupled to the output terminal of the first floating detection circuit, the first channel is coupled between the positive analog voltage input terminal and a reference ground, when the first input state is floating, the first floating detection circuit is in an active state to turn on the first channel, and when the first input state is a positive analog voltage, the first floating detection circuit is in an inactive state to disconnect the first channel; and A second floating detection circuit and a second switch, the second floating detection circuit is powered by the digital supply voltage to detect a second input state of a negative analog voltage input terminal, the second switch has a second control terminal and a second channel, the second control terminal is coupled to the output terminal of the second floating detection circuit, the second channel is coupled between the negative analog voltage input terminal and the reference ground, when the second input state is floating, the second floating detection circuit is in an active state to turn on the second channel, and when the second input state is a negative analog voltage, the second floating detection circuit is in an inactive state to disconnect the second channel.

In one embodiment, the first floating detection circuit and the second floating detection circuit are each an inverting logic circuit.

In possible embodiments, the first switch may be an NMOS transistor, a PMOS transistor or a CMOS transistor.

In possible embodiments, the second switch may be an NMOS transistor, a PMOS transistor or a CMOS transistor.

To achieve the above-mentioned object, the present invention further proposes an information processing device, which has a central processing unit and a liquid crystal display as mentioned above, wherein the central processing unit is used to communicate with the liquid crystal display.

In possible embodiments, the information processing device may be a personal computer, a portable computer, a car computer or a smart phone.

In order to enable the Review Committee to further understand the structure, features, purpose, and advantages of the present invention, the following are attached with drawings and detailed descriptions of preferred specific embodiments.

Please refer to FIG. 3 , which is a block diagram of an embodiment of a liquid crystal display of the present invention. As shown in FIG. 3 , a liquid crystal display 100 includes a driver chip 110 and a liquid crystal display panel 120, wherein the driver chip 110 is coupled to a digital supply voltage V _CC , a positive analog voltage V _SP and a negative analog voltage V _SN via pins A, B and C respectively to drive the liquid crystal display panel 120 under the power supply of these voltage sources, and the driver chip 110 has a first floating detection circuit 111, a first switch 112, a second floating detection circuit 113, a second switch 114 and n output channel circuits 115, where n is an integer greater than 1, wherein the digital supply voltage V _CC , the positive analog voltage V _SP and the negative analog voltage V _SN is provided by a power management chip, and the power management chip will shut down the positive analog voltage V _SP and the negative analog voltage V _SN when in sleep mode, leaving only the digital supply voltage V _CC .

The first floating detection circuit 111 is powered by a digital supply voltage _VCC to detect a first input state of the pin B; the first switch 112 has a first control terminal and a first channel, the first control terminal is coupled to the output terminal of the first floating detection circuit 111, and the first channel is coupled between the pin B and a reference ground GND. When the first input state is floating, a first switch signal SW1 of the first floating detection circuit 111 will be in an active state to turn on the first channel, and when the first input state is a positive analog voltage _VSP , the first switch signal SW1 of the first floating detection circuit 111 will be in an inactive state to disconnect the first channel.

The second floating detection circuit 113 is powered by the digital supply voltage V _CC to detect a second input state of the pin C; the second switch 114 has a second control terminal and a second channel, the second control terminal is coupled to the output terminal of the second floating detection circuit 113, and the second channel is coupled between the pin C and the reference ground GND. When the second input state is floating, a second switch signal SW2 of the second floating detection circuit 113 will be in an active state to turn on the second channel, and when the second input state is a negative analog voltage V _SN , the second switch signal SW2 of the second floating detection circuit 113 will be in an inactive state to disconnect the second channel.

Each output channel circuit 115 generates a source voltage V _OUT (j) according to an analog voltage V _D (j) under the supply of a positive analog voltage V _SP and a negative analog voltage V _SN , where n is an integer greater than 1, and j is an integer between 1 and n. In detail, the output channel circuit 115 has two inverting amplifiers and a multiplexer, the two inverting amplifiers are respectively supplied by the positive analog voltage V _SP and the negative analog voltage V _SN , and the multiplexer is used to select a positive source voltage or a negative source voltage as the source voltage V _OUT (j). To prevent the liquid crystal display panel 120 from generating a DC residual effect, the output channel circuit 115 causes the multiplexer to alternately select the positive source voltage and the negative source voltage as the source voltage V _OUT (j).

In addition, the first switch 112 may be an NMOS transistor, a PMOS transistor or a CMOS transistor, and the second switch 114 may be an NMOS transistor, a PMOS transistor or a CMOS transistor.

In addition, the first floating detection circuit 111 and the second floating detection circuit 113 can each be implemented by an inverting logic circuit. Please refer to FIG. 4a and FIG. 4b, where FIG. 4a shows a circuit diagram of an embodiment of the first floating detection circuit 111; FIG. 4b shows a circuit diagram of an embodiment of the second floating detection circuit 113.

As shown in FIG. 4a, the first floating detection circuit 111 has an NMOS transistor 111a, a resistor 111b and two inverters 111c and 111d, wherein the NMOS transistor 111a and the resistor 111b form an inverter circuit to turn on or off the NMOS transistor 111a according to the potential difference between the pin B and the reference ground GND.

When the pin B is at the positive analog voltage V _SP , the NMOS transistor 111 a is turned on, and the potential of its drain is pulled down to the reference ground GND, so that the first switch signal SW1 is in an inactive state to disconnect the channel of an NMOS transistor 112 a of the first switch 112 . When pin B is floating, the NMOS transistor 111a is not turned on, and the potential of its drain is pulled up to the positive analog voltage V _SP , causing the first switch signal SW1 to be in an active state to turn on the channel of the NMOS transistor 112a, thereby pulling the potential of pin B down to the reference ground GND; and after the potential of pin B is pulled down to the reference ground GND, the gate and source potentials of the NMOS transistor 111a are both the reference ground GND, thereby ensuring that the first switch signal SW1 continues to be in an active state.

As shown in FIG. 4b, the second floating detection circuit 113 has an NMOS transistor 113a and a resistor 113b, wherein the NMOS transistor 113a and the resistor 113b form an inverting circuit to turn on or off the NMOS transistor 113a according to the potential difference between the reference ground GND and the pin C.

When the pin C is at the negative analog voltage V _SN , the NMOS transistor 113 a is turned on, and the potential of its drain is pulled down to the negative analog voltage V _SN , so that the second switch signal SW2 is in an inactive state to disconnect the channel of an NMOS transistor 114 a of the second switch 114 . When pin C is floating, the NMOS transistor 113a is not turned on, and the potential of its drain is pulled up to the positive analog voltage V _SP , causing the second switch signal SW2 to be in an active state to turn on the channel of the NMOS transistor 114a, thereby making the potential of pin C equal to the reference ground GND; and after the potential of pin C is equal to the reference ground GND, the gate and source potentials of the NMOS transistor 113a will be the reference ground GND, thereby ensuring that the first switch signal SW1 continues to be in an active state.

In addition, to reduce static power consumption, the resistor 111b and the resistor 113b may have a larger resistance.

In addition, according to the above description, the present invention further proposes an information processing device. Please refer to FIG. 5, which shows a block diagram of an embodiment of the information processing device of the present invention. As shown in FIG. 5, an information processing device 200 has a central processing unit 210 and a liquid crystal display 220, wherein the central processing unit 210 is used to communicate with the liquid crystal display 220 to instruct the liquid crystal display 220 to enter a sleep state or resume a normal working mode, and the liquid crystal display 220 is implemented by the liquid crystal display 100. In addition, the information processing device 200 can be a personal computer, a portable computer, a car computer or a smart phone.

According to the above design, the present invention has the following advantages: (1) The display driver chip of the present invention can short-circuit the positive and negative supply voltage input pins to a reference ground when detecting that the two pins are in a floating state, so as to ensure that the output voltages of multiple output channels can be stabilized at the potential of the reference ground during the period when the two pins are in a floating state to avoid the liquid crystal molecules of a liquid crystal display panel from being subjected to the DC residual effect, so that when the two pins regain their respective supply voltages and each output channel restores the output source voltage, the screen of the liquid crystal display panel will not flicker; (2) The liquid crystal display of the present invention can prevent the screen from flickering when it is awakened from a sleep state by means of the aforementioned display driver chip; and (3) The information processing device of the present invention can prevent the screen from flickering when it is awakened from a sleep state by means of the aforementioned liquid crystal display.

The invention disclosed in this case is a preferred embodiment. Any partial changes or modifications that are derived from the technical concept of this case and are easily inferred by people familiar with the art do not deviate from the scope of the patent rights of this case.

In summary, this case shows that it is very different from the known technology in terms of purpose, means and effect, and it is the first invention that is practical and indeed meets the patent requirements for invention. We sincerely request the review committee to examine this carefully and grant a patent as soon as possible to benefit the society. This is our utmost prayer.

10: Power management chip

20: Driver chip

21: PMOS transistor

22:NMOS transistor

23: PMOS transistor

24:NMOS transistor

30: LCD panel

100: LCD display

110:Drive chip

111: First floating detection circuit

111a: NMOS transistor

111b:Resistance

111c: Inverter

111d: Inverter

112: First switch

112a: NMOS transistor

113: Second floating detection circuit

113a:NMOS transistor

113b:Resistance

114: Second switch

114a: NMOS transistor

115: Output channel circuit

120: LCD panel

200: Information processing device

210: Central Processing Unit

220: LCD display

FIG. 1 shows a block diagram of an existing display driver circuit; FIG. 2a and FIG. 2b show a positive source voltage output circuit and a negative source voltage output circuit in an output channel of a driver chip of the display driver circuit of FIG. 1, respectively; FIG. 3 shows a block diagram of an embodiment of a liquid crystal display of the present invention; FIG. 4a shows a circuit diagram of an embodiment of a first floating detection circuit of a driver chip of the liquid crystal display of FIG. 3; FIG. 4b shows a circuit diagram of an embodiment of a second floating detection circuit of a driver chip of the liquid crystal display of FIG. 3; and FIG. 5 shows a block diagram of an embodiment of an information processing device of the present invention.

100: LCD display

110:Drive chip

111: First floating detection circuit

112: First switch

113: Second floating detection circuit

114: Second switch

115: Output channel circuit

120: LCD panel

Claims (10)

A display driver chip capable of avoiding flickering in the early stage of wake-up is used to drive a liquid crystal display panel. The chip comprises: a first floating detection circuit and a first switch. The first floating detection circuit is powered by a digital supply voltage to detect a first input state of a positive analog voltage input terminal. The first switch has a first control terminal and a first channel. The first control terminal is coupled to the output terminal of the first floating detection circuit. The first channel is coupled between the positive analog voltage input terminal and a reference ground. When the first input state is floating, the first floating detection circuit is in an active state to turn on the first channel. When the first input state is a positive analog voltage, the first floating detection circuit is in an active state to turn on the first channel. The circuit is in an inactive state to disconnect the first channel; and a second floating detection circuit and a second switch, the second floating detection circuit is powered by the digital supply voltage to detect a second input state of a negative analog voltage input terminal, the second switch has a second control terminal and a second channel, the second control terminal is coupled to the output terminal of the second floating detection circuit, the second channel is coupled between the negative analog voltage input terminal and the reference ground, when the second input state is floating, the second floating detection circuit is in an active state to conduct the second channel, and when the second input state is a negative analog voltage, the second floating detection circuit is in an inactive state to disconnect the second channel. A display driver chip capable of avoiding flickering in the early stage of wake-up as described in claim 1, wherein the first floating detection circuit and the second floating detection circuit are each an inverting logic circuit. A display driver chip capable of avoiding flickering in the early stage of wake-up as described in claim 1, wherein the first switch is a switch selected from a group consisting of an NMOS transistor, a PMOS transistor and a CMOS transistor. A display driver chip capable of avoiding flickering in the early stage of wake-up as described in claim 1, wherein the second switch is a switch selected from a group consisting of an NMOS transistor, a PMOS transistor and a CMOS transistor. A liquid crystal display having a liquid crystal display panel and a driver chip for driving the liquid crystal display panel, wherein the driver chip has: a first floating detection circuit and a first switch, wherein the first floating detection circuit is powered by a digital supply voltage to detect a first input state of a positive analog voltage input terminal, wherein the first switch has a first control terminal and a first channel, wherein the first control terminal is coupled to the output terminal of the first floating detection circuit, wherein the first channel is coupled between the positive analog voltage input terminal and a reference ground, wherein when the first input state is floating, the first floating detection circuit is in an active state to conduct the first channel, and when the first input state is a positive analog voltage, the first control terminal is in an active state to conduct the first channel. A floating detection circuit presents an inactive state to disconnect the first channel; and a second floating detection circuit and a second switch, the second floating detection circuit is powered by the digital supply voltage to detect a second input state of a negative analog voltage input terminal, the second switch has a second control terminal and a second channel, the second control terminal is coupled to the output terminal of the second floating detection circuit, the second channel is coupled between the negative analog voltage input terminal and the reference ground, when the second input state is floating, the second floating detection circuit presents an active state to conduct the second channel, and when the second input state is a negative analog voltage, the second floating detection circuit presents an inactive state to disconnect the second channel. A liquid crystal display as described in claim 5, wherein the first floating detection circuit and the second floating detection circuit are each an inverting logic circuit. A liquid crystal display as described in claim 5, wherein the first switch is a switch selected from a group consisting of an NMOS transistor, a PMOS transistor and a CMOS transistor. A liquid crystal display as described in claim 5, wherein the second switch is a switch selected from a group consisting of an NMOS transistor, a PMOS transistor and a CMOS transistor. An information processing device having a central processing unit and a liquid crystal display as described in any one of claims 5 to 8, wherein the central processing unit is used to communicate with the liquid crystal display. The information processing device as described in claim 9 is a device selected from the group consisting of a personal computer, a portable computer, a car computer and a smart phone.

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