CN100495128C - A Gamma Reference Voltage Generating Circuit - Google Patents

Abstract

This invention discloses one Gamma reference voltage generation circuit for film transistor LCD, which comprises direct stable voltage, positive gamma reference voltage generation circuit and is characterized by the following: the said reference voltage generate circuit output end is connected with switch and reverse charge pump circuit to form negative Gamma reference generation circuit; according to LCD symmetric voltage to transparence property curve by simple circuit and positive Gamma reference voltage to Gamma reference voltage.

Description

A Gamma Reference Voltage Generating Circuit

technical field

The invention relates to a thin film transistor liquid crystal display (TFT-LCD), in particular to a gamma (GAMMA) reference voltage generating circuit of the thin film transistor liquid crystal display.

Background technique

Liquid crystal display technology is developing very fast, and due to its light weight, liquid crystal display devices are widely used in various display fields.

As an important part of the TFT-LCD module, the gamma reference voltage generation circuit plays a vital role in the gray scale adjustment of the TFT-LCD. The function of the gamma reference voltage generation circuit is to set the gamma reference voltages GMA1, GMA2, etc. according to the required gamma curve, as the reference voltage for the grayscale display of the thin film transistor liquid crystal display. For example, the gamma reference voltages in the positive pressure area are GMA1 to GMA5, the gamma reference voltages in the negative pressure area are GMA6 to GMA10, and a gamma reference voltage is set every 16 gray scales. Each gamma reference voltage is input into the signal driving circuit of the thin film transistor liquid crystal display, and all gray scale voltages are generated through the digital-to-analog converter of the signal driving circuit. Therefore, the grayscale and transmittance curves of the thin film transistor liquid crystal display module fit the required gamma curve.

According to the voltage-transmittance curve of the liquid crystal material, various gamma reference voltage values are obtained through calculation, and then the gamma reference voltage generating circuit is used to generate these gamma reference voltages, which are provided to the signal driving circuit. The existing gamma reference voltage generating circuit is shown in FIG. 1 .

The DC stable voltage VDD provided by the power supply, the secondary voltage divider circuit on the right side of Figure 1 generates each gamma reference voltage through a gamma resistor series R0, R1...R5-1, R5-2...R9, R10, while the left side of Figure 1 The main voltage divider loop and the feedback operational amplifier circuit on the side are voltage stabilizing circuits, which stabilize the voltage values of GMA3, GMA5.5 and GMA8 of the secondary voltage divider circuit.

The main disadvantage of the prior art is that the determination of the gamma resistance value is very cumbersome, and different TFT liquid crystal display panels and different liquid crystal material characteristics need to be adjusted with different gamma resistance values, so a large amount of calculation and debugging work is required , which greatly affects the work efficiency of engineers and technicians. Moreover, each gamma reference voltage value should be input to the pins of the corresponding signal drive circuit, and often in order to improve the grayscale display characteristics, the number of gamma reference voltages will be increased, and the prior art needs to increase the corresponding number of signal drive circuits. Therefore, it is not conducive to the integration of the signal driving circuit, and the display resolution is limited.

Contents of the invention

The purpose of the present invention is to address the defects of the prior art, and the liquid crystal material used in this type of thin film transistor liquid crystal display such as fringe field switching type (FFS) has the characteristics of the symmetrical voltage-transmittance curve as shown in Figure 2, A new gamma reference voltage generation circuit is provided, which greatly reduces the workload of gamma resistance debugging and reduces the number of gamma reference voltage input pins of the signal drive circuit.

In order to achieve the above object, the present invention provides a gamma reference voltage generation circuit, including: a DC stable voltage, a gamma reference voltage generation circuit in the positive pressure region, characterized in that: the output terminal of the gamma reference voltage generation circuit in the positive pressure region A gamma reference voltage generating circuit in the negative pressure region composed of a switch and an inverse charge pump circuit is connected. The switch is a two-state switch controlled by a high-frequency square wave signal. When the square wave is in the first level state, the switch is connected to Gamma reference voltage in the positive pressure region; when the square wave is in the second level state, the switch is grounded; the reverse charge pump circuit is composed of two capacitors and two diodes; wherein one end of the first capacitor is connected to the two The other end is connected to the P pole of the PN junction of the first diode, and at the same time connected to the N pole of the PN junction of the second diode; the N pole of the first diode is connected to the reference voltage; The P pole is connected to one end of the second capacitor; the other end of the second capacitor is connected to the reference voltage. The frequency of the high frequency square wave signal is greater than or equal to 50kHz. The high frequency square wave signal is generated by a clock control device of the drive circuit.

The gamma reference voltage generation circuit of the present invention only needs to adjust the gamma resistance value used to generate the gamma reference voltage in the positive pressure region of the symmetrical voltage-transmittance curve, and the circuit formed by the above-mentioned switch and the reverse charge pump circuit automatically The gamma reference voltage corresponding to the negative pressure area is generated, and the workload of gamma resistor debugging is reduced to half of the workload of the prior art.

In addition, the circuit for generating the gamma reference voltage in the negative pressure region from the gamma reference voltage in the positive pressure region according to the present invention can be built in the signal driving circuit, so that the input terminal of the signal driving circuit only needs to provide the gamma reference voltage in the positive pressure region Only voltage pins are required, so the number of gamma reference voltage input pins of the signal driving circuit is correspondingly reduced.

The gamma reference voltage generating circuit in the present invention is composed of a switch and an inverse charge pump circuit, which is greatly simplified compared with existing similar circuits, which reduces the area and power consumption of the circuit. In addition, because the adopted circuit is simple and does not depend on the parameters of the circuit components, the circuit precision can be improved.

Various advantages of the present invention will be more clearly reflected in specific embodiments.

Description of drawings

Fig. 1 is a previous gamma reference voltage generating circuit;

Figure 2 is a symmetrical voltage-transmittance characteristic curve of a liquid crystal material;

Fig. 3 is the schematic diagram of the gamma reference voltage generation circuit of the present invention;

Fig. 4 is a structural diagram of the circuit part for generating the gamma reference voltage in the negative pressure region by using the gamma reference voltage in the positive pressure region in the gamma reference voltage generating circuit of the present invention;

Fig. 5 is a schematic diagram of signals when the circuit in the embodiment of the present invention is working.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

A liquid crystal material used in a thin film transistor liquid crystal display has a symmetrical voltage-transmittance characteristic curve as shown in FIG. 2 . Each gamma reference voltage value is determined according to the characteristic curve and the required gray scale. If it is determined that the gamma reference voltage values in the positive pressure area are GMA1, GMA2, GMA3, GMA4, and GMA5, then due to the symmetrical voltage-transmittance characteristic curve, the gamma reference voltage values in the negative pressure area GMA6, GMA7, GMA8, GMA9 , GMA10 and the gamma reference voltage values GMA1 , GMA2 , GMA3 , GMA4 , GMA5 in the positive pressure zone are mirror images of each other with respect to the symmetrical center voltage VCNETER of the voltage-transmittance characteristic curve. Right now:

GMA1+GMA10=2VCNETER

GMA2+GMA9=2VCNETER

GMA3+GMA8=2VCNETER

GMA4+GMA7=2VCNETER

GMA5+GMA6=2VCNETER

Therefore, after the gamma reference voltage values in the positive pressure area are determined to be GMA1, GMA2, GMA3, GMA4, and GMA5 in sequence by using the left part of the circuit in FIG. 3, the gamma reference voltage in the negative pressure area on the right side of FIG. Generate corresponding gamma reference voltages GMA6, GMA7, GMA8, GMA9, GMA10 in the negative pressure zone.

The left part of the circuit in Figure 3 uses the DC stable voltage VDD to generate the corresponding gamma reference voltages GMA1 to GMA5 in the positive pressure region through the sub-voltage divider circuit composed of resistor strings R0, R1, R2, R3, R4, and R5. The voltage stabilization function of the main voltage divider circuit and the feedback operational amplifier circuit stabilizes the gamma reference voltages GMA2 and GMA4 in the positive pressure region of the secondary voltage divider circuit. The circuit on the right part of FIG. 3 , that is, the gamma reference voltage generation circuit 101 in the negative pressure region, will be described in detail below.

As shown in Fig. 4, the gamma reference voltage generation circuit in the negative pressure region is composed of two-state switches T1 and T1, and an inverting charge pump circuit.

Wherein, the two-state switches T1 and T1 are controlled by a high frequency square wave signal, the frequency of the high frequency square wave signal is greater than or equal to 50 kHz, and can be conveniently generated by a control device such as a clock controller of the driving circuit. When the high-frequency square wave signal is in the high level state as shown in Figure 5, the switch T1 is turned on, the switch T1 is cut off, and the switch circuit is connected to the Gamma reference voltage in the positive pressure region; when the high-frequency square wave signal is in the In the low state shown in 5, the switch T1 is turned on, the switch T1 is turned off, and the switch circuit is grounded. The reverse charge pump circuit consists of two capacitors and two diodes; one end of the capacitor C1 is connected to the two-state switches T1 and T1, the other end is connected to the P pole of the diode D1, and is connected to the N pole of the diode D2; The N pole of D1 is connected to the reference voltage; the P pole of the diode D2 is connected to one end of the capacitor C2; the other end of the capacitor C2 is connected to the reference voltage. The Gamma reference voltage in the positive pressure zone is input from T1 in the two-state switch, and the corresponding Gamma reference voltage in the negative pressure zone is output from the P pole end of D2 of the inverting charge pump. Among them, the time constant of the reverse charge pump circuit is much larger than the period of the high-frequency square wave signal.

The detailed working principle of using the gamma reference voltage generation circuit 101 in the negative pressure region to obtain the gamma reference voltage in the negative pressure region through the gamma reference voltage in the positive pressure region in this specific embodiment will be further described below in combination with the working principle of the reverse charge pump circuit .

The basic principle of the reverse charge pump is that the bias state of the diode remains reverse biased to maintain the charge on the capacitor. Since the high-frequency square wave signal controls the state of the two-state switches T1 and T1, the potential Va at point a in Figure 4 changes at the same frequency as the high-frequency square wave signal, as shown in Figure 5. When the circuit is in the first half cycle when T1 is closed and T1 is off, the potential at point a is Va=GMA1. Considering that the diode D1 needs to be reverse-biased, C1 can hold the charge, so the potential at point b does not exceed Vb=V1-VD, where V1 is the reference voltage, and VD is the threshold voltage of the diode. Since the charging of C1 utilizes the reverse leakage current of the diode D1, the charging speed is slow, but after going through multiple first half cycles when T1 is closed and T1 is open, the potential at point b can always be charged to V1-VD at the end. After the above charging process is completed, the voltage difference across C1 can reach V1-VD-GMA1 in the first half cycle. At this time, when the circuit enters the second half period when T1 is closed and T1 is disconnected, the potential Va at point a=0, since the time constant of the reverse charge pump circuit is much larger than the period of the high-frequency square wave signal, the voltage difference across C1 is still V1-VD-GMA1, then the potential at point b is pulled down to Vb=V1-VD-GMA1<V1-VD, so the capacitor C1 will continue to charge, and also because the reverse leakage current of the diode D1 is used for charging, charging The speed is slow. In the second half cycle, the voltage difference across C1 only increases by a small amount of ΔV, and the voltage difference across capacitor C1 becomes V1-VD-GMA1+ΔV. In the next first half cycle when T1 is closed and T1 is off, the potential at point a is Va=GMA1, and the potential at point b is Vb=V1-VD+ΔV>V1-VD, so capacitor C1 will discharge, making the potential at point b The potential returns to Vb=V1-VD. If the small fluctuation ΔV of the above-mentioned voltage difference is ignored, the voltage difference between the two ends of the capacitor C1 is basically stable as V1-VD-GMA1, which does not change with time, so the potential of point b follows the potential of point a, with the same high-frequency square wave signal The frequency changes on two levels of Vb=V1-VD and V1-VD-GMA1.

When the potential at point b is Vb=V1-VD-GMA1, also considering that diode D2 needs to be reverse-biased, capacitor C2 can hold the charge, so when the potential at point c is stable, it is pulled to GMA10=V1-2VD-GMA1, and then when b The potential of the point becomes Vb=V1-VD, and the diode is still reverse-biased, so the state of charge on the capacitor C2 remains unchanged, and the potential of point c is still stable at GMA10=V1-2VD-GMA1. In this way, the potential GMA10 at point c is a single level that does not change with time.

If the reference voltage V1=2VCENTER+2VD is set, then GMA10=2VCNETER-GMA1. In this way, the function of generating the gamma reference voltage GMA10 in the negative pressure region from the gamma reference voltage GMA1 in the positive pressure region is realized. The same method can be used to generate corresponding gamma reference voltages in the negative region from other positive region gamma reference voltages, that is, GMA9 is generated from GMA2, GMA8 is generated from GMA3, GMA7 is generated from GMA4, and GMA6 is generated from GMA5.

As shown in Figure 3, in this embodiment, the positive regions GMA1, GMA2, GMA3, GMA4, and GMA5 are obtained by adjusting the gamma resistance values R0 to R5 used to generate the gamma reference voltage in the positive pressure region of the symmetrical voltage-transmittance curve Afterwards, the circuit 101 composed of the above-mentioned switch and the reverse charge pump circuit automatically generates the corresponding gamma reference voltages GMA10, GMA9, GMA8, GMA7, GMA6 in the negative pressure zone. Compared with the prior art, the gamma resistance that needs to be adjusted Quantity cut in half.

Similarly, the circuit described in the present invention can be built into the signal driving circuit, so that the input terminal of the signal driving circuit only needs to provide the gamma reference voltage pin in the positive pressure region, and compared with the prior art, the number of pins is reduced by half . In this embodiment, there are 5 pins, so the number of input pins of the signal driving circuit is correspondingly reduced by 5.

In addition, the gamma reference voltage generating circuit of the present invention is composed of a switch and an inverse charge pump circuit, which is greatly simplified compared with the existing similar circuits, which reduces the area and power consumption of the circuit. In addition, because the adopted circuit is simple and does not depend on the parameters of the circuit components, the precision of the circuit is improved, and the precision of the generated gamma reference voltage is also improved accordingly.

This embodiment is only used to illustrate rather than limit the gamma reference voltage generating circuit of the thin film transistor liquid crystal display driving circuit of the present invention. Unless otherwise indicated, the invention is not limited to the specific details described above. For example, the number of gamma reference voltages can be changed according to the gray level. On the premise of not departing from the essential characteristics of the circuit, the present invention also has other specific embodiments. Any modifications and changes that conform to the characteristics of the present invention are within the scope of the present invention.

Claims (4)

1. A gamma reference voltage generation circuit, comprising: a DC stable voltage, a gamma reference voltage generation circuit in a positive pressure region, characterized in that: the output terminal of the gamma reference voltage generation circuit in a positive pressure region is connected with a switch and an inverter Gamma reference voltage generation circuit in the negative pressure region composed of a charge pump circuit, the switch is a two-state switch controlled by a high frequency square wave signal, when the square wave is in the first level state, the switch is connected to the Gamma in the positive pressure region Reference voltage; when the square wave is in the second level state, the switch is grounded; the reverse charge pump circuit is composed of two capacitors and two diodes; wherein one end of the first capacitor is connected to the two-state switch, and the other end It is connected to the P pole of the PN junction of the first diode and connected to the N pole of the PN junction of the second diode; the N pole of the first diode is connected to the reference voltage; the P pole of the second diode is connected to the second One end of the capacitor is connected; the other end of the second capacitor is connected to the reference voltage. 2. A gamma reference voltage generation circuit according to claim 1, wherein the frequency of the high-frequency square wave signal is greater than or equal to 50 kHz. 3. A gamma reference voltage generation circuit according to claim 1, characterized in that the high-frequency square wave signal is generated by a clock control device of the drive circuit. 4. A gamma reference voltage generating circuit according to claim 1, characterized in that: said reference voltage is the difference between twice the voltage of the liquid crystal material and the symmetrical center voltage of the transmittance curve and twice the diode threshold voltage and.

Images