TWI436320B - Source driver - Google Patents

Description

Source driver

This invention relates to a source driver, and more particularly to a source driver for a voltage level of a displacement drive voltage.

In today's information society, electronic display devices are becoming more and more important as information media and various electronic display devices are widely used in industrial devices or household appliances. These electronic display devices are more continuously updated to function for various needs in the information society.

In general, electronic display devices display and transmit various information to users who utilize such information. That is, these electronic display devices convert electronic information signals into optical information signals that are visually identifiable by the user.

In current display devices or systems, such as a Cathode-Ray Tube (CRT) or a Liquid Crystal Display (LCD), the input voltage and the display output are nonlinear, and the input voltage and display are The relationship between the outputs is described by a gamma curve. In the case of a liquid crystal display, the output voltage (ie, gamma voltage) corresponding to each gray scale can be found through the gamma curve. By using these gamma voltages to control the liquid crystal panel to display the correct gray scale, the liquid crystal display can correctly display the image. .

In order to improve the display effect of the liquid crystal display, some liquid crystal panels cut the pixels into two sub-pixels. The two sub-pixels may have different levels of common voltage due to the circuit structure. In this case, when the liquid crystal panel is controlled by the same gamma voltage, the effects of the two sub-pixels may be different, thus affecting the quality of the display. Therefore, the level of the output gamma voltage may be different when different sub-pixels display the same effect. That is to say, when some pixels display the same effect, the gamma voltage after the displacement must be received.

1 is a circuit diagram of a conventional source driver. Referring to FIG. 1, in the source driver 100, the channel buffer 110 is configured to output a displacement voltage ΔV after the displacement of the reference voltage GMAH, wherein the channel buffer 110 is composed of an operational amplifier and a plurality of resistors R. The subtractor is similar. Similarly, the channel buffer 120 shifts the reference voltage GMAL by a displacement voltage ΔV, wherein the channel buffer 120 is composed of an operational amplifier and a plurality of resistors R, the circuit of which is similar to the analog subtractor. After receiving the shifted reference voltages GMAH and GMAL, the resistors AR1 to AR64 divide the voltages to output the shifted gamma voltages AV0 to AV63. The digital analog converter 130 selects one of the output gamma voltages AV0 to AV63 as a driving voltage.

However, the conventional source driver needs to simultaneously shift the reference voltages GMAH and GHAL, that is, the channel buffers 110 and 120 must simultaneously act to synchronously shift the voltage levels of the gamma voltages AV0 to AV63. In addition, since the operational amplifiers of the channel buffers 110 and 120 may be offset, the voltage difference between the output voltage of the channel buffer 110 and the reference voltage GMAH may not be equal to the displacement voltage ΔV, and the output voltage of the channel buffer 120. The voltage difference from the reference voltage and GMAL may not be equal to the displacement voltage ΔV. Thereby, the voltage levels of the gamma voltages AV0 to AV63 may be unevenly shifted.

The invention provides a source driver source driver for shifting the voltage level of a driving voltage.

The present invention provides a source driver including a first resistor string, a first digital analog converter, and a channel buffer. The first series of resistors includes a plurality of resistors in series, each resistor of the first series of resistors providing a corresponding gamma voltage. The first digital analog converter is coupled to the resistors of the first resistor string. The first digital analog converter outputs one of the gamma voltages provided by the resistors as a first output voltage according to a data code. The channel buffer is coupled to the output of the first digital analog converter to shift the voltage level of the first output voltage and output a second output voltage.

In an embodiment of the invention, the channel buffer is displaced by a displacement voltage to a voltage level of the first output voltage.

In an embodiment of the invention, the channel buffer includes an operational amplifier, a first resistor, a second resistor, a third resistor, and a fourth resistor. The operational amplifier outputs a second output voltage. One end of the first resistor receives the displacement voltage, and the other end of the first resistor is coupled to the negative input terminal of the operational amplifier. One end of the second resistor is coupled to the negative input terminal of the operational amplifier, and the other end of the second resistor is coupled to the output terminal of the operational amplifier. One end of the third resistor is coupled to receive the output of the first digital analog converter, and the other end of the third resistor is coupled to the positive input of the operational amplifier. One end of the fourth resistor is coupled to the positive input terminal of the operational amplifier, and the other end of the fourth resistor receives a reference voltage.

In an embodiment of the invention, the resistance values of the first resistor, the second resistor, the third resistor, and the fourth resistor are the same.

In an embodiment of the invention, the source driver further includes a second digital analog converter that outputs a displacement voltage according to a control code.

In an embodiment of the invention, the second digital analog converter comprises a second resistor string and a plurality of switches. The second series of resistors includes a plurality of resistors in series, each resistor of the second series of resistors providing a corresponding partial voltage. The switches select one of the above partial pressures as the displacement voltage according to the control code.

In an embodiment of the invention, the first end of the second resistor string receives the first input voltage, and the second end of the second resistor string receives the second input voltage, wherein the first input voltage is greater than the second input Voltage.

In an embodiment of the present invention, the first end of the first resistor string receives the first reference voltage, and the second end of the first resistor string receives the second reference voltage, wherein the first reference voltage is greater than the second reference Voltage.

In an embodiment of the invention, the source driver further includes a current digital analog converter, wherein the current digital analog converter outputs a displacement current according to a control code. Also, the channel buffer includes an operational amplifier and a resistor. The operational amplifier outputs a second output voltage, wherein the positive input terminal of the operational amplifier is coupled to the output of the first digital analog converter. One end of the resistor is coupled to the negative input terminal of the operational amplifier and receives the displacement current, and the other end of the resistor is coupled to the output end of the operational amplifier and output the second output voltage.

In an embodiment of the invention, the source driver further includes a voltage to current converter, wherein the voltage to current converter converts the reference voltage into a reference current, and the current digital analog current converter outputs a displacement current based on the reference current.

In an embodiment of the invention, the voltage to current converter is a resistor.

In an embodiment of the invention, the second output voltage is less than the first output voltage.

In an embodiment of the invention, the second output voltage is greater than the first output voltage.

Based on the above, the source driver of the embodiment of the present invention can select the magnitude of the displacement voltage according to the control code, and shift the level of the second output voltage according to the displacement voltage to adjust the display effect of the liquid crystal. Moreover, the source driver of the embodiment of the present invention can generate a displacement current according to the control code, and shift the level of the second output voltage according to the displacement current to adjust the display effect of the liquid crystal. Thereby, by shifting the second output voltage, pixels of different common voltage levels can exhibit similar or identical effects.

The above described features and advantages of the present invention will be more apparent from the following description.

First embodiment

2 is a circuit diagram of a source driver in accordance with a first embodiment of the present invention. Referring to FIG. 2 , the source driver 200 includes a first resistor string 210 , a first digital analog converter 220 , a channel buffer 230 , and a second digital analog converter 250 . The first resistor string 210 includes a plurality of resistors R1 R R64 connected in series, and the first terminal A of the first resistor string 210 receives the first reference voltage GMAH, and the second terminal B of the first resistor string 210 receives the second reference The voltage GMAL, wherein the first reference voltage GMAH is greater than the second reference voltage GMAL. The resistors R1 to R64 divide the voltage between the first reference voltage GMAH and the second reference voltage GMAL to provide a plurality of divided voltages as the gamma voltages V0 to V63.

The first digital analog converter 220 is coupled to the resistors R1 R R64 of the first resistor string 210. The first digital analog converter 220 outputs one of the gamma voltages V0 to V63 as the first output voltage V _DAC according to the data code CA, and at this time, the first output voltage V _DAC is not the driving voltage. The channel buffer 230 is coupled to the output 222 of the first digital analog converter 220. The channel buffer 230 includes an operational amplifier 240 and resistors Ra, Rb, Rc, Rd. One end of the first resistor Ra receives the displacement voltage ΔV, and the other end of the first resistor Ra is coupled to the negative input terminal of the operational amplifier 240. One end of the second resistor Rb is coupled to the negative input terminal of the operational amplifier 240, and the other end of the second resistor Rb is coupled to the output terminal of the operational amplifier 240. One end of the third resistor Rc is coupled to receive the output of the first digital analog converter 220, and the other end of the third resistor Rc is coupled to the positive input terminal of the operational amplifier 240. One end of the fourth resistor Rd is coupled to the positive input terminal of the operational amplifier 240, and the other end of the fourth resistor Rd receives the reference voltage V _REF , wherein the reference voltage V _REF can be at the same potential as the ground voltage. It is assumed here that the resistance values of the first resistor Ra, the second resistor Rb, the third resistor Rc, and the fourth resistor Rd are all the same. Accordingly, the circuit in which the operational amplifier OP1 is combined with the resistors Ra, Rb, Rc, and Rd can be regarded as an analog subtractor, and the second output voltage V _OUT outputted by the operational amplifier 240 is equal to the first output voltage V _DAC minus one Displacement voltage ΔV.

In other words, the channel buffer 230 shifts the voltage level of the first output voltage V _DAC by one displacement voltage ΔV and outputs it as the second output voltage V _OUT . The second output voltage V _OUT is output as a driving voltage to drive the liquid crystal display to correspond to the brightness of the gray scale. Thereby, when the voltage levels of the common voltages of different pixels (or sub-pixels) are different, the voltage level of the second output voltage V _OUT can be adjusted according to the displacement voltage ΔV, so that different pixels are in the same gray scale. The brightness of the display is close to or even the same.

In addition, since the displacement reference point of the gamma voltage can refer to a higher common voltage or a lower common voltage of the two pixels, the displacement voltage ΔV can be correspondingly a negative voltage or a positive voltage. When the displacement voltage ΔV is a negative voltage, the second output voltage V _OUT is greater than the first output voltage V _DAC . When the displacement voltage ΔV is a positive voltage, the second output voltage V _OUT will be smaller than the first output voltage V _DAC .

In the present embodiment, the displacement voltage ΔV is provided by the second digital analog converter 250, but may be provided by an external circuit in other embodiments, and is not limited thereto. For example, in an embodiment of the invention, the displacement voltage ΔV is an analog voltage and is dynamically generated by a timing controller (TCON) of the display, wherein the display includes a first resistor string 210, a first digital analog conversion The unit 220 and the channel buffer 230.

In the present embodiment, the second digital analog converter 250 includes a second resistor string 252 and switches SW ₁ SWSW _N , where N is a positive integer. The second resistor string 252 includes a plurality of resistors RV_1 R RV_N connected in series, and the first terminal C of the second resistor string 252 receives the first input voltage ΔV _{REF — H} , and the second terminal D of the second resistor string 252 receives the second The input voltage ΔV _{REF_L} , wherein the first input voltage ΔV _{REF — H is} greater than the second input voltage ΔV _{REF — L} .

The resistors RV_1 to RV_N divide the voltage between the first input voltage ΔV _{REF_H} and the second input voltage ΔV _{REF_L} to provide a plurality of divided voltages ΔV ₁ to ΔV _N . The switches SW ₁ to SW _N receive the divided voltages ΔV ₁ to ΔV _N , respectively, and select one of the divided voltages ΔV ₁ to ΔV _N as the displacement voltage ΔV according to the control code CB. Accordingly, the second digital analog converter 250 outputs the displacement voltage ΔV according to the control code CB, wherein the number of bits of the control code CB can be the same as the number of the switches SW ₁ to SW _N to be separately controlled by the bits of the control code CB. Switch SW ₁ ~SW _N .

In addition, FIG. 2 shows a 6-bit source driver, that is, the resistance of the first resistor string 210 is 2 ⁶ , and if it is to be changed to an 8-bit source driver, the first resistor string is added. The number of resistors connected in series in 210 is 256 (that is, the 8th power of 2). Accordingly, the source drivers of other bit numbers (for example, 10 bits) are analogous.

Second embodiment

3 is a circuit diagram of a source driver in accordance with a second embodiment of the present invention. Please refer to FIG. 2 and FIG. 3, which differ in the channel buffer 330, the current digital analog converter 350 and the voltage to current converter 360. The channel buffer 330 shifts the first output voltage V _DAC according to a displacement current ΔI. The channel buffer 330 includes an operational amplifier 240 and a resistor Re. One end of the resistor Re is coupled to the negative input terminal of the operational amplifier 240 and receives the displacement current ΔI. The other end of the resistor Re is coupled to the output terminal of the operational amplifier 240 and outputs a second output voltage V _OUT . The positive input terminal of the operational amplifier 240 is coupled to the output 222 of the first digital analog converter 220 to receive the first output voltage V _DAC .

According to the circuit principle of the operational amplifier, the potential of the negative input terminal of the operational amplifier 240 is equal to the voltage of its positive input terminal, that is, the potential of the negative input terminal of the operational amplifier 240 is approximately equal to the first output voltage V _DAC , and the displacement current ΔI flows. The voltage drop is generated by the resistor Re such that the second output voltage V _OUT output by the operational amplifier 240 is equal to the product of the first output voltage V _DAC minus the displacement current ΔI and the resistance of the resistor Re (ie, V _DAC ─ ΔI × Re ). Accordingly, when the displacement current ΔI is changed, the voltage level of the second output voltage V _OUT also changes.

In the present embodiment, the displacement current ΔI is provided by the current digital analog converter 350, and other embodiments may be provided by an external circuit, and are not limited thereto. The current-type digital analog converter 350 converts the reference current I _REF into a displacement current ΔI according to the control code CB, and outputs the displacement current ΔI to the channel buffer 330, wherein the control code CB in this embodiment may be the same or different from the above embodiment. Said. Moreover, in the present embodiment, the reference current I _REF is provided by the voltage-to-current converter 360. In other embodiments, the reference current I _REF may also be provided by an external circuit, and is not limited thereto. The voltage to current converter 360 converts the reference voltage V _REF into a reference current I _REF , wherein the voltage to current converter 360 can be a resistor.

In summary, the source driver of the embodiment of the present invention can select the magnitude of the displacement voltage according to the control code, and shift the voltage level of the second output voltage according to the displacement voltage to adjust the display effect of the liquid crystal. Moreover, the source driver of the embodiment of the present invention can generate a displacement current according to the control code, and shift the voltage level of the second output voltage according to the displacement current to adjust the display effect of the liquid crystal. Thereby, by shifting the second output voltage, pixels of different common voltage levels can exhibit similar or identical effects. In addition, the channel buffer can be used to drive the voltage level of the voltage to simplify the circuit design complexity. Moreover, the gamma voltage is shifted by an appropriate voltage displacement during the scanning of the corresponding display, thereby avoiding the corsstalk phenomenon of the display. In addition, since the gamma voltage is shifted by the single operational amplifier 240, the offset of the operational amplifiers of the channel buffers 230 and 330 is eliminated.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100, 200, 300. . . Source driver

110, 120, 230. . . Channel buffer

130. . . Digital analog converter

210. . . First resistor string

220. . . First digital analog converter

222, A, B, C, D. . . End point

240. . . Operational Amplifier

250. . . Second digital analog converter

252. . . Second resistor string

350. . . Current digital analog converter

360. . . Voltage to current converter

AR1~AR64, R, R1~R64, Ra~Re, RV_1~RV_N. . . resistance

AV0~AV63, V0~V63. . . Gamma voltage

ΔV. . . Displacement voltage

ΔI. . . Displacement current

GMAH, GMAL, V _REF . . . Reference voltage

I _REF . . . Reference current

V _DAC , V _OUT . . . The output voltage

ΔV _{REF_H} , ΔV _{REF_L} . . . Input voltage

ΔV ₁ ~ ΔV _N . . . Partial pressure

CA. . . Data code

CB. . . Control code

SW ₁ ~SW _N . . . switch

1 is a circuit diagram of a conventional source driver.

2 is a circuit diagram of a source driver in accordance with a first embodiment of the present invention.

3 is a circuit diagram of a source driver in accordance with a second embodiment of the present invention.

200. . . Source driver

230. . . Channel buffer

210. . . First resistor string

220. . . First digital analog converter

222, A, B, C, D. . . End point

240. . . Operational Amplifier

250. . . Second digital analog converter

252. . . Second resistor string

R1~R64, Ra~Rd, RV_1~RV_N. . . resistance

V0~V63. . . Gamma voltage

ΔV. . . Displacement voltage

GMAH, GMAL, V _REF . . . Reference voltage

V _DAC , V _OUT . . . The output voltage

ΔV _{REF_H} , ΔV _{REF_L} . . . Input voltage

ΔV ₁ ~ ΔV _N . . . Partial pressure

CA. . . Data code

CB. . . Control code

SW ₁ ~SW _N . . . switch

Claims (6)

A source driver includes: a first resistor string comprising a plurality of resistors connected in series, each of the resistors of the first resistor string providing a corresponding gamma voltage; a first digital analog converter, coupled Connecting the resistors of the first resistor string, wherein the first digital analog converter outputs one of the gamma voltages provided by the resistors as a first output voltage according to a data code; a channel buffer And an output of the first digital analog converter, the voltage level of the first output voltage is shifted by a displacement voltage to output a second output voltage; and a current digital analog converter is controlled according to a control The code output a displacement current, wherein the channel buffer comprises: an operational amplifier outputting the second output voltage, wherein a positive input terminal of the operational amplifier is coupled to an output end of the first digital analog converter; and a resistor, wherein One end of the resistor is coupled to the negative input end of the operational amplifier and receives the displacement current, and the other end of the resistor is coupled to the output end of the operational amplifier and outputs the second input Voltage. The source driver of claim 1, wherein a first end of the first resistor string receives a first reference voltage, and a second end of the first resistor string receives a second reference voltage And the first reference voltage is greater than the second reference voltage. The source driver according to claim 1, further comprising a voltage to current converter, wherein the voltage to current converter converts a reference voltage into a reference current, and the current digital analog current converter is based on The reference current outputs the displacement current. The source driver of claim 3, wherein the voltage to current converter is a resistor. The source driver of claim 1, wherein the second output voltage is less than the first output voltage. The source driver of claim 1, wherein the second output voltage is greater than the first output voltage.