CN1246818C - A current mode data line driving circuit - Google Patents

Abstract

The invention provides a current type data line driving circuit of a display, which comprises an input device, a signal processing unit and an output device. The input device is used for inputting a digital voltage signal and transmitting the digital voltage signal to the signal processing unit, and at the moment, the signal processing unit converts the received digital voltage signal into an analog current signal and outputs the analog current signal to the output device so as to drive at least one data line of the display.

Description

A current mode data line driving circuit

Technical field

The invention provides a data line driving circuit of a display, in particular to a current type data line driving circuit of an organic light-emitting diode (OLED) display.

Background technique

Organic light-emitting diode itself is a current-driven element, and its luminous brightness is determined by the magnitude of the passing current. Currently, OLEDs are applied to matrix displays by controlling the magnitude of the OLED driving current to display different brightnesses (also called the gray value).

According to the differences in driving methods, matrix displays can be divided into passive matrix (passive matrix) displays and active matrix (active matrix) displays. Passive matrix displays use the method of sequentially driving scan lines to drive pixels located in different rows/columns one by one, so the light-emitting time of pixels on each row/column will be limited by the scan frequency and the number of scan lines of the display, which is less It is suitable for displays with large screen and high definition (meaning increased scan lines). An active matrix display forms an independent pixel circuit in each pixel, including a capacitor (Cs), an OLED light-emitting element, and at least two thin-film transistors (TFT), so as to use the pixel circuit to adjust the size of the driving current of the OLED , so even under the requirements of large screen and high definition, it can still provide a stable driving current for each pixel and improve the brightness uniformity of the display.

Please refer to FIG. 1 , which is a basic structure diagram of a known active matrix OLED display panel. As shown in FIG. 1, a display panel 10 includes a matrix composed of multiple columns of data lines (such as DL1, DL2 and DL3) and multiple rows of scanning lines (such as SL1 and SL2), and a plurality of TFTs, Cs and Pixel circuits 11 composed of OLED and other electronic components (not shown) are respectively arranged at intersections of each data line and each scan line. The data lines DL1, DL2 and DL3 are connected to an external data line driving circuit 20 to receive an image data signal, and the scanning lines SL1 and SL2 are connected to an external scanning line driving circuit 30 to receive a switching/addressing signal .

Please refer to FIG. 2 , which is a functional block diagram of the data line driving circuit 20 shown in FIG. 1 . As shown in Figure 2, known data line drive circuit 20 comprises a signal input device 21, is used for inputting a digital voltage signal; digital voltage signal; a shift register circuit (shiftregister) 22, used to control the operation of the data register circuit 23; a data latch circuit (latch circuit) 24, used to store the A digital voltage signal output by 23; a digital to analog converter (digital to analog converter, DAC) 25, used to receive the digital voltage signal output by the data latch circuit 24, and convert the digital voltage signal into an analog voltage signal ; a buffer driver (buffer driver) 26, used to increase the analog voltage signal strength output by the digital-to-analog converter 25; and a signal output device 27, used to receive the enhanced analog voltage signal output by the buffer driver 26, and make the The enhanced analog voltage signal is output to at least one data line of the display panel 10 .

Since the current active matrix OLED display panels mostly use a low-temperature polysilicon (LTPS) manufacturing process to manufacture TFT and other driving elements in the pixel circuit, and the TFT threshold voltage (threshold voltage) produced by the LTPS manufacturing process The phenomenon of drift will occur with the variation of the manufacturing process. Therefore, each pixel in the known OLED display panel cannot generate a fixed output current corresponding to the constant voltage signal transmitted by the external data line driving circuit, thereby affecting the brightness uniformity of the OLED. Especially with the manufacture of large-sized panels, the poor brightness uniformity of pixels on the display panel may cause a difference between the grayscale value of the entire display panel and the grayscale value sent by the driving circuit, and even cause image distortion.

Contents of the invention

Therefore, the object of the present invention is to provide a current mode data line driving circuit of a display to precisely control the grayscale of the display panel.

Another object of the present invention is to provide a circuit structure combining a current mode data line driving circuit and a pixel circuit with threshold voltage shift compensation function, so as to effectively eliminate the uneven brightness of the display panel caused by the threshold voltage shift.

In a preferred embodiment of the present invention, the data line driving circuit includes an input device for inputting a digital voltage signal; a signal processing unit for receiving the digital voltage signal output by the input device and making the digital The voltage signal is converted into an analog current signal; and an output device is used to receive the analog current signal output by the signal processing unit and output the analog current signal to at least one data line of the display. The signal processing unit includes a shift register circuit for controlling the operation of the signal processing unit; a data register circuit for storing the digital voltage signal output by the input device; a data latch circuit , for storing the digital voltage signal output by the data temporary register circuit; a digital-to-analog converter for receiving the digital voltage signal output by the data latch circuit, and converting the digital voltage signal into a an analog voltage signal; a voltage-to-current converter (voltage to current converter), used to receive the analog voltage signal output by the digital-to-analog converter, and convert the analog voltage signal into the analog current signal; and a buffer driver, It is used to increase the intensity of the analog current signal, and output the enhanced analog current signal to the output device.

Since the data line driving circuit of the present invention uses an analog current signal to drive the data line of the display, the size of the driving current of the pixel circuit can be effectively controlled by controlling the magnitude of the analog current signal output by the data line driving circuit, so that the gray value of the display panel It is the same as the gray value sent by the data line driving circuit, thereby avoiding problems such as image distortion.

Description of drawings

FIG. 1 is a basic structural diagram of a known active matrix OLED display panel.

FIG. 2 is a functional block diagram of a conventional data line driving circuit.

FIG. 3 is a functional block diagram of a data line driving circuit of the present invention.

FIG. 4 is a circuit diagram of a voltage-to-current converter of the present invention.

FIG. 5 is a diagram showing the relationship between input voltage and output current of a voltage-to-current converter of the present invention.

FIG. 6 is a circuit diagram of a pixel circuit of the present invention.

Explanation of Symbols in Drawings

10 display panel 11 pixel circuit

20 Data line drive circuit 21 Signal input device

22 shift register circuit 23 data register circuit

24 data latch circuit 25 digital-to-analog converter

26 buffer driver 27 signal output device

30 scan line drive circuit 40 display panel

50 Data line drive circuit 51 Signal input device

52 signal processing unit 521 shift register circuit

522 data temporary register circuit 523 data latch circuit

524 digital-to-analog converter 525 voltage-to-current converter

526 buffer driver 53 signal output device

60 scan line drive circuit Cs capacitor

DL, DL1, DL2 data lines

GNDground

Iout analog current output signal

OLED Organic Light Emitting Diode

SL, 8L1, SL2 scanning lines

Vin analog voltage input signal

M01, M02, M03, M04, M05, M06, M07, M08, M001, M002, M003, M004 Transistors

Vbias, n, Vbias, p, Vdd voltage source

Specific and practical ways

Please refer to FIG. 3 , which is a functional block diagram of a data line driving circuit according to the present invention. As shown in FIG. 3 , a display panel 40 of the present invention utilizes a data line driving circuit 50 and a scanning line driving circuit 60 to control the gray scale of a pixel. The data line driving circuit 50 includes a signal input device 51, which is used to receive image data output by an image display system, usually a digital voltage signal; voltage signal, and convert the digital voltage signal into an analog current signal; and a signal output device 53, which is used to receive the analog current signal output by the signal processing unit 52, and output the analog current signal to the display panel 40 at least one data line.

In a preferred embodiment of the present invention, the signal processing unit 52 includes a shift register circuit 521, a data register circuit 522, a data latch circuit 523, a digital-to-analog converter 524, a voltage current converter 525, and a buffer driver 526. The shift register circuit 521 is used to control the operation of the signal processing unit 52. When the data line driver circuit 50 starts to operate, the shift register circuit 521 controls the access action of the data register circuit 522. The digital image voltage signal transmitted from 51 is stored in the data register circuit 522 . When the data register circuit 522 is full of data, the shift register circuit 521 will dump the signal stored in the data register circuit 522 to the data latch circuit 523 within one operation cycle, so as to The digital-to-analog converter 524 is used for digital/analog signal conversion, and the data register circuit 522 can continue to access external voltage signals at this time. When performing digital/analog signal conversion, the digital-to-analog converter 524 will first convert the digital voltage signal stored in the data latch circuit 523 into an analog voltage signal Vin, and output the analog voltage signal Vin to the voltage current Converter 525 performs voltage/current signal conversion.

Please refer to FIG. 4 and FIG. 5. FIG. 4 is a circuit diagram of the voltage-current converter 525 shown in FIG. 3, and FIG. 5 is an analog voltage input signal Vin and an analog current output signal Iout according to the circuit diagram of the voltage-current converter 525 shown in FIG. relationship diagram between. As shown in FIG. 4, the voltage-to-current converter 525 is composed of a plurality of PMOS transistors (such as M01, M02, M03, and M04, etc.) and NMOS transistors (such as M05, M06, M07, and M08, etc.). (such as Vdd, Vias, p and Vbias, n) and ground GND and other operating conditions, the voltage-to-current converter 525 can convert the analog voltage input signal Vin into an analog current output signal Iout. As shown in FIG. 5, since the analog current output signal Iout generated by the voltage-to-current converter 525 and the analog voltage input signal Vin approximately present a linear relationship in a predetermined operating voltage range (such as 0-8 volts), the present invention can control The magnitude of the analog voltage input signal Vin is converted through the operation of the voltage-to-current converter 525 to obtain an analog current output signal Iout corresponding to an ideal gray value. It is worth noting that the voltage-to-current converter 525 of the present invention can make optimal design changes to the circuit diagram according to the actual operating voltage range and the size of the analog current output signal, and is not limited to the circuit diagram design shown in FIG. 4 .

The analog current output signal converted by the voltage-to-current converter 525 is then sent to the buffer driver 526 to strengthen the anti-spurious signal capability and amplified appropriately, and finally output to the signal output device 53 to drive the pixel circuit of the display panel 40 . Please refer to FIG. 6 , which is a circuit diagram of a pixel circuit of the present invention. The pixel circuit is composed of a data line DL, a scan line SL, a capacitor Cs, a PMOS transistor M003, and three NMOS transistors, including electronic components such as M001, M002, and M004, to provide a stable current to drive an organic light emitting diode. diode OLED. It should be noted that the types of MOS transistors in the pixel circuit, including M001, M002, M003 and M004, can be determined according to the design of the polarity direction of the organic light emitting diode OLED. For example, in other embodiments of the present invention, the MOS transistors M001 , M002 and M004 in the pixel circuit can also be PMOS transistors, and the MOS transistor M003 is an NMOS transistor.

Since transistors M001, M002, M003, and M004 may have threshold voltage shifts in the manufacturing process, in a preferred embodiment of the present invention, transistors M001, M002, M003, and M004 can be achieved through a special connection structure. The threshold voltage compensation function effectively improves the brightness uniformity of the display panel 4O. As shown in FIG. 6, the drain of the NMOS transistor M001 is electrically connected to the data line DL, the gates of the NMOS transistors M001 and M002 and the PMOS transistor M003 are both electrically connected to the scan line SL, and the drain of the PMOS transistor M003 is electrically connected to an external The power supply Vdd, the drain of the NMOS transistor M004 is electrically connected to the source of the NMOS transistor M001, the drain of the NMOS transistor M002 and the source of the PMOS transistor M003, and the source of the NMOS transistor M004 is electrically connected to the organic light emitting diode OLED as Driving transistors for OLEDs. In addition, one end of the capacitor Cs is connected to the source of the NMOS transistor M002 and the gate of the NMOS transistor M004, and the other end of the capacitor Cs is electrically connected to an external power supply Vdd for adjusting the driving current through the OLED.

Wherein when the pixel circuit operates in the on mode, the scanning line SL will receive a high potential signal output from the scanning line driving circuit 60, so that the NMOS transistors M001, M002 and M004 are set in a conducting state, and the PMOS transistor M003 set in an off state. In this open mode, the data line DL also receives the analog current signal Iout output from the data line driving circuit 50, so that the analog current signal Iout sequentially passes through the NMOS transistors M001 and M004, and finally passes through the OLED to the ground electrode GND. Since the NMOS transistor M002 is also in the conduction state at this time, the drain and the gate of the NMOS transistor M004 can be regarded as a short circuit and operate at the junction of a saturation region and a linear region, so that the OLED can obtain a saturation current to stably emit light. .

When the pixel circuit operates in the off mode, the scanning line SL will receive a low potential signal output from the scanning line driving circuit 60, so that the NMOS transistors M001 and M002 are set in an off state, and the PMOS transistor M003 is set in an off state. A conduction state. Since there is a voltage stored in the capacitor Cs in the on mode, the NMOS transistor M004 is still in the on state in the off mode. In the shutdown mode, the drain of the NMOS transistor M004 can be connected to the external power supply Vdd through the turned-on PMOS transistor M003, and the potential provided by the capacitor Cs makes the drain and the gate a short circuit and still maintains At the junction of the saturation region and the linear region, the OLED can continue to obtain a saturation current, so that the gray value of the display panel will not be affected by gate electrode drift.

Compared with the known data line driving circuit which can only provide voltage signals, the data line driving circuit of the present invention uses a voltage-to-current converter to generate a stable analog current signal for driving the data lines of the display. Therefore, by controlling the magnitude of the analog current signal output by the data line driving circuit, the driving current of the pixel circuit can be effectively controlled, so that the gray value of the display panel is the same as the gray value sent by the data line driving circuit, thereby avoiding image distortion, etc. question. In addition, the present invention further provides a pixel circuit with a threshold voltage shift compensation function to be combined with a current-mode data line drive circuit to effectively control the gray scale of the display panel and avoid the known non-uniform brightness caused by the TFT threshold voltage shift of the pixel circuit. And other issues.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and improvements made according to the claims of the present invention shall fall within the protection scope of the present invention.

Claims (11)

1. A current type data line drive circuit, used to drive at least one data line of a display, the data line drive circuit includes: an input device for inputting a digital voltage signal; A signal processing unit is used to receive the digital voltage signal and convert the digital voltage signal into an analog current signal. The signal processing unit includes: a shift register circuit, used to control the operation of the signal processing unit; a data register circuit for storing the digital voltage signal output by the input device; a data latch circuit for storing the digital voltage signal output by the data register circuit; a digital-to-analog converter for receiving the digital voltage signal output by the data latch circuit and converting the digital voltage signal into an analog voltage signal; a voltage-to-current converter for receiving the analog voltage signal output by the digital-to-analog converter and converting the analog voltage signal into an analog current signal; and a buffer driver for increasing the strength of the analog current signal and outputting the enhanced analog current signal to the output device; and An output device is used to output the analog current signal to the data line. 2. The data line driving circuit as claimed in claim 1, wherein the display is an OLED display. 3. The data line driving circuit as claimed in claim 1, wherein the display is an active matrix OLED display. 4. The data line driving circuit as claimed in claim 1, wherein the display is a low temperature polysilicon display. 5. A display, the display includes a plurality of organic light emitting diodes, and a plurality of pixel circuits for driving the organic light emitting diodes, and also includes a current mode data line driving circuit, the driving circuit includes: an input device for inputting a digital voltage signal; A signal processing unit is used to receive the digital voltage signal and convert the digital voltage signal into an analog current signal. The signal processing unit includes: a shift register circuit, used to control the operation of the signal processing unit; a data register circuit for storing the digital voltage signal output by the input device; a data latch circuit for storing the digital voltage signal output by the data register circuit; a digital-to-analog converter for receiving the digital voltage signal output by the data latch circuit and converting the digital voltage signal into an analog voltage signal; a voltage-to-current converter for receiving the analog voltage signal output by the digital-to-analog converter and converting the analog voltage signal into the analog current signal; and a buffer driver for increasing the strength of the analog current signal and outputting the enhanced analog current signal to the output device; and An output device is used to output the analog current signal to the pixel circuit of the display to provide a stable current for the OLED. 6. The display device according to claim 5, wherein each of the pixel circuits comprises: a first transistor, which includes a first gate, a first drain and a first source; a second transistor, which includes a second gate, a second drain and a second source; a third transistor, which includes a third gate, a third drain and a third source; a fourth transistor comprising a fourth gate, a fourth drain and a fourth source, wherein the fourth drain is electrically connected to the first source, the second drain and the third source; a data line electrically connected to the first drain; a scanning line electrically connected to the first gate, the second gate and the third gate; an external power supply electrically connected to the third drain; A storage capacitor includes a first terminal and a second terminal, the first terminal is connected to the external power supply, and the second terminal is connected to the second source and the fourth gate; and An organic light-emitting element includes a third terminal and a fourth terminal, the third terminal is connected to a ground terminal, and the fourth terminal is connected to the fourth source; Wherein when the first voltage is applied to the scanning line, the first gate, the second gate and the fourth gate are set in an on state, and the third gate is set in an off state; and When the second voltage is applied to the scanning line, the first gate and the second gate are set in an off state, and the third gate is set in an open state. 7. The display as claimed in claim 6, wherein the first transistor, the second transistor and the fourth transistor are all NMOS transistors, and the third transistor is a PMOS transistor. 8. The display as claimed in claim 6, wherein the first transistor, the second transistor and the fourth transistor are all PMOS transistors, and the third transistor is an NMOS transistor. 9. The display as claimed in claim 6, wherein the analog current signal is output to the data line. 10. The display as claimed in claim 5, wherein the display is an active matrix OLED display. 11. The display of claim 5, wherein the display is a low temperature polysilicon display.

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