A pixel driving circuit for a silicon-based OLED micro-display to avoid bright spot defects

Abstract

The application discloses a pixel driving circuit of a silicon-based OLED micro display avoiding bright spot defects, and belongs to the technical field of integrated circuits, and particularly relates to a pixel driving circuit of a silicon-based OLED micro display avoiding bright spot defects and a driving method thereof. The circuit comprises a voltage boosting module and a unit pixel driving circuit; the voltage boosting module is used for programmably boosting a scanning gate voltage according to a control signal; and the unit pixel driving circuit adopts a full NMOS structure. The application provides a pixel driving circuit and a driving method thereof, which can avoid bright spot defects, reduce process sensitivity, and ensure normal brightness and gray scale performance in a unit driving circuit with a limited size.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit technology, specifically relating to a pixel driving circuit and driving method for silicon-based OLED microdisplays that avoids bright spot defects. Background Technology

[0002] Among existing silicon-based OLED pixel structures, the 3T1C (3 transistors + 1 holding capacitor) is a widely used driving architecture. This structure uses switching transistors to write signals, driving transistors to regulate the emission current, and holding capacitors to maintain the grayscale potential. Existing 3T1C unit pixel driving circuit structures typically include a switching structure, a driving structure, and a sample-and-hold structure. The switching structure can employ an NMOS+PMOS transmission transistor structure to achieve pixel data writing and holding.

[0003] In the manufacturing process of silicon-based OLED microdisplays, various defects are inevitably generated due to limitations in current material properties and technological levels. Bright spot defects are one of the most prominent problems. A bright spot defect refers to an abnormally bright pixel that continuously emits light on the display screen. Its characteristic is that its brightness is significantly higher than that of the surrounding normal pixels, and it is usually called a constant bright spot. Alternatively, an abnormally bright spot that continuously emits light under black screen conditions is characterized by emitting light when the screen is black but not when the screen is white, and it is usually called a very bright spot.

[0004] Bright spots are visually disruptive defects, especially against black or dark backgrounds. They become particularly noticeable, severely compromising the integrity and consistency of the image and significantly reducing image quality. In VR / AR applications, when users wear the device, bright spots act like blemishes in the image, diminishing the realism and immersion of the experience and affecting the user's perception and interaction with the virtual scene. The presence of bright spots also reflects product quality and reliability issues; a large number of bright spots can lead to lower yield rates, increased production costs, and a decline in product competitiveness.

[0005] In existing 3T1C structures, an NMOS+PMOS transmission transistor structure is typically used as the switching transistor. The reliability of the PMOS transistor located in the N-well is highly dependent on the isolation structure in the CMOS process. When there are defects in the N-well isolation or process fluctuations, the PMOS is prone to problems such as parasitic drain conduction, substrate potential coupling, threshold drift, and short-circuit leakage, causing the pixel to remain on and thus forming a persistent bright spot defect that is difficult to compensate for.

[0006] The mechanism behind the exceptionally bright pixels is primarily related to the charge retention characteristics during the grayscale retention stage. In the 3T1C structure, pixel brightness is determined by the potential stored in the retention capacitor. When a high-potential region around a pixel experiences abnormal charging and discharging coupling with the retention capacitor due to localized process defects, the stored voltage of the retention capacitor deviates from the set value, causing the pixel to emit abnormal light under black or low-grayscale display conditions.

[0007] Existing compensation circuits typically require additional transistors and wiring resources, increasing pixel area occupancy and making it difficult to reduce pixel size. Furthermore, they struggle to maintain sufficient brightness output at low frame rates. Overall, current technologies still face challenges in suppressing bright spot defects, including high process sensitivity, limited driving capabilities, and complex pixel structures. Summary of the Invention

[0008] This invention proposes a pixel driving circuit and its driving method that avoids bright spot defects, reduces process sensitivity, and ensures normal brightness and grayscale performance in a unit driving circuit with limited size.

[0009] A silicon-based OLED microdisplay pixel driving circuit that avoids bright spot defects is characterized by comprising a boost module and a unit pixel driving circuit.

[0010] The boost module performs programmable boosting of the scanning gate voltage according to the control signal;

[0011] The unit pixel driving circuit adopts an all-NMOS structure.

[0012] Furthermore, the boost module includes input terminals CONTROL and VDD, and output terminal Vsel; this module programmatically boosts the VDD voltage according to the CONTROL signal to generate Vsel.

[0013] By adjusting the CONTROL value, the voltage Vsel of ROW_SEL is adjusted to drive the silicon-based OLED microdisplay's driving circuit to avoid bright spot defects and ensure that grayscale is not lost.

[0014] Furthermore, the unit pixel driving circuit includes input terminals DATA_in and ROW_SEL. Through a switching structure, a driving structure, and a holding structure, the electrical signal is converted into an optical signal by the OLED light-emitting device to achieve self-emission.

[0015] Furthermore, the switching structure is an NMOS transistor T1, the holding structure is a capacitor C, and the driving structure is an NMOS transistor T2, wherein:

[0016] The source is connected to DATA_in, the gate of T1 is connected to the input terminal ROW_SEL, the drain of T1 is connected to capacitor C and the gate of T2, and the substrate is connected to GND.

[0017] One end of capacitor C is connected to the drain of T1 and the gate of T2, and the other end is connected to GND;

[0018] The gate of NMOS transistor T2 is connected to the drain of T1, the source is connected to the anode of the OLED, the cathode of the OLED is connected to the common negative voltage VCOM, the drain of T2 is connected to VDD, and the substrate is connected to GND.

[0019] A driving method for a pixel driving circuit of a silicon-based OLED microdisplay that avoids bright spot defects includes the following steps:

[0020] Step S1: Power on the drive circuit and initialize the circuit configuration;

[0021] Step S2: Adjust the VCOM voltage by modifying the register configuration;

[0022] Step S3: By modifying the data of the built-in test video signal, adjust the display to 255 grayscale and test the corresponding brightness;

[0023] Step S4: By modifying the data of the built-in test video signal, adjust the display to 252 grayscale levels and test the corresponding brightness;

[0024] Step S5: Determine whether there is a significant difference in grayscale display brightness. If there is a significant difference, proceed to step S7; otherwise, proceed to step S6.

[0025] Step S6: By modifying the register configuration, adjust the CONTROL signal, increase the voltage Vsel of ROW_SEL, and continue to step S4;

[0026] Step S7: Adjust the GAMMA curve by modifying the register configuration to improve the display effect;

[0027] Step S8: Complete driver configuration.

[0028] Compared with the prior art, the technical solution of this invention uses NMOS throughout, avoiding the parasitic drain conduction, substrate potential coupling, threshold drift, short-circuit leakage and other N-well process risks introduced by PMOS devices located in N-wells, thus reducing the probability of constant bright spot defects. Secondly, by using an all-NMOS pixel driving circuit, the problem of high grayscale loss and brightness loss that may be caused by the poor high-level transmission capability of NMOS is solved. Thirdly, within the operating voltage range allowed by semiconductor process, a reasonable driving configuration balances grayscale integrity, brightness performance and circuit reliability.

[0029] This invention can avoid bright spot defects, reduce process sensitivity, and ensure normal brightness and grayscale performance within a limited-size unit driving circuit. Compared to schemes that introduce complex compensation structures, the pixel unit structure of this invention is simple, without introducing a large number of additional transistors and wiring resources, which is beneficial for controlling pixel area and process implementation complexity. Furthermore, after configuration using the driving method described in this invention, the display effect is consistent with that of 3T1C, and it has the yield advantage of avoiding bright spot defects. In contrast, driving configurations of silicon-based OLED microdisplay pixel driving circuits that avoid bright spot defects result in the loss of high grayscale information and a deterioration in display effect.

[0030] Instruction manual illustrations

[0031] Figure 1 This is a block diagram of the pixel driving circuit system of the present invention.

[0032] Figure 2 This is a circuit diagram of the pixel driving circuit of the present invention.

[0033] Figure 3 This is a flowchart of the driving method in this invention.

[0034] Figure 4 This is a schematic diagram showing the brightness and grayscale effects before and after the pixel driving circuit configuration of the present invention. Detailed Implementation

[0035] Example 1: A silicon-based OLED microdisplay pixel driving circuit to avoid bright spot defects, including a boost module and a unit pixel driving circuit;

[0036] The boost module performs programmable boosting of the scanning gate voltage according to the control signal;

[0037] The unit pixel driving circuit adopts an all-NMOS structure.

[0038] The all-NMOS structure avoids the use of PMOS devices located in the N-well, structurally reducing the risk of bright spot defects caused by N-well process defects.

[0039] Furthermore, the boost module includes input terminals CONTROL and VDD, and output terminal Vsel; this module programmatically boosts the VDD voltage according to the CONTROL signal to generate Vsel.

[0040] By adjusting the CONTROL value, the voltage Vsel of ROW_SEL is adjusted to drive the silicon-based OLED microdisplay's driving circuit to avoid bright spot defects and ensure that grayscale is not lost.

[0041] Furthermore, the unit pixel driving circuit includes input terminals DATA_in and ROW_SEL. Through a switching structure, a driving structure, and a holding structure, the electrical signal is converted into an optical signal by the OLED light-emitting device to achieve self-emission.

[0042] Furthermore, the switching structure is an NMOS transistor T1, the holding structure is a capacitor C, and the driving structure is an NMOS transistor T2, wherein:

[0043] The source is connected to DATA_in, the gate of T1 is connected to the input terminal ROW_SEL, the drain of T1 is connected to capacitor C and the gate of T2, and the substrate is connected to GND.

[0044] One end of capacitor C is connected to the drain of T1 and the gate of T2, and the other end is connected to GND;

[0045] The gate of NMOS transistor T2 is connected to the drain of T1, the source is connected to the anode of the OLED, the cathode of the OLED is connected to the common negative voltage VCOM, the drain of T2 is connected to VDD, and the substrate is connected to GND.

[0046] When ROW_SEL is 1, T1 is turned on, and DATA_in is stored in capacitor C and held for one frame's time, i.e., VC. When VC is greater than the threshold voltage of T2, T2 acts as a source follower, Vn is equivalent to VC, and together with the negative voltage VCOM, it acts on both ends of the OLED, causing the OLED to emit the corresponding brightness and grayscale. Because the circuit of this invention uses only NMOS transistors, it avoids various risks associated with N-well processes, thus preventing bright spot defects.

[0047] In this embodiment, because NMOS has poor transmission capability for high levels, when transmitting a high level and Figure 2 When T1 is turned on, VC≈VDATA_in-Vth, which may lead to the loss of high grayscale levels. Increasing the scan gate voltage Vsel of T1 to a range that meets the requirements for high-level transmission can improve this problem.

[0048] Meanwhile, due to the constraints imposed by semiconductor processes on the operating voltage range, excessively high Vsel may lead to gate breakdown; conversely, excessively low Vsel may cause premature VC saturation, resulting in the loss of high grayscale levels. Therefore, this invention proposes the following driving method to find a suitable driving configuration that ensures circuit reliability without sacrificing grayscale and brightness performance:

[0049] A driving method for a pixel driving circuit of a silicon-based OLED microdisplay that avoids bright spot defects includes the following steps:

[0050] Step S1: Power on the drive circuit and initialize the circuit configuration;

[0051] Step S2: Adjust the VCOM voltage by modifying the register configuration;

[0052] Step S3: By modifying the data of the built-in test video signal, adjust the display to 255 grayscale and test the corresponding brightness;

[0053] Step S4: By modifying the data of the built-in test video signal, adjust the display to 252 grayscale levels and test the corresponding brightness;

[0054] Step S5: Determine whether there is a significant difference in grayscale display brightness. If there is a significant difference, proceed to step S7; otherwise, proceed to step S6.

[0055] Step S6: By modifying the register configuration, adjust the CONTROL signal, increase the voltage Vsel of ROW_SEL, and continue to step S4;

[0056] Step S7: Adjust the GAMMA curve by modifying the register configuration to improve the display effect;

[0057] Step S8: Complete driver configuration.

[0058] like Figure 4 As shown, Figure 4 1 is without Figure 3 The voltage value of capacitor VC in the driving configuration shown is mapped to any gray level (the maximum gray level is 255 in this implementation). Figure 4 In section 2, the voltage value of the capacitor VC configured by the driver is mapped to any grayscale value. Figure 4 Figure 3 shows the mapping relationship between the capacitor voltage VC of the 3T1C and any grayscale level. It can be seen that the capacitor voltage VC is positively correlated with the OLED's luminous intensity. Therefore, if the pixel driving circuit of the silicon-based OLED microdisplay, which avoids bright spot defects, is not configured to drive the pixels, high grayscale information will be lost, resulting in a deterioration in display quality. After configuration using the driving method described in this invention, the display quality is consistent with that of the 3T1C model, and it also has the yield advantage of avoiding bright spot defects.

[0059] Example 2: This example uses a silicon-based OLED microdisplay with 8-bit grayscale display as an example to illustrate the pixel driving circuit and driving method for avoiding bright spot defects described in this invention.

[0060] In this embodiment, the driving power supply VDD is 5.0V, the common cathode voltage VCOM is -2.5V, and the voltage range of the input data signal DATA_in is 0V to 5.0V, corresponding to a grayscale display of 0 to 255.

[0061] In this embodiment, the input grayscale is converted into DATA_in voltage, where grayscale 0 corresponds to 0V, grayscale 255 corresponds to 5.0V, and intermediate grayscales generate corresponding data voltages according to a preset mapping relationship.

[0062] The unit pixel driving circuit adopts Figure 2 The diagram shows an all-NMOS structure, where T1 is the switching transistor, T2 is the driving transistor, and C is the holding capacitor. The boost module generates a scanning gate voltage Vsel based on the CONTROL signal and applies it to the ROW_SEL signal to improve the transmission capability of the switching transistor T1 for high-level signals.

[0063] In this embodiment, the boost module can output different scanning gate voltages Vsel according to the CONTROL configuration, for example:

[0064] When CONTROL=000, Vsel is 5.0V;

[0065] When CONTROL=001, Vsel is 5.5V;

[0066] When CONTROL=010, Vsel is 6.0V;

[0067] When CONTROL=011, Vsel is 6.5V;

[0068] When CONTROL=100, Vsel is 7.0V.

[0069] During driver configuration, first complete the driver circuit initialization and set VCOM to the preset operating voltage.

[0070] Subsequently, the monitor was made to display 255 gray levels using the built-in test image, and the corresponding brightness was recorded; then it was switched to 252 gray levels, and the corresponding brightness was recorded.

[0071] When Vsel is 5.0V, since the switching transistor T1 is an NMOS device, its high-level transmission capability is affected by the threshold voltage. When DATA_in approaches the full-scale voltage, the storage voltage VC on the holding capacitor C cannot continue to increase linearly with the increase of DATA_in, resulting in compression of the high grayscale region. At this time, the brightness difference between grayscale 255 and grayscale 252 is small, and high grayscale information cannot be effectively distinguished.

[0072] Subsequently, the CONTROL configuration was gradually increased, causing Vsel to gradually rise. When Vsel increased to approximately 6.0V, the effective overdrive voltage of the switching transistor T1 increased, allowing the data voltage corresponding to higher grayscale levels to be written more fully into the holding capacitor C. At this point, the brightness corresponding to grayscale levels 255 and 252 could be clearly distinguished, and the brightness of each grayscale level maintained a monotonically increasing relationship, with no obvious compression phenomenon in the high grayscale region.

[0073] When Vsel is further increased to above 6.5V, the improvement in display brightness is limited, while the scan gate voltage approaches the upper limit of the device's allowable operating range. Therefore, in this embodiment, Vsel of approximately 6.0V is preferred as the operating point.

[0074] After determining the scanning gate voltage, the brightness distribution of each gray level can be further corrected by adjusting the Gamma parameter in the display driving system, so that the display effect is comparable to that of the traditional 3T1C pixel driving structure.

[0075] With the above configuration, the present invention can improve the high grayscale data writing capability and avoid the loss of high grayscale information when using a full NMOS pixel driving structure. At the same time, it avoids the N-well process sensitivity problem introduced by using PMOS devices, thereby reducing the probability of bright spot defects and taking into account display brightness, grayscale integrity and circuit reliability.

Claims

1. A pixel driving circuit for a silicon-based OLED microdisplay that avoids bright spot defects, characterized in that, Includes a boost module and a unit pixel driving circuit; The boost module performs programmable boosting of the scanning gate voltage according to the control signal; The unit pixel driving circuit adopts an all-NMOS structure.

2. The silicon-based OLED microdisplay pixel driving circuit for avoiding bright spot defects as described in claim 1, characterized in that, The boost module includes input terminals CONTROL and VDD, and output terminal Vsel; the module programmatically boosts the VDD voltage according to the CONTROL signal to generate Vsel. By adjusting the CONTROL value, the voltage Vsel of ROW_SEL is adjusted to drive the silicon-based OLED microdisplay's driving circuit to avoid bright spot defects and ensure that grayscale is not lost.

3. The silicon-based OLED microdisplay pixel driving circuit for avoiding bright spot defects as described in claim 1, characterized in that, The unit pixel driving circuit includes input terminals DATA_in and ROW_SEL. Through a switching structure, driving structure, and holding structure, the electrical signal is converted into an optical signal by the OLED light-emitting device to achieve self-emission.

4. The silicon-based OLED microdisplay pixel driving circuit for avoiding bright spot defects as described in claim 1, characterized in that, The switching structure is an NMOS transistor T1, the holding structure is a capacitor C, and the driving structure is an NMOS transistor T2, wherein: The source is connected to DATA_in, the gate of T1 is connected to the input terminal ROW_SEL, the drain of T1 is connected to capacitor C and the gate of T2, and the substrate is connected to GND. One end of capacitor C is connected to the drain of T1 and the gate of T2, and the other end is connected to GND; The gate of NMOS transistor T2 is connected to the drain of T1, the source is connected to the anode of the OLED, the cathode of the OLED is connected to the common negative voltage VCOM, the drain of T2 is connected to VDD, and the substrate is connected to GND.

5. A driving method for a silicon-based OLED microdisplay pixel driving circuit to avoid bright spot defects as described in claim 1, comprising the following steps: Step S1: Power on the drive circuit and initialize the circuit configuration; Step S2: Adjust the VCOM voltage by modifying the register configuration; Step S3: By modifying the data of the built-in test video signal, adjust the display to 255 grayscale and test the corresponding brightness; Step S4: By modifying the data of the built-in test video signal, adjust the display to 252 grayscale levels and test the corresponding brightness; Step S5: Determine whether there is a significant difference in grayscale display brightness. If there is a significant difference, proceed to step S7; otherwise, proceed to step S6. Step S6: By modifying the register configuration, adjust the CONTROL signal, increase the voltage Vsel of ROW_SEL, and continue to step S4; Step S7: Adjust the GAMMA curve by modifying the register configuration to improve the display effect.

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