Charge compensation method and circuit for TFT display system

Abstract

The invention provides a charge compensation method and circuit for a TFT display system, and the method comprises the steps: receiving a charge signal through a TFT switch at a signal input stage, and recording an error charge quantity introduced by the TFT switch during the switching of a switch state; an array of proportional compensation capacitors, the lower plate of each compensation capacitor being connected to a high reference voltage or a low reference voltage; according to a preset time sequence and the error charge quantity, a lower pole plate of the compensation capacitor array is connected to a corresponding reference voltage through the control switch so as to adjust the voltage difference between the two ends of the compensation capacitor, so that the stored charge quantity is changed, the stored charge quantity is enabled to be equal to the error charge quantity, and charge compensation is realized. Aiming at the error problem caused by a TFT switch charge injection effect in a high-precision display system, the charge compensation is directly carried out at the front end of a signal chain, namely a signal input stage, by utilizing the most basic charge storage characteristic of the starting capacitor, the principle is simple, the circuit is relatively direct to realize, and the hardware cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a charge compensation method and circuit for a TFT display system. Background Art

[0002] Due to its fast response and clear visibility, TFT is widely used in various display systems as a switch to control pixels. Among them, the imaging system that uses integrated circuit chips to capture and quantify sensor charges is more sensitive to charge. The charge injected into the chip by the TFT switch integrated in each pixel of the display screen during the high-speed switching process will have a great impact on the system accuracy. Under the development trend and requirements of high precision, high speed and high integration in the field of sensor imaging, how to alleviate the charge error problem at the interface between TFT and conventional CMOS manufacturing process chips is becoming more and more important. A reasonable solution should be able to be directly compatible with CMOS circuits, offset the error charge without adding more hardware costs, realize charge compensation, and improve quantization accuracy and imaging quality.

[0003] A circuit capable of capturing switch charge injection and comparator kickback effects is disclosed in patent document with publication number CN118249813A. Figure 1 It is the core circuit to realize this scheme. This circuit is usually in the front stage of high-precision ADC, connected in parallel with the main signal path and connected to the input of the comparator. In the configuration stage, there is no signal in the main path, and normal switching action and timing are performed, and the non-zero code value obtained by the ADC at this time is stored; this code value directly reflects the error caused by factors such as switch charge injection, PVT fluctuation, comparator kickback, offset voltage, etc. in the entire path. In the working stage, this code value will be converted into the control signal of the switch array shown in the figure by a certain algorithm, and it will switch back and forth between the two states in conjunction with the actual working timing, and the electrical properties of the positive and negative reference voltages and capacitors are used to achieve the effect of offsetting the error amount before each main signal quantization.

[0004] The working principle of the imaging or display system of the sensor is essentially to capture and quantify tiny amounts of charge. Depending on the application scenario, the target value may be as low as a few pC (the unit of charge: picocoulomb, i.e. 10 -12 Coulomb), usually no more than a hundred pC. Precisely because the goal is to process such a small signal, CMOS integrated circuits are required to participate in this process. However, TFTs, which have many advantages in display, such as good visibility, fast response, and strong pixel control independence, are prone to errors in charge. This is because the channel that exists when the switch is turned on disappears after it is turned off, and the charge in it can only be released to both sides of the switch, which is unavoidable. Under the fine range of the pC level, the charge effect generated by the TFT switch cannot be ignored for the subsequent signal processing process of the CMOS integrated circuit.

[0005] Therefore, it is necessary to propose a new technical solution to improve the above technical problems. Summary of the invention

[0006] In view of the defects in the prior art, an object of the present invention is to provide a charge compensation method and circuit for a TFT display system.

[0007] According to a charge compensation method for a TFT display system provided by the present invention, the method comprises:

[0008] In the signal input stage, the charge signal is received through the TFT switch, and the error charge amount introduced by the TFT switch is recorded when the switch state is switched;

[0009] A proportional compensation capacitor array is configured, wherein the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage;

[0010] According to the preset timing and error charge amount, the lower plate of the compensation capacitor array is connected to the corresponding reference voltage by controlling the switch to adjust the voltage difference across the compensation capacitor, thereby changing the stored charge amount so that the stored charge amount is equal to the error charge amount, thereby realizing charge compensation.

[0011] Preferably, in a proportional compensation capacitor array, normal switching action and timing are performed when there is no signal input, and the error charge introduced by the TFT switch is captured and quantified by an analog-to-digital converter ADC;

[0012] The quantized error charge is converted into a digital code value and pre-stored in the control logic to be used as the basis for generating control signals in subsequent work.

[0013] Preferably, the capacitance value and quantity of the compensation capacitor array and the difference between the high reference voltage and the low reference voltage are designed according to actual needs to adjust the compensation range and accuracy.

[0014] Preferably, bidirectional compensation of positive charge and negative charge is achieved by changing the phase of the switch control signal.

[0015] The present invention also provides a charge compensation circuit, which implements the charge compensation method for a TFT display system, including: a TFT switch, a compensation capacitor array and a control logic;

[0016] One end of the TFT switch is connected to the input end of the sensor, and the other end is respectively connected to the compensation capacitor array and the charge capture circuit; the other end of the compensation capacitor array is connected to the compensation switch array; the other end of the compensation switch array is respectively connected to the high reference voltage and the low reference voltage.

[0017] Preferably, the TFT switch is used to receive a charge signal;

[0018] The compensation capacitor array comprises a plurality of proportional compensation capacitors, and the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage through a corresponding switch;

[0019] The control logic generates a control signal to control the state of the switch according to a preset timing and a pre-stored digital code value of the error charge, thereby adjusting the charge storage amount of the compensation capacitor array to achieve charge compensation.

[0020] Preferably, an analog-to-digital converter ADC is further included for capturing and quantifying the amount of error charge introduced by the TFT switch during the configuration stage.

[0021] Preferably, the capacitance value, the number of the compensation capacitor array and the difference between the high and low reference voltages are set according to compensation requirements.

[0022] Preferably, the TFT switch is a single-pole double-throw switch, which is controlled by a pair of non-overlapping inverting logic signals, and only one switch is turned on at the same time.

[0023] Preferably, the compensation capacitor array includes compensation capacitor C, compensation capacitor kC and compensation capacitor k 2 C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention aims at the error problem caused by the charge injection effect of TFT switches in high-precision display systems. It utilizes the most basic charge storage characteristics of capacitors to directly perform charge compensation at the front end of the signal chain, i.e., the signal input stage. The principle is simple, the circuit implementation is relatively direct, and the hardware cost is low.

[0026] 2. The number and capacitance of the compensation capacitor array of the present invention can be adjusted according to actual conditions, and the high and low reference voltages are combined to make the compensation range and accuracy flexible;

[0027] 3. The present invention can also achieve bidirectional compensation by simply changing the phase of the switch control signal according to the different polarities of the injected charge;

[0028] 4. The present invention can easily expand its functions to compensate for the charge errors caused by other non-ideal factors; after compensation, the output accuracy and imaging quality of the display system will be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0030] Figure 1A schematic diagram of a circuit implementation of the existing charge injection and recoil effect capture technology;

[0031] Figure 2 A schematic diagram of a circuit implementation of the charge compensation solution of the present invention;

[0032] Figure 3 It is a schematic diagram of an implementation method of the technical solution of the present invention;

[0033] Figure 4 This is a schematic diagram of the working status of this patented technical solution. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0035] Embodiment 1:

[0036] Reference Figure 2 and Figure 3 According to a charge compensation method for a TFT display system provided by the present invention, the method comprises:

[0037] In the signal input stage, the charge signal is received through the TFT switch, and the error charge amount introduced by the TFT switch is recorded when the switch state is switched;

[0038] A proportional compensation capacitor array is configured, wherein the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage;

[0039] According to the preset timing and error charge amount, the lower plate of the compensation capacitor array is connected to the corresponding reference voltage by controlling the switch to adjust the voltage difference across the compensation capacitor, thereby changing the stored charge amount so that the stored charge amount is equal to the error charge amount, thereby realizing charge compensation.

[0040] In the proportional compensation capacitor array, normal switching actions and timing are performed when there is no signal input, and the error charge introduced by the TFT switch is captured and quantified through the analog-to-digital converter ADC; the quantized error charge is converted into a digital code value and pre-stored in the control logic, which is used as the basis for generating control signals in subsequent work.

[0041] The capacitance value and quantity of the compensation capacitor array and the difference between the high reference voltage and the low reference voltage are designed according to actual needs to adjust the compensation range and accuracy. By changing the phase of the switch control signal, bidirectional compensation of positive and negative charges can be achieved.

[0042] The present invention also provides a charge compensation circuit, which implements the charge compensation method for a TFT display system, including: a TFT switch, a compensation capacitor array and a control logic;

[0043] One end of the TFT switch is connected to the input end of the sensor, and the other end is respectively connected to the compensation capacitor array and the charge capture circuit; the other end of the compensation capacitor array is connected to the compensation switch array; the other end of the compensation switch array is respectively connected to the high reference voltage and the low reference voltage.

[0044] The TFT switch is used to receive the charge signal; the compensation capacitor array includes a plurality of proportional compensation capacitors, and the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage through a corresponding switch; the control logic generates a control signal to control the state of the switch according to the preset timing and the pre-stored digital code value of the error charge, thereby adjusting the charge storage amount of the compensation capacitor array to achieve charge compensation; it also includes an analog-to-digital converter ADC, which is used to capture and quantify the error charge introduced by the TFT switch during the configuration stage. The capacitance value, number, and difference between the high and low reference voltages of the compensation capacitor array are set according to compensation needs. The TFT switch is a single-pole double-throw switch controlled by a pair of non-overlapping inverting logic signals, and only one switch is turned on at the same time. The compensation capacitor array includes compensation capacitor C, compensation capacitor kC, and compensation capacitor k 2 C.

[0045] Embodiment 2:

[0046] The solution to be described in this patent is to solve the error problem of charge injection and provide a circuit structure that can be integrated and manufactured using CMOS technology. After addition, charge compensation can be achieved at a relatively low hardware cost, thereby improving system accuracy and imaging quality.

[0047] One implementation of the solution described in this patent is as follows Figure 2Circuit in dotted box. The lower plates of proportional compensation capacitors 203, 204, 205, etc. can be independently selected to be connected to one of the high and low reference voltages through their corresponding switches 213, 214, 215, etc. When the charge signal is input, the TFT switch 202 will change the on / off state, inevitably introducing errors to the original signal. At this time, by controlling switches 213, 214, 215, etc. with a good timing, the reference voltage selected to be connected to the lower plate of the compensation capacitor changes. Since the charge capture circuit usually has the property of clamping the input terminal voltage, the aforementioned change will cause the voltage difference across the compensation capacitor to change, that is, the amount of stored charge to change. By reasonably modulating the difference between the two reference voltages and using the switch control signal to change the actual number of capacitors involved in the state switching, the storage amount can be made equal to the introduced error amount, thereby achieving the purpose of charge compensation. From the perspective of the circuit, the error charge injected by the TFT switch 202 is just stored by the compensation capacitor array, and at this time, the charge capture circuit receives the actual signal charge amount. The proportionality factor k in the figure is an optional value and should be determined in the design stage; in order to facilitate the correspondence of binary digital code values ​​in the signal and error charge quantization process, k = 2 or 1 / 2 is a common choice, and other values ​​can also be designed according to actual conditions. The number of compensation capacitors also has design freedom, and only three are drawn here; changing the number of capacitors allows the design to balance hardware cost, compensation range and accuracy.

[0048] Compared with the aforementioned existing technical solutions that compensate at the step of ADC quantizing the voltage value, this solution directly eliminates the error at an earlier stage of the signal chain, that is, when the charge is input, and uses the property that the charge stored in the capacitor is proportional to the voltage difference between the two ends to ensure the consistency of the compensation and the integrity of the subsequent circuit structure as much as possible. In addition, under the premise of the same number of bits, the number of compensation capacitors in this solution is relatively reduced by half, reducing the circuit complexity and hardware cost; the difference between the high and low reference voltages can be adjusted according to actual needs, so that the compensation range and accuracy have a certain degree of flexibility; the symmetry of the two reference voltages also makes the compensation of positive and negative charges feasible, and bidirectional charge compensation can be achieved by simply inverting the switch control signal.

[0049] Figure 3 and Figure 4 A possible implementation method and working state switching are shown. The circuit elements required for this solution include four parts: TFT switch 202, compensation capacitor 203, etc., selection switch 213, etc., and switch control logic (not shown in the figure); in addition, high reference voltage 221 and low reference voltage 222 are required to participate in the charge compensation process.

[0050] First, the entire circuit is made to go through normal working sequence, and the charge amount injected by the switch 202 is calculated by combining the manufacturing process and physical parameters of the TFT switch with the help of the charge capture circuit and quantization module such as ADC. Combined with the subsequent actual design value, it is converted into a digital code value and stored in advance.

[0051] Determine each design value so that the target compensation amount can be included, and at the same time, the accuracy is not insufficient due to the large range. In this embodiment, C = 0.5pF, each compensation capacitor value is 0.5pF, 1pF, 2pF, the high reference voltage is 1.0V, and the low reference voltage is 0.8V. The maximum compensable range is ±0.7pC, and the adjustable step size is 0.1pC; since the number and size of capacitors and switches cannot be modified after the design is completed, further fine-tuning can be achieved by changing the two reference voltages.

[0052] In the embodiment, the TFT switch 202 is a P-type channel, and will release about 0.5pC positive charge to the circuits on both sides at the moment of shutoff; it can be seen from the above design values ​​that capacitors 203 and 205 will participate in the compensation process, and switches 213 and 215 should follow the timing changes of the TFT switch 202 while the state of switch 214 remains unchanged. Therefore, the switch control logic should be affected by the real-time changing TFT switch timing and the fixed pre-stored code value, and a set of digital signals with timing are generated to determine the state of switches 213 to 215. For a reference voltage that is not too high, in order to achieve a better conduction effect, these switches themselves can be implemented as two NMOS, controlled by a pair of non-overlapping inverting logic signals, and only one of them is turned on at the same time, thus completing the gating function of the single-pole double-throw switch. Under the 180nm standard CMOS process, the NMOS of the three switches are designed to have a length of 300nm to avoid leakage caused by the minimum channel length; the two NMOS of switch 213 are designed to have a width of 3um, the switch 214 is designed to have a width of 6um, and the switch 215 is designed to have a width of 12um, which are proportional to the capacitances they control, that is, the amount of charge to be discharged is approximately proportional to the switch conduction capacity, so that the transient response on each capacitor branch is as consistent as possible.

[0053] Figure 4 The dotted line in the middle indicates the path for the error charge to flow. The state switching of switches 213 and 215 causes the voltage of the lower plates of capacitors 203 and 205 to drop by 0.2V, while the voltage of the upper plates, as signal interfaces and input nodes of the charge capture circuit, will be relatively stable due to the clamping effect, so that the positive charge stored in the upper plates of the two capacitors increases by 2.5pF×0.2V=0.5pC in total; from the perspective of signal charge capture, the charge injected by the TFT switch is just stored by this part of the capacitor, and only the real signal charge enters the main signal path normally, that is, the charge compensation function is completed.

[0054] The present invention aims at the error problem caused by the charge injection effect of the TFT switch in the high-precision display system. It utilizes the most basic charge storage characteristics of the capacitor and directly performs charge compensation at the front end of the signal chain, that is, the signal input stage. The principle is simple, the circuit implementation is relatively direct, and the hardware cost is low. The number and capacitance design of the compensation capacitor array can be adjusted according to the actual situation, and the high and low reference voltages are combined to make the compensation range and accuracy flexible. According to the different polarities of the injected charge, bidirectional compensation can also be achieved by simply changing the phase of the switch control signal; therefore, the solution is also easy to expand functions to compensate for charge errors caused by other non-ideal factors. After compensation, the output accuracy and imaging quality of the display system will be significantly improved.

[0055] NMOS: N-Metal-Oxide-Semiconductor: N-type field effect transistor

[0056] PMOS: P-Metal-Oxide-Semiconductor: P-type field effect transistor

[0057] CMOS: Complementary-Metal-Oxide-Semiconductor

[0058] TFT: Thin-Film-Transistor

[0059] ADC: Analog-to-Digital-Converter

[0060] PVT: Process-Voltage-Temperature: process, voltage, temperature

[0061] MIM: Metal-Insulator-Metal: Metal-Insulator-Metal Capacitor / Plate Capacitor

[0062] Those skilled in the art may understand this embodiment as a more specific description of Embodiment 1.

[0063] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0064] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A charge compensation method for a TFT display system, characterized in that: The method comprises: In the signal input stage, the charge signal is received through the TFT switch, and the error charge amount introduced by the TFT switch is recorded when the switch state is switched; A proportional compensation capacitor array is configured, wherein the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage; According to the preset timing and error charge amount, the lower plate of the compensation capacitor array is connected to the corresponding reference voltage by controlling the switch to adjust the voltage difference across the compensation capacitor, thereby changing the stored charge amount so that the stored charge amount is equal to the error charge amount, thereby realizing charge compensation.

2. The charge compensation method for a TFT display system according to claim 1, characterized in that: In a proportional compensation capacitor array, normal switching action and timing are performed when there is no signal input, and the error charge introduced by the TFT switch is captured and quantified through the analog-to-digital converter ADC; The quantized error charge is converted into a digital code value and pre-stored in the control logic to serve as the basis for generating control signals in subsequent work.

3. The charge compensation method for a TFT display system according to claim 1, characterized in that: The capacitance value and quantity of the compensation capacitor array and the difference between the high reference voltage and the low reference voltage are designed according to actual needs to adjust the compensation range and accuracy.

4. The charge compensation method for a TFT display system according to claim 1, characterized in that: By changing the phase of the switch control signal, bidirectional compensation of positive and negative charges can be achieved.

5. A charge compensation circuit, characterized in that: The circuit implements the charge compensation method for a TFT display system according to any one of claims 1 to 4, comprising: a TFT switch, a compensation capacitor array, and control logic; One end of the TFT switch is connected to the input end of the sensor, and the other end is respectively connected to the compensation capacitor array and the charge capture circuit; the other end of the compensation capacitor array is connected to the compensation switch array; the other end of the compensation switch array is respectively connected to the high reference voltage and the low reference voltage.

6. The charge compensation circuit according to claim 5, characterized in that: The TFT switch is used to receive a charge signal; The compensation capacitor array comprises a plurality of proportional compensation capacitors, and the lower plate of each compensation capacitor is connected to a high reference voltage or a low reference voltage through a corresponding switch; The control logic generates a control signal to control the state of the switch according to a preset timing and a pre-stored digital code value of the error charge, thereby adjusting the charge storage amount of the compensation capacitor array to achieve charge compensation.

7. The charge compensation circuit according to claim 6, characterized in that: An analog-to-digital converter (ADC) is also included to capture and quantify the amount of error charge introduced by the TFT switching during the configuration phase.

8. The charge compensation circuit according to claim 5, characterized in that: The capacitance value, quantity and difference between high and low reference voltages of the compensation capacitor array are set according to compensation requirements.

9. The charge compensation circuit according to claim 5, characterized in that: The TFT switch is a single-pole double-throw switch, which is controlled by a pair of non-overlapping inverting logic signals, and only one switch is turned on at the same time.

10. The charge compensation circuit according to claim 5, characterized in that: The compensation capacitor array includes compensation capacitor C, compensation capacitor kC and compensation capacitor k 2 C.

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