Constant current driving circuit, driver and display device

Abstract

The embodiment of the invention provides a constant-current driving circuit, a driver and a display device, the constant-current driving circuit comprises a switch module, a sampling module, an operational amplifier and a feedback module, the sampling module is used for determining feedback voltage of a branch where a light-emitting module is located, amplification processing is performed through the feedback module, an in-phase input end of the operational amplifier module receives analog voltage, and the in-phase input end of the operational amplifier module outputs the analog voltage; when the analog voltage is the amplified voltage, the inverted input end receives the amplified feedback voltage, and when the analog voltage is the amplified voltage, the two input ends of the operational amplification module receive the amplified voltage, so that the influence of the offset voltage of the operational amplification module on the output current of the light-emitting driver can be reduced, and the precision of the output current of the light-emitting driver is improved.

Description

Technical Field

[0001] This application relates to the field of chip drivers, and more particularly to a constant current driving circuit, a driver, and a display device. Background Technology

[0002] In LED (Light Emitting Diode) backlight display systems, high-precision LED constant current drive circuits are the core components for achieving display quality.

[0003] Linear constant current drive circuits are widely used in display devices due to their simple structure, low cost, and good current consistency.

[0004] However, existing linear constant current drive currents have low accuracy, and the main reason for the limited accuracy is the error caused by the offset of the operational amplifier. Summary of the Invention

[0005] This application provides a constant current drive circuit, a driver, and a display device to reduce the impact of operational amplifier offset and improve output current accuracy.

[0006] In a first aspect, embodiments of this application provide a constant current drive current, including:

[0007] A switch module, the first end of which is connected to a light-emitting module and used to control the light-emitting state of the light-emitting module;

[0008] A sampling module, wherein the first end of the sampling module is connected to the second end of the switching module and the second end of the sampling module is grounded, is used to determine the feedback voltage of the branch corresponding to the light-emitting module when the switching module is in the on state;

[0009] An operational amplifier module is provided, wherein the non-inverting input terminal of the operational amplifier module receives an analog voltage, and the output terminal of the operational amplifier module is connected to the control terminal of the switching module for controlling the switching state of the switching module.

[0010] The feedback module has its input terminal connected to the first terminal of the sampling module and its output terminal connected to the inverting input terminal of the operational amplifier module. It is used to amplify the feedback voltage so as to reduce the influence of the offset voltage of the operational amplifier module on the output current of the light-emitting drive when the analog voltage is the amplified voltage.

[0011] Optionally, the feedback module includes:

[0012] An amplification unit is provided, wherein the first input terminal of the amplification unit is connected to the input terminal of the feedback module, and the output terminal of the amplification unit is connected to the output terminal of the feedback module, for amplifying the feedback voltage;

[0013] A gain adjustment unit is provided, with its first end connected to the output end of the amplification module and its second end connected to the second input end of the amplification module, for determining the amplification factor of the feedback voltage.

[0014] Optionally, the amplification unit includes:

[0015] A first operational amplifier, wherein the non-inverting input terminal of the first operational amplifier serves as the first input terminal of the amplification unit, the inverting input terminal of the first operational amplifier serves as the second input terminal of the amplification unit, and the output terminal of the first operational amplifier serves as the output terminal of the amplification unit;

[0016] The gain adjustment unit includes:

[0017] The first resistor is connected between the inverting input terminal and the output terminal of the first operational amplifier.

[0018] The second resistor is connected between the inverting input of the first operational amplifier and ground.

[0019] Optional, also includes:

[0020] A modulation module, connected between the input and output terminals of the feedback module, is used to suppress the offset voltage of the first operational amplifier.

[0021] Optionally, the modulation module includes:

[0022] An input chopper modulator is connected between the input terminal of the feedback module and the non-inverting input terminal of the first operational amplifier, and is used to modulate the feedback voltage input to the first operational amplifier.

[0023] An output chopper modulator is connected between the output terminal of the first operational amplifier and the output terminal of the feedback module to demodulate the output voltage of the first operational amplifier in order to suppress the offset voltage of the first operational amplifier.

[0024] Optional, also includes:

[0025] The transient enhancement module is connected to the control terminal of the switching module;

[0026] The transient enhancement module is used to provide a first transient current to the control terminal of the switch module at the moment the switch module is turned on, so as to accelerate the voltage rise of the control terminal of the switch module.

[0027] And / or, to draw a second transient current from the control terminal of the switch module at the instant the switch module is turned off, so as to accelerate the voltage drop at the control terminal of the switch module.

[0028] Optionally, the transient enhancement module includes:

[0029] A pull-up current source, the output terminal of which is connected to the control terminal of the switching module, is used to provide the first transient current;

[0030] A pull-down current source, the input terminal of which is connected to the control terminal of the switching module, is used to extract the second transient current.

[0031] Optional, also includes:

[0032] A bandgap reference source is used to provide a reference voltage;

[0033] A digital-to-analog converter, connected to the output of the bandgap reference source and the non-inverting input of the operational amplifier module, is used to output the analog voltage based on the reference voltage and the digital control signal.

[0034] Secondly, this application provides a driver that includes the constant current driving circuit described in the first aspect.

[0035] Thirdly, this application provides a display device including the driver described in the second aspect.

[0036] The constant current driving circuit, driver, and display device provided in this application include a switching module, a sampling module, an operational amplifier, and a feedback module. The sampling module is used to determine the feedback voltage of the branch where the light-emitting module is located. After amplification by the feedback module, the non-inverting input terminal of the operational amplifier module receives the analog voltage, and the inverting input terminal receives the amplified feedback voltage. When the analog voltage is the amplified voltage, both input terminals of the operational amplifier module receive the amplified voltage, which can reduce the influence of the offset voltage of the operational amplifier module on the output current of the light-emitting driver and improve the output current accuracy of the light-emitting driver. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0038] Figure 1 This is a schematic diagram of a constant current drive circuit.

[0039] Figure 2 Schematic diagram of the constant current drive circuit provided in this application Figure 1 ;

[0040] Figure 3 Schematic diagram of the constant current drive circuit provided in this application Figure 2 ;

[0041] Figure 4 Schematic diagram of the constant current drive circuit provided in this application Figure 3 ;

[0042] Figure 5 A circuit diagram of the pull-up current source provided in this application;

[0043] Figure 6 A circuit diagram of the pull-down current source provided in this application;

[0044] Figure 7 A circuit diagram of the bias voltage generating unit provided in this application.

[0045] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0046] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0047] In LED (Light Emitting Diode) backlight display systems, high-precision LED constant current drive circuits are the core components for achieving display quality.

[0048] There are three main types of existing constant current drivers:

[0049] 1. Switching circuit

[0050] A switching converter circuit converts the input voltage into an output voltage that is different from the input voltage and is required by the load by controlling the on and off states of the power switching transistors to periodically store and release energy in the inductors and capacitors.

[0051] Switching converter circuits employ a closed-loop negative feedback mechanism to achieve constant current output. They primarily have three basic topologies: BUCK, BOOST, and BUCKBOOST. BUCK refers to a buck converter, which converts the input voltage to an output voltage lower than the input voltage. BOOST refers to a boost converter, which converts the input voltage to an output voltage higher than the input voltage. BUCKBOOST refers to a buck-boost converter, where the output voltage can be lower or higher than the input voltage, and the polarities are usually opposite (i.e., the output voltage and input voltage are out of phase).

[0052] The energy loss of switching converter circuits mainly consists of the turn-off loss and conduction loss of the power switching transistors. The energy conversion efficiency is very high, reaching over 90%, and it also has a large input voltage range and load range. It is currently widely used in LED lighting display systems.

[0053] However, switching converter circuits have a complex structure, require consideration of electromagnetic compatibility issues, and are relatively expensive. Furthermore, the output current of switching converter circuits exhibits variability and poor current consistency. Additionally, the use of inductors occupies a significant amount of space, limiting the application of switching converter circuits in some low-power LED display and decorative driving applications.

[0054] 2. Charge pump drive circuit

[0055] The charge pump drive circuit, also known as a switched capacitor boost controller, stores energy and achieves the boost function by controlling the charging and discharging of the capacitor through a switch.

[0056] The charge pump drive circuit can achieve constant current output using a closed-loop negative feedback method. It uses capacitor energy storage, eliminating the need for inductors, effectively saving chip area and reducing costs. Furthermore, it features low static power consumption, low electromagnetic interference, and high efficiency, and is currently widely used in low-to-medium power white LED driver circuits.

[0057] However, the charge pump drive circuit uses a large number of capacitors to control the output current, which also occupies a large chip area.

[0058] 3. Linear constant current drive circuit

[0059] A linear constant current drive circuit is a simple and easy-to-use method for driving LEDs with constant current. It consists of an operational amplifier, a power switch, and a sampling resistor. The operational amplifier adjusts the gate voltage of the power switch based on the output current sampled by the sampling resistor, thus achieving a constant current output. Linear drive circuits are simple in structure, low in cost, and offer good current consistency.

[0060] However, the inventors discovered through research that existing linear constant current drive currents, such as Figure 1As shown, its accuracy is relatively low, making it difficult to meet high-precision requirements. The main reason for the limited accuracy is the error caused by the offset of the operational amplifier.

[0061] Typically, to reduce power consumption and consider efficiency, the reference voltage Vref output by a bandgap reference source is between 200mV and 400mV. Meanwhile, to achieve high accuracy, the number of bits in a digital-to-analog converter (DAC) is generally 10 bits or even higher. When the reference voltage is 200mV, the least significant bit (LST) is only 0.195mV. The LST refers to the minimum change in analog output voltage corresponding to a change of one minimum count unit in the input digital code of the DAC. However, the offset voltage of an operational amplifier is typically 2mV-5mV. If the offset voltage far exceeds the LST voltage of the DAC, the brightness of the LED will essentially be out of control, thus affecting the accuracy of the output current.

[0062] For example, the inputs of the digital-to-analog converter include a digital control signal and a reference voltage output from a bandgap reference source; the digital control signal is an N-bit binary signal from a digital system such as an MCU, representing the digital ratio of the analog voltage to the reference voltage; the reference voltage is a fixed analog voltage provided by the bandgap reference source, which is the range reference for the digital-to-analog converter conversion and determines the maximum value of the analog voltage output by the digital-to-analog converter.

[0063] The analog voltage is then:

[0064]

[0065] Where D is a digital control signal (e.g., 8-bit number 00110101 corresponds to decimal 53). It is the full-scale digital value of the digital-to-analog converter (e.g., the full-scale value of an 8-bit DAC is 256).

[0066] Under closed-loop steady-state conditions, the virtual short characteristic of the operational amplifier (the voltages at the non-inverting and inverting inputs of an ideal op-amp are approximately equal) holds true. However, the offset voltage Vos1 must be considered, which determines the voltage at the non-inverting input of the op-amp. voltage at the inverting input of the op-amp (in, This refers to the voltage across the sampling resistor, also known as the feedback voltage. This refers to the output current of the LED driver, which can also be understood as the light-emitting current of the corresponding branch of the LED. It is a constant positive current provided to enable the LED to work normally; R refers to the resistance value of the sampling resistor.

[0067] From the virtual short, we can obtain: ,Right now: Correspondingly, the current in the branch where the LED is located is:

[0068]

[0069] As can be seen from the above formula, offset voltage will seriously affect the output current accuracy of LED driver.

[0070] To address this, this application proposes a constant current drive circuit, in which a feedback module is set between the sampling module and the inverting input of the operational amplifier module. The feedback module is used to amplify the feedback voltage to reduce the offset voltage of the operational amplifier module, thereby improving the output current accuracy of the light-emitting drive.

[0071] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0072] Figure 2 The schematic diagram of the constant current drive circuit provided in this application is as follows: Figure 2 As shown, the constant current drive circuit provided in this application includes:

[0073] Switching module 101, sampling module 102, operational amplifier module 103, and feedback module 104;

[0074] The first end of the switch module 101 is connected to the light-emitting module 20;

[0075] The first terminal of the sampling module 102 is connected to the second terminal of the switch module 101, and the second terminal of the sampling module 102 is grounded.

[0076] The non-inverting input terminal of the operational amplifier module 103 receives the analog voltage, and the output terminal of the operational amplifier module 103 is connected to the control terminal of the switching module 101.

[0077] The input terminal of the feedback module 104 is connected to the first terminal of the sampling module 102, and the output terminal of the feedback module 104 is connected to the inverting input terminal of the operational amplifier module.

[0078] The switching module 101 is used to control the light-emitting state of the light-emitting module 20; the sampling module 102 is used to determine the feedback voltage of the branch where the light-emitting module 20 is located when the switching module 101 is in the conducting state; the operational amplifier module 103 is used to control the switching state of the switching module 101; and the feedback module 104 is used to amplify the feedback voltage to reduce the offset voltage of the operational amplifier module 103 when the analog voltage is the amplified voltage.

[0079] In this embodiment, the switch module 101 includes a control terminal, a first terminal, and a second terminal. The sampling module 102 includes a first terminal and a second terminal. The first terminal of the switch module 101 is connected to the light-emitting module 20, and the second terminal of the switch module 101 is connected to the first terminal of the sampling module 102. The second terminal of the sampling module 102 is grounded. Therefore, the light-emitting module 20, the switch module 101, and the sampling module 102 can constitute the branch corresponding to the light-emitting module 20, i.e., the light-emitting branch.

[0080] The switch module 101 is used to control the light-emitting state of the light-emitting module 20, which can include emitting light and not emitting light. When the switch module 101 is in the on state, the light-emitting module 20 emits light; when the switch module 101 is in the off state, the light-emitting module 20 does not emit light.

[0081] Accordingly, the sampling module 102 is used to sample the current flowing through the light-emitting branch (referred to as the light-emitting current) or generate a corresponding sampling signal when the switch module 101 is in the on state, so as to determine the feedback voltage VFB of the branch corresponding to the light-emitting module 20. The feedback voltage VFB can be understood as the product of the light-emitting current and the resistance of the sampling module 102.

[0082] In this embodiment, the operational amplifier module 103 includes a non-inverting input, an inverting input, and an output; the feedback module 104 includes an input and an output. The non-inverting input of the operational amplifier module 103 receives an analog voltage, and the output of the operational amplifier module 103 is connected to the control terminal of the switching module 101. The input of the feedback module 104 is connected to the first terminal of the sampling module 102, and the output of the feedback module 104 is connected to the inverting input of the operational amplifier module 103. Therefore, the operational amplifier module 103, the switching module 101, the sampling module 102, and the feedback module 104 together constitute a negative feedback control loop, used to stabilize the luminous current at a target value set by the analog voltage.

[0083] Since the feedback module 104 is connected to the first end of the sampling module 102, the feedback module 104 can receive the feedback voltage VFB determined by the sampling module 102 and amplify the feedback voltage VFB. Accordingly, the output end of the feedback module 104 outputs the amplified feedback voltage, and the inverting input end of the operational amplifier module 103 receives the amplified feedback voltage.

[0084] The non-inverting input of the operational amplifier module 103 receives the analog voltage Vin, and the inverting input receives the amplified feedback voltage. When the analog voltage Vin is the amplified voltage, both inputs of the operational amplifier module 103 receive the amplified voltage, which reduces the impact of the offset voltage Vos1 of the operational amplifier module 103 on the output current of the light-emitting driver, thereby improving the accuracy of the output current of the light-emitting driver. The output current of the light-emitting driver can also be referred to as the light-emitting current of the light-emitting branch.

[0085] The operational amplifier module 103 sets the analog voltage Vin at its non-inverting input terminal as the current target reference, compares it with the feedback voltage VFB at its inverting input terminal, amplifies the difference between the two, and generates a control signal Nld_MOS. The control signal Nld_MOS is used to control the switching state of the switching module 101.

[0086] For example, if the output current of the light-emitting driver is too small, the feedback voltage VFB received at the inverting input terminal will be too small. Then, the control signal Nld_MOS output by the operational amplifier module 103 will be used to increase the conduction level of the switching module 101, thereby increasing the output current of the light-emitting driver. If the output current of the light-emitting driver is too large, the feedback voltage VFB received at the inverting input terminal will be too large. Then, the control signal Nld_MOS output by the operational amplifier module 103 will be used to decrease the conduction level of the switching module 101, thereby reducing the output current of the light-emitting driver.

[0087] It's important to note that an ideal op-amp satisfies the virtual short condition (the voltage at the non-inverting input equals the voltage at the inverting input), meaning the output voltage is zero when the two inputs are directly shorted. However, due to manufacturing defects in the op-amp's internal transistors (such as mismatch in the characteristics of differential pairs), even with the two inputs shorted and the input voltage zero, there will still be a slight DC voltage offset in the output voltage. To compensate for this offset and return the output voltage to zero, a reverse compensation voltage, also known as an offset voltage, needs to be applied between the inputs.

[0088] To illustrate the beneficial effects of this application, the following formula will be used for explanation:

[0089] Taking a feedback voltage amplification of K times as an example, the output current is:

[0090]

[0091] in, D is the reference voltage; D is the digital control signal. It is the full-scale digital value of the digital-to-analog converter; It is the offset voltage of the operational amplifier module; This is the gain factor, also known as the amplification factor. This is the resistor of the sampling module.

[0092] When the analog voltage is amplified by a factor of K, the output current is:

[0093]

[0094] Therefore, after the feedback module 104 amplifies the feedback voltage, and the analog voltage is also amplified, the offset voltage of the operational amplifier module 103 can be reduced. It should be noted that the amplified voltage is relative to... Figure 1 In terms of architecture, for example, if Figure 1 The analog voltage in is V DAC Therefore, the solution is K×V. DAC .

[0095] By introducing a feedback network with a gain of K and simultaneously amplifying the analog voltage by the same factor K, a symmetrical loop design is constructed. The ingenuity of this design lies in the fact that when the system reaches negative feedback equilibrium, the gain coefficient K is canceled out of the equation determining the output current magnitude, thus not affecting the output current setpoint. However, the offset voltage, as an error within the loop, is attenuated by the gain K, equivalent to Vos1 / K. Therefore, the gain K selectively and significantly suppresses the offset error without affecting the useful signal (current setpoint), thereby achieving an order-of-magnitude improvement in accuracy while maintaining the original current regulation range.

[0096] For example, the switch module 101 may include one or more switching transistors. When the switch module 101 includes one switching transistor, the first end of the switching transistor serves as the first end of the switch module 101, and the second end of the switching transistor serves as the second end of the switch module 101. When the switch module 101 includes multiple switching transistors, the multiple switching transistors are cascaded, with the first end of the first switching transistor serving as the first end of the switch module 101, and the second end of the last switching transistor serving as the second end of the switch module 101. Furthermore, in the cascaded relationship, the second end of the previous switching transistor is connected to the first end of the next switching transistor, and the previous and next switching transistors are adjacent switching transistors.

[0097] For example, the switching transistor is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). When the MOSFET is an NMOS, the drain of the NMOS is the first terminal of the switching transistor, and the source of the NMOS is the second terminal. When the MOSFET is a PMOS, the source of the PMOS is the first terminal of the switching transistor, and the drain of the PMOS is the second terminal. Switching transistors can also include IGBTs (Insulated Gate Bipolar Transistors).

[0098] For example, the sampling module 102 may include one or more resistors. When the sampling module 102 includes one resistor, the first end of the resistor serves as the first terminal of the sampling module 102, and the second end of the resistor serves as the second terminal of the sampling module 102. When the sampling module 102 includes multiple resistors, the multiple resistors are cascaded, with the first terminal of the first resistor serving as the first terminal of the sampling module 102, the second terminal of the last resistor serving as the second terminal of the sampling module 102, and the second terminal of the previous resistor connected to the first terminal of the next resistor in the cascaded relationship, with adjacent resistors of the previous and next resistors.

[0099] For example, the operational amplifier module 103 includes an operational amplifier, the non-inverting input terminal of the operational amplifier is used as the non-inverting input terminal of the operational amplifier module 103, the inverting input terminal of the operational amplifier module 103 is used as the inverting input terminal of the operational amplifier module 103, and the output terminal of the operational amplifier module 103 is used as the output terminal of the operational amplifier module 103.

[0100] The operational amplifier module 103 can also be implemented through discrete component construction, modular combination, or replacement with special function chips. For example, the internal structure of an integrated operational amplifier can be simulated by building a differential amplifier stage, a voltage amplifier stage, and an output stage using transistors.

[0101] Optional, such as Figure 4As shown, the feedback module 104 includes an amplification unit 1041 and a gain adjustment unit 1042. The first input terminal of the amplification unit 1041 is connected to the input terminal of the feedback module 104, and the output terminal of the amplification unit 1041 is connected to the output terminal of the feedback module 104. The first terminal of the gain adjustment unit 1042 is connected to the output terminal of the amplification unit 1041, the second terminal of the gain adjustment unit 1042 is connected to the second input terminal of the amplification unit 1041, and the third terminal of the gain adjustment unit 1042 is grounded. The amplification unit 1041 is used to amplify the feedback voltage VFB; the gain adjustment unit 1042 is used to determine the amplification factor of the feedback voltage VFB. Therefore, by combining the amplification unit 1041 and the gain adjustment unit 1042, the feedback voltage can be amplified by a preset factor, improving flexibility.

[0102] In other examples, the feedback module 104 may also include a programmable gain amplifier integrated circuit, which is a separate chip that receives gain codes sent by the user through a digital interface. The control logic inside the chip automatically switches the internal feedback resistor network to set the amplification factor to the corresponding value and realize the amplification function.

[0103] Optionally, the amplification unit 1041 includes a first operational amplifier. The non-inverting input terminal of the first operational amplifier serves as the first input terminal of the amplification unit 1041, the inverting input terminal serves as the second input terminal of the amplification unit 1041, and the output terminal serves as the output terminal of the amplification unit 1041. The first operational amplifier can perform amplification function, and a gain adjustment unit 1042 is provided between the inverting input terminal and the output terminal of the first operational amplifier. Then, the first operational amplifier can amplify the feedback voltage to a preset factor based on the amplification factor determined by the gain adjustment unit 1042.

[0104] In other examples, the amplification unit 1041 can also be implemented by means of discrete component construction, modular combination, or replacement with special function chips.

[0105] Optional, such as Figure 4 As shown, the gain adjustment unit 1042 includes a first resistor R1 and a second resistor R2. The first resistor R1 is connected between the inverting input terminal and the output terminal of the first operational amplifier; the second resistor R2 is connected between the inverting input terminal and the ground terminal of the first operational amplifier. That is, the first end of the first resistor serves as the first terminal of the gain adjustment unit 1042, the second end of the first resistor R1 is connected to the first end of the second resistor R2 and serves as the second terminal of the gain adjustment unit 1042, and the second end of the second resistor R2 serves as the third terminal of the gain adjustment unit 1042, i.e., ground.

[0106] According to the characteristics of an ideal operational amplifier, a virtual open circuit means that the current flowing into the inverting input is zero. Therefore, the current flowing through the first resistor is equal to the current flowing through the second resistor, i.e., I0.R1 =I R2 Virtual short refers to the situation where the potentials of the inverting input and the non-inverting input are equal, and the non-inverting input is grounded. .

[0107] Accordingly, the current relationship expression is:

[0108]

[0109] exist At that time, the output voltage is:

[0110]

[0111] Accordingly, the magnification is:

[0112]

[0113] in, It is the voltage at the non-inverting input of the first operational amplifier; It is the voltage at the inverting input terminal of the first operational amplifier; It is the output voltage of the operational amplifier; That is the resistance value of the first resistor; It is the resistance value of the second resistor; the symbol indicates that the output signal is opposite to the input signal at the inverting input terminal.

[0114] Based on this, the amplification factor of the feedback voltage can be adjusted by using the first resistor and the second resistor.

[0115] For example, when the amplification unit 1041 includes a first operational amplifier, a first resistor R1 is connected between the inverting input terminal and the output terminal of the first operational amplifier, and a second resistor R2 is connected between the inverting input terminal and the ground terminal of the first operational amplifier.

[0116] For example, the first resistor and the second resistor can be a single resistor or a resistor string, where a resistor string refers to multiple resistors connected in series.

[0117] The inventors discovered through research that the first operational amplifier itself also has an offset voltage Vos2, at which point the output current is:

[0118]

[0119] Therefore, the offset voltage Vos2 of the first operational amplifier will also affect the accuracy of the output current.

[0120] Optional, such as Figure 3As shown, the constant current drive circuit 10 includes a modulation module 105, which is connected between the input and output terminals of the feedback module 104 and is used to suppress the offset voltage of the first operational amplifier.

[0121] For example, the offset voltage Vos2 of the first operational amplifier can be suppressed using either Correlated Double Sampling (CDS) or Chopper Stabilization. Correlated Double Sampling suppresses offset voltage by sampling the signal twice (one sample for noise / offset, and one sample for signal + noise / offset), using the correlation between the two samples to cancel out fixed offset and low-frequency noise. Chopper Stabilization shifts DC offset and low-frequency noise to a higher frequency band using high-frequency chopping (modulation), then restores the signal through demodulation and low-pass filtering, while simultaneously filtering out the shifted offset and noise.

[0122] For example, chopper cancellation technology can be used to suppress offset voltage. Chopper cancellation technology has the property of continuous time, which can completely eliminate DC offset and low-frequency noise while preserving the continuous time domain characteristics of the signal, avoiding the distortion and bandwidth loss caused by discrete sampling.

[0123] Optional, such as Figure 4 As shown, the modulation module includes an input chopper modulator 1051 and an output chopper modulator 1052. The input chopper modulator 1051 is connected between the input terminal of the feedback module 104 and the non-inverting input terminal of the first operational amplifier, and is used to modulate the feedback voltage input to the first operational amplifier. The output chopper modulator 1052 is connected between the output terminal of the first operational amplifier and the output terminal of the feedback module 104, and is used to demodulate the output voltage of the first operational amplifier to suppress the offset voltage Vos2 of the first operational amplifier.

[0124] The input chopper modulator 1051 modulates the low-frequency sampled signal (feedback voltage) onto a high-frequency carrier. When amplified by the first operational amplifier, the offset and noise of the first operational amplifier itself are not modulated and remain at a low frequency. The output chopper modulator 1052 shifts the useful signal back to DC, while simultaneously modulating the offset and noise of the first operational amplifier to a high frequency, allowing subsequent low-pass filtering (which can be a simple capacitor or the bandwidth of the feedback loop itself) to easily remove them. This makes the accuracy of the feedback voltage no longer limited by the operational amplifier's own manufacturing process variations and temperature drift.

[0125] The inventors discovered through research that Vos2 can be reduced to 0.01mV using chopping cancellation technology. Furthermore, assuming K=10, Vos1 can be reduced to 0.1mV; as K increases, Vos1 decreases further. In this case, Vref can be increased to over 200mV, or even 1V. Assuming Vin input is 1V, VFB is now 1 / K; assuming K is 10, VFB is only 100mV. This is equivalent to increasing the LSB of the 108 digital-to-analog converter without increasing the VFB voltage, which is equivalent to not increasing the output power, thus improving system efficiency.

[0126] For example, the modulation module 105 may also include a clock generator connected to the input chopper modulator 1051 and the output chopper modulator 1052, for providing a synchronized modulation clock signal to the input chopper modulator 1051 and the output chopper modulator 1052, ensuring synchronization of modulation and demodulation, and avoiding distortion or gain error during modulation-demodulation.

[0127] Optional, such as Figure 3 As shown, the constant current drive circuit also includes a transient enhancement module 106, which is connected to the control terminal of the switch module 101. The transient enhancement module 106 is used to output a first transient current at the moment the switch module 101 is turned on, that is, to provide a first transient current to the control terminal of the switch module 101, so as to accelerate the voltage rise of the control terminal of the switch module 101 and realize the rapid establishment of the channel.

[0128] And / or, the transient enhancement module 106 is used to draw a second transient current from the control terminal of the switch module 101 at the instant the switch module 101 is turned off, that is, to provide a discharge current to the control terminal of the switch module 101 to discharge the charge of the control terminal of the switch module 101, accelerate the voltage drop of the control terminal of the switch module 101, and realize the rapid turn-off of the circuit.

[0129] Optional, such as Figure 4 As shown, the transient enhancement module 106 includes a pull-up current source 1061 and a pull-down current source 1062. The output terminal I_Pull of the pull-up current source 1061 is connected to the control terminal of the switching module 101 to provide a first transient current. The input terminal I_Down of the pull-down current source 1062 is connected to the control terminal of the switching module 101 to extract a second transient current. This allows for rapid channel establishment and rapid circuit shutdown.

[0130] For example, the transient enhancement module 106 may be used only to enable rapid channel establishment or only to enable rapid circuit shutdown. Accordingly, the transient enhancement module 106 may include only a pull-up current source 1061 or a pull-down current source 1062.

[0131] In some examples, such as Figure 5 As shown, the pull-up current source 1061 includes a first P-type transistor P1, a second P-type transistor P2, a third P-type transistor P3, a first current mirror 1063, a fourth P-type transistor P4, and a first inverter IVN1.

[0132] The source of the first P-type transistor P1 is connected to the power supply terminal VDD, and the drain of the first P-type transistor P1 is connected to the output terminal I_Pull of the pull-up current source 1061 for outputting the first transient current. The gate of the second P-type transistor P2 receives the bias voltage Vbias, and the source of the second P-type transistor P2 is connected to the power supply terminal VDD. The gate and drain of the third P-type transistor P3 are connected and connected to the gate of the first P-type transistor, and the source of the third P-type transistor P3 is connected to the power supply terminal VDD. The first and second terminals of the first current mirror 1063 are connected to the drains of the second P-type transistor P2 and the third P-type transistor P3, respectively, and the third terminal of the first current mirror 1063 is connected to the ground terminal.

[0133] The source of the fourth P-type transistor P4 is connected to the drain of the first P-type transistor P1, and the drain of the fourth P-type transistor P4 is connected to the drain of the first P-type transistor P1; the input of the first inverter INV1 receives the PWM control signal, and the output of the first inverter INV1 is connected to the gate of the fourth P-type transistor P4.

[0134] The second P-type transistor P2, the third P-type transistor P3, and the first current source 1063 are used to control the first P-type transistor P1 to be in the on state; the fourth P-type transistor P4 and the first inverter INV1 are used to control the pull-up time so that the first P-type transistor P1 outputs the first transient current.

[0135] The power supply terminal is used to provide the power supply voltage, and the grounding terminal is used to provide the grounding voltage, with the power supply voltage being greater than the grounding voltage.

[0136] Under the bias voltage Vbias, the second P-type transistor P2 is in the conducting state, which pulls up the voltage at the first terminal of the first current mirror 1063. Through the replication effect of the first current mirror 1063, the voltage at the second terminal of the first current mirror 1063 is pulled down, thereby controlling the first P-type transistor P1 to be in the conducting state. When the voltage at the second terminal of the first current mirror 1063 is pulled down, the third P-type transistor P3 is in the conducting state, clamping the source voltage of the second P-type transistor P2, making the power supply provided by the second P-type transistor P2 more stable and accurate.

[0137] When the PWM control signal is high, the first inverter INV1 inverts the PWM control signal, outputting a low-level signal. This causes the fourth P-type transistor P4 to be turned on, allowing the first P-type transistor P1 to output the first transient current. Therefore, the fourth P-type transistor P4 can be used to control the pull-up timing, which is the moment the first transient current is output.

[0138] For example, the first current mirror 1063 may include two differential pairs, which are used to increase the output impedance, enhance current constantness, improve current replication accuracy, and reduce matching error.

[0139] The two differential pairs are referred to as the first-stage differential pair and the second-stage differential pair, respectively. The first-stage differential pair includes a first N-type transistor N1 and a second N-type transistor N2, and the second-stage differential pair includes a third N-type transistor N3 and a fourth N-type transistor N4. The gate and drain of the first N-type transistor N1 are connected, serving as the first terminal of the first current mirror 1063; the gate of the second N-type transistor N2 is connected to the gate of the first N-type transistor N1, and the drain of the second N-type transistor N2 serves as the second terminal of the first current mirror 1063; the gate and drain of the third N-type transistor N3 are connected and connected to the source of the first N-type transistor N1, and the source of the third N-type transistor N3 serves as the third terminal of the first current mirror 1063; the gate of the fourth N-type transistor N4 is connected to the gate of the third N-type transistor N3, the drain of the fourth N-type transistor N4 is connected to the source of the second N-type transistor N2, and the source of the fourth N-type transistor N4 is connected to the source of the third N-type transistor N3.

[0140] For example, by adjusting the duty cycle of the PWM control signal, the conduction level or switching state of the fourth P-type transistor P4 can be controlled.

[0141] Optional, such as Figure 6 As shown, the pull-down current source 1062 includes a fifth N-type transistor N5, a fifth P-type transistor P5, a sixth N-type transistor N6, a seventh N-type transistor N7, an eighth N-type transistor N8, and a second inverter INV2.

[0142] The drain of the fifth N-type transistor N5 is connected to the input of the pull-down current source 1062; the gate of the fifth N-type transistor N5 receives the bias voltage Vbias, and the source of the fifth P-type transistor P5 is connected to the power supply terminal VDD; the gate and drain of the sixth N-type transistor N6 are connected, and are also connected to the drain of the sixth P-type transistor P6; the gate and drain of the seventh N-type transistor N7 are connected, and are also connected to the source of the sixth N-type transistor N6, and the source of the seventh N-type transistor N7 is connected to the ground terminal; the drain of the eighth N-type transistor N8 is connected to the source of the fifth N-type transistor N5, and the source of the eighth N-type transistor N8 is connected to the ground terminal; the input of the second inverter INV2 receives the PWM control signal, and the output of the second inverter INV2 is connected to the gate of the eighth N-type transistor N8.

[0143] The fifth P-type transistor P5, the sixth N-type transistor N6, and the seventh N-type transistor N7 are used to control the fifth N-type transistor N5 to be in the on state; the eighth N-type transistor N8 and the second inverter INV2 are used to control the pull-down time.

[0144] Under the bias voltage Vbias, the fifth P-type transistor P5 is in the on state, which pulls up the gate voltages of the fifth N-type transistor N5 and the sixth N-type transistor N6, thereby controlling the fifth N-type transistor N5 and the sixth N-type transistor N6 to be in the on state. When the sixth N-type transistor N6 is in the on state, it pulls up the gate voltage of the seventh N-type transistor N7, causing the seventh N-type transistor N7 to be in the on state, thereby clamping the source voltage of the fifth P-type transistor P5, making the power supply provided by the fifth P-type transistor P5 more stable and accurate.

[0145] When the PWM control signal is low, the second inverter INV2 inverts the PWM control signal, outputting a high-level signal. This causes the eighth N-type transistor N8 to be turned on, allowing the second transient current to be discharged through the conduction path of the fifth N-type transistor N5 and the eighth N-type transistor N8. Therefore, the eighth N-type transistor N8 can control the pull-down timing, which is also the timing of discharging the second transient current.

[0146] For example, by adjusting the duty cycle of the PWM control signal, the conduction level or switching state of the sixth N-type transistor N6N10 can be controlled.

[0147] For example, a pull-up current source may also include other chips or circuits capable of outputting transient current; a pull-down current source may also include other chips or circuits capable of extracting transient current.

[0148] Optionally, the transient enhancement module 106 may also include a bias voltage generation unit connected to the gate of the second P-type transistor P2 and the gate of the fifth P-type transistor P5, for providing a bias voltage Vbias.

[0149] Optional, such as Figure 7 As shown, the bias voltage generating unit includes a sixth P-type transistor P6, a ninth N-type transistor N9, a tenth N-type transistor N10, a third current mirror 1064, a fourth current mirror 1065, and a third resistor R3.

[0150] The gate of the sixth P-type transistor P6 is connected to the ground terminal VSS, and the source of the sixth P-type transistor P6 is connected to the power supply terminal VDD; the gate of the ninth N-type transistor N9 is connected to the drain of the sixth P-type transistor P6, and the source of the ninth N-type transistor N9 is connected to the ground terminal VSS; the drain of the tenth N-type transistor N10 is connected to the drain of the sixth P-type transistor P6, and the source of the tenth N-type transistor N10 is connected to the ground terminal VSS.

[0151] The first terminal of the third current mirror 1064 is connected to the power supply terminal VDD, and the second terminal of the third current mirror 1064 is connected to the drain of the ninth N-type transistor N9 and the output terminal of the bias voltage generating unit. The first and second terminals of the fourth current mirror 1065 are connected to the second and third terminals of the third current mirror 1064, respectively. The second terminal of the fourth current mirror 1065 is also connected to the gate of the tenth N-type transistor N10, and the third terminal of the fourth current mirror 1065 is connected to the ground terminal VSS. The first terminal of the third resistor R3 is connected to the fourth terminal of the fourth current mirror 1065, and the second terminal of the third resistor R3 is connected to the ground terminal VSS.

[0152] The sixth P-type transistor P6, the ninth N-type transistor N9, and the tenth N-type transistor N10 are used to control the startup of the third current mirror 1064 and the fourth current mirror 1065; the third current mirror 1064, the fourth current mirror 1065, and the third resistor R3 are used to control the bias voltage.

[0153] The gate of the sixth P-type transistor P6 receives a ground voltage and is in a conducting state, thereby pulling up the gate voltage of the ninth N-type transistor N9, making the ninth N-type transistor N9 in a conducting state, and thus starting the third current mirror 1064. After the third current mirror 1064 is started, it controls the fourth current mirror 1065 to start. Due to the voltage difference of the third resistor R3, the third terminal of the third current mirror 1064 can output a bias voltage.

[0154] For example, the third current mirror 1064 includes a seventh P-type transistor P7 and an eighth P-type transistor P8; the source of the seventh P-type transistor P7 serves as the first terminal of the third current mirror 1064, and the gate and drain of the seventh P-type transistor P7 are connected and serve as the second terminal of the third current mirror 1064; the source of the eighth P-type transistor P8 is connected to the source of the seventh P-type transistor P7, and the drain of the eighth P-type transistor P8 serves as the third terminal of the third current mirror 1064.

[0155] The fourth current mirror 1065 includes an eleventh N-type transistor N11 and a twelfth N-type transistor N12; the drain of the eleventh N-type transistor N11 serves as the first terminal of the fourth current mirror 1065; the drain and gate of the twelfth N-type transistor N12 are connected, serving as the second terminal of the fourth current mirror 1065; the source of the twelfth N-type transistor N12 serves as the third terminal of the fourth current mirror 1065; and the source of the eleventh N-type transistor N11 serves as the fourth terminal of the fourth current mirror 1065.

[0156] For example, a first switch S1 can be provided between the output terminal of the operational amplifier module 103 and the control terminal of the switching module 101 to control whether the control terminal of the switching module 101 can receive output current. The control terminal of the first switch S1 can receive a PWM signal, and when the PWM signal is in the on state, the control terminal of the switching module 101 can receive output current. The first switch S1 can be a transistor, relay, etc.

[0157] For example, a second switch S2 can be provided between the control terminal and the ground terminal of the switch module 101. When the second switch S2 is in the on state, it can accelerate the discharge of charge at the control terminal of the switch module 101.

[0158] Optionally, the constant current drive circuit also includes a bandgap reference source 107 and a digital-to-analog converter 108. The input terminal of the digital-to-analog converter 108 is connected to the bandgap reference source 107, and the output terminal of the digital-to-analog converter 108 is connected to the non-inverting input terminal of the operational amplifier module 103. The bandgap reference source 107 is used to provide a reference voltage Vref. The digital-to-analog converter 108 converts the reference voltage Vref into an analog voltage Vin based on a digital control signal and outputs the analog voltage Vin to the non-inverting input terminal of the operational amplifier module 103.

[0159] The bandgap reference source 107 provides a stable reference voltage, unaffected by temperature or power supply fluctuations; the digital-to-analog converter 108 converts digital quantities into analog voltage Vin.

[0160] The constant current driving circuit provided in this application has been described in detail above. This application also provides a driver that includes the constant current driving circuit described above.

[0161] For example, the driver may include a backlight driver.

[0162] This application also provides a display device, including a driver.

[0163] For example, the display device includes a backlight unit, which includes a backlight driver and a light-emitting module. The backlight driver is used to control the light-emitting state or light-emitting brightness of the light-emitting module by adjusting the output current of the light-emitting driver.

[0164] For example, the light-emitting module may include one or more LEDs.

[0165] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A constant current drive circuit, characterized in that, include: A switch module, the first end of which is connected to a light-emitting module and used to control the light-emitting state of the light-emitting module; A sampling module, wherein the first end of the sampling module is connected to the second end of the switching module and the second end of the sampling module is grounded, is used to determine the feedback voltage of the branch corresponding to the light-emitting module when the switching module is in the on state; An operational amplifier module is provided, wherein the non-inverting input terminal of the operational amplifier module receives an analog voltage, and the output terminal of the operational amplifier module is connected to the control terminal of the switching module for controlling the switching state of the switching module. The feedback module has its input terminal connected to the first terminal of the sampling module and its output terminal connected to the inverting input terminal of the operational amplifier module. It is used to amplify the feedback voltage so as to reduce the influence of the offset voltage of the operational amplifier module on the output current of the light-emitting drive when the analog voltage is the amplified voltage.

2. The constant current drive circuit according to claim 1, characterized in that, The feedback module includes: An amplification unit is provided, wherein the first input terminal of the amplification unit is connected to the input terminal of the feedback module, and the output terminal of the amplification unit is connected to the output terminal of the feedback module, for amplifying the feedback voltage; A gain adjustment unit is provided, with its first end connected to the output end of the amplification module and its second end connected to the second input end of the amplification module, for determining the amplification factor of the feedback voltage.

3. The constant current drive circuit according to claim 2, characterized in that, The amplification unit includes: A first operational amplifier, wherein the non-inverting input terminal of the first operational amplifier serves as the first input terminal of the amplification unit, the inverting input terminal of the first operational amplifier serves as the second input terminal of the amplification unit, and the output terminal of the first operational amplifier serves as the output terminal of the amplification unit; The gain adjustment unit includes: The first resistor is connected between the inverting input terminal and the output terminal of the first operational amplifier. The second resistor is connected between the inverting input of the first operational amplifier and ground.

4. The constant current drive circuit according to claim 3, characterized in that, Also includes: A modulation module, connected between the input and output terminals of the feedback module, is used to suppress the offset voltage of the first operational amplifier.

5. The constant current drive circuit according to claim 4, characterized in that, The modulation module includes: An input chopper modulator is connected between the input terminal of the feedback module and the non-inverting input terminal of the first operational amplifier, and is used to modulate the feedback voltage input to the first operational amplifier. An output chopper modulator is connected between the output terminal of the first operational amplifier and the output terminal of the feedback module to demodulate the output voltage of the first operational amplifier in order to suppress the offset voltage of the first operational amplifier.

6. The constant current drive circuit according to any one of claims 1-5, characterized in that, Also includes: The transient enhancement module is connected to the control terminal of the switching module; The transient enhancement module is used to provide a first transient current to the control terminal of the switch module at the moment the switch module is turned on, so as to accelerate the voltage rise of the control terminal of the switch module. And / or, to draw a second transient current from the control terminal of the switch module at the instant the switch module is turned off, so as to accelerate the voltage drop at the control terminal of the switch module.

7. The constant current drive circuit according to claim 6, characterized in that, The transient enhancement module includes: A pull-up current source, the output terminal of which is connected to the control terminal of the switching module, is used to provide the first transient current; A pull-down current source, the input terminal of which is connected to the control terminal of the switching module, is used to extract the second transient current.

8. The constant current drive circuit according to any one of claims 1-5, characterized in that, Also includes: A bandgap reference source is used to provide a reference voltage; A digital-to-analog converter, connected to the output of the bandgap reference source and the non-inverting input of the operational amplifier module, is used to output the analog voltage based on the reference voltage and the digital control signal.

9. A driver, characterized in that, The constant current drive circuit includes any one of claims 1-8.

10. A display device, characterized in that, Includes the driver as described in claim 9.

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