Current mirror circuit and LED driving circuit

Abstract

This application provides a current mirror circuit and an LED driver circuit. The current mirror circuit includes an input transistor, a replica transistor, and a control unit. The input transistor and the replica transistor are connected, with a reference current input through the input transistor and an output current output from the replica transistor. The control unit is connected between the input transistor and the replica transistor. By adjusting the series resistance values ​​of the input transistor and the replica transistor respectively, the accuracy of the replication ratio is ensured, thereby ensuring the accuracy of the output current of the replica transistor.

Description

Technical Field

[0001] This application relates to the field of current mirror technology, and more specifically, to a current mirror circuit and an LED driver circuit. Background Technology

[0002] In integrated circuit design, current mirrors are common basic circuits. Their function is to replicate the input current into the output current according to a certain ratio. However, due to changes in the operating state of the components used for replication, the replication ratio may shift, resulting in inaccurate current replication.

[0003] To address the aforementioned issues, existing technologies employ a method of connecting different numbers of devices separately. However, this approach suffers from problems such as discontinuous current flow and poor improvement. Utility Model Content

[0004] In view of this, the purpose of this application is to provide a current mirror circuit and an LED driver circuit to overcome the problems in the prior art.

[0005] In a first aspect, embodiments of this application provide a current mirror circuit, the current mirror circuit comprising: an input transistor, a replication transistor, and a control unit; the control unit is connected between the input transistor and the replication transistor; The input transistor is used to receive the reference current; The control unit is used to stabilize the replication ratio by adjusting the series resistance of the input tube and the replication tube respectively. The replication tube outputs replication current according to the replication ratio.

[0006] In some technical solutions of this application, the aforementioned control unit is used to detect the reference current, and when the reference current changes, adjust the first series resistance of the input tube and the second series resistance of the replica tube.

[0007] In some technical solutions of this application, the aforementioned control unit includes: a detection module, a first adjustable resistor, and a second adjustable resistor; The detection module is used to detect the reference current; The first adjustable resistor is used to adjust the value of the first series resistance; The second adjustable resistor is used to adjust the second series resistance value.

[0008] In some technical solutions of this application, the above-mentioned detection module is used to receive a reference voltage and a preset voltage threshold, and output a target signal; wherein, the target signal is used to adjust the series resistance of the input tube and the replication tube; The input transistor is used to receive the reference current and output the reference voltage; The replicating tube is used to receive the reference voltage.

[0009] In some technical solutions of this application, the target signal is a target voltage, and the detection module is used to output a low level of the target voltage when the reference voltage is greater than the voltage threshold. When the reference voltage is less than the voltage threshold, the target voltage is output at a high level.

[0010] In some technical solutions of this application, the target signal is a target voltage. The target voltage changes the voltage drop of the first adjustable resistor and the second adjustable resistor, thereby adjusting the series resistance of the input tube and the replica tube respectively. The first adjustable resistor is connected in series with the input tube, and the second adjustable resistor is connected in series with the replica tube.

[0011] In some technical solutions of this application, the above-mentioned detection module includes: an operational amplifier.

[0012] In some technical solutions of this application, the first adjustable resistor and the second adjustable resistor both include MOSFETs, transistors, or JFETs.

[0013] In some technical solutions of this application, both the input tube and the replication tube mentioned above include MOS transistors or triodes.

[0014] Secondly, embodiments of this application provide an LED driving circuit, including an LED and the aforementioned current mirror circuit.

[0015] The technical solutions provided by the embodiments of this application may include the following beneficial effects: The current mirror circuit in this application includes an input transistor, a replica transistor, and a control unit. The input transistor and the replica transistor are connected, with a reference current input through the input transistor and an output current output through the replica transistor. The control unit is connected between the input transistor and the replica transistor, and by adjusting the series resistance values ​​of the input transistor and the replica transistor respectively, the accuracy of the replication ratio is ensured, thereby ensuring the accuracy of the output current of the replica transistor.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the first current mirror circuit provided in an embodiment of this application is shown; Figure 2 A schematic diagram of a current mirror in the first prior art provided by an embodiment of this application is shown; Figure 3 A schematic diagram of a current mirror in the second prior art provided in this application embodiment is shown; Figure 4 A schematic diagram of the second current mirror circuit provided in an embodiment of this application is shown; Figure 5 A schematic diagram of the third current mirror circuit provided in an embodiment of this application is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0020] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0022] In integrated circuit design, current mirrors are common basic circuits. Their function is to replicate the input current to the output current at a certain ratio. The device used for replication can be a MOSFET or a transistor. The operating states of the devices may also differ; MOSFETs may operate in the saturation region, linear region, or even subthreshold region, while transistors may operate in the amplification region or saturation region. In some applications, such as LED backlighting or automotive taillight drivers, multi-channel MOS current sources (or current sinks) are used to light LED strings. The output current is often obtained by replicating the input reference current using a current mirror, and its range is very wide, such as 5mA to 100mA. This twenty-fold operating range causes significant variations in the operating state of the replicating MOS; at high currents, the MOS operates in the linear region, at medium currents in the saturation region, and at low currents even in the subthreshold region. A 1:N NMOS current mirror is shown below. Figure 2 As shown, Iin is the input reference current, M4 is obtained by N M3 connected in parallel, and ideally Iout = N * Iin.

[0023] In reality, due to random differences in Vth (threshold voltage, the minimum gate-source voltage required to transition from "off state" to "on state"), W / L (width-to-length ratio, where W refers to the width of the MOSFET's conductive channel and L refers to the length of the conductive channel), and K (conductivity parameter, k=μ*Cox, where μ is the electron mobility and Cox is the gate oxide capacitance per unit area) between M3 and M4, the ideal replication ratio of N will be offset (hereinafter referred to as mismatch).

[0024] Existing solutions such as Figure 3As shown, M3a, M3b, M4a, and M4b with Sa and Sb control are added. M4a / M3a = M4b / M3b = M4 / M3 = N, and M3b / M3a = M4b / M4a > 1. When Sa is high, M3a and M4a are connected to M3 and M4 respectively, otherwise they are disconnected. When Sb is high, M3b and M4b are connected to M3 and M4 respectively, otherwise they are disconnected. The current gear judgment and logic module detect Iin and divide Iin into four gears according to three thresholds (Ihigh, Imid, Ilow, Ihigh > Imid > Ilow). When Iin > Ihigh, both Sa and Sb are high, and all the tubes are connected; when Imid < Iin < Ihigh, Sa is low and Sb is high, and M3b and M4b are connected; when Ilow < Iin < Imid, Sa is high and Sb is low, and M3a and M4a are connected; when Iin < Ilow, both Sa and Sb are low, and none of the four tubes are connected. The smaller Iin is, the fewer the number of MOS tubes connected, that is, the smaller W / L is. Observing the formula of Ids (output current), regardless of the magnitude of Ids, the trend that Vgs - Vth decreases as Ids decreases is suppressed (Vgs is the gate-source voltage). When designed reasonably, the MOS does not enter the subthreshold region or the saturation region with a small Vgs - Vth, so the mismatch at small currents is suppressed.

[0025] The problems existing in the existing solutions are as follows: when Iout is small, the number of connected tubes decreases, and the matching effect of the layout becomes worse, resulting in a worse improvement effect of small-current mismatch. When Iin is divided into several gears, when Iin continuously changes and crosses the threshold point, Sa and Sb jump, bringing jump glitches and discontinuities to Iout.

[0026] Based on this, the embodiments of the present application provide a current mirror circuit. Some embodiments of the present application will be described in detail below. Without conflict, the embodiments described below and the features in the embodiments can be combined with each other.

[0027] Figure 1 The flow schematic diagram of the current mirror circuit provided by the embodiments of the present application is shown. The current mirror circuit in the embodiments of the present application includes an input tube 101, a replication tube 102, and a regulation unit 103. The input tube 101 is connected to the replication tube 102. The reference current is input from the input tube 101, and the output current is obtained by outputting from the replication tube 102. The regulation unit 103 is connected between the input tube 101 and the replication tube 102. By adjusting the series resistances of the input tube 101 and the replication tube 102 respectively, the accuracy of the replication ratio is ensured, and further the accuracy of the output current of the replication tube 102 is ensured.

[0028] In an optional implementation, the input transistor 101 and the replication transistor 102 in this embodiment include MOSFETs or transistors. For example, the input transistor 101 is a first MOSFET (M1), and the replication transistor 102 is a second MOSFET (M2). Alternatively, the input transistor 101 is a first transistor (M5), and the replication transistor 102 is a second transistor (M6). That is, the current mirror circuit in this embodiment can only be constructed using MOSFETs or transistors, and is not applicable to current mirror circuits constructed using other forms (such as resistors).

[0029] In an optional implementation, when the control unit 103 adjusts the series resistance of the input transistor 101 and the replica transistor 102, the adjustment is based on the reference current of the input transistor 101. That is, the control unit 103 in this embodiment needs to detect the reference current received by the input transistor 101. The detection of the reference current mainly determines whether the reference current has changed. Only when the reference current changes will the control unit 103 in this embodiment adjust the first series resistance value of the input transistor and the second series resistance value of the replica transistor.

[0030] In practice, the method for determining whether the reference current has changed is to set a current threshold. If the detected reference current exceeds this current threshold, it is considered that the reference current has changed. It should be noted that the current threshold can be a single value or two values ​​(an upper limit and a lower limit). The specific data and number of current thresholds can be determined according to the specific circuit and / or service requirements.

[0031] In an alternative implementation, such as Figure 4 The control unit 103 in this embodiment includes a first adjustable resistor and a second adjustable resistor. The first adjustable resistor is connected in series with the input transistor 101, and the second adjustable resistor is connected in series with the replication transistor 102. That is, this embodiment changes the first series resistance of the input transistor 101 by changing the value of the first adjustable resistor, and changes the second series resistance of the replication transistor 102 by changing the value of the second adjustable resistor. In specific implementations, the first and second adjustable resistors can be MOSFETs, transistors, or JFETs, etc. When setting the resistors, if the replication ratio of the input transistor 101 to the replication transistor 102 is 1:N, then the resistance ratio of the first adjustable resistor to the second adjustable resistor is N:1.

[0032] In this embodiment, the control unit 103 further includes a detection module. The detection module detects the reference current and, when it determines that the reference current has changed, increases or decreases the first adjustable resistor and the second adjustable resistor, thereby changing the first series resistance value of the input tube 101 and the second series resistance value of the replication tube 102.

[0033] In an optional implementation, when the input transistor 101 is a MOSFET or a transistor, it receives a reference current and outputs a reference voltage. The replication transistor 102 receives the reference voltage output by the input transistor 101 and outputs a replication current. The multiple replication currents are integrated to obtain the output current. Since the input transistor 101 outputs a reference voltage and its own resistance remains unchanged, the detection module's detection of the reference current in the above embodiment can be converted into the detection of the reference voltage. The current threshold in the above embodiment can be converted into the corresponding voltage threshold. The setting process of the voltage threshold is the same as that of the current threshold, and will not be described again here. That is to say, the input of the detection module in this embodiment includes the reference voltage and the voltage threshold. By comparing the reference voltage and the voltage threshold, a target signal is output, and the target signal can adjust the resistance values ​​of the first adjustable resistor and the second adjustable resistor.

[0034] The resistance values ​​of the first and second adjustable resistors can be adjusted by changing their input voltages. That is, the target signal output by the adjustment module can be a target voltage. In this embodiment, the resistance values ​​of the first and second adjustable resistors are adjusted by changing their input voltages, or the target voltage changes the voltage drop across the first and second adjustable resistors, thereby adjusting the first series resistance of the input transistor 101 and the second series resistance of the replica transistor 102, respectively.

[0035] In practical implementation, the detection module here can be an operational amplifier (the operation mode of the operational amplifier is the existing technology and will not be described in detail here). The first input terminal of the operational amplifier is input to a reference voltage, and the second input terminal is input to a voltage threshold. When the reference voltage is greater than the voltage threshold, the target voltage is output at a low level; when the reference voltage is less than the voltage threshold, the target voltage is output at a high level.

[0036] In an optional implementation, the current mirror circuit in the embodiments of this application can be configured according to... Figure 5 Connect the components as shown. The positive terminal of the operational amplifier (OPA) is connected to the common gate of M1 and M2, and the negative terminal is connected to a suitable reference voltage (voltage threshold) VREF. The output of the OPA is connected to the common gate of MOSFETs M1S and M2S. M1S is equivalent to a variable resistor R (first adjustable resistor). M2S is obtained by connecting N NMOS transistors of the same size as M1S in parallel, and is equivalent to a variable resistor R / N (second adjustable resistor).

[0037] Because of the random differences in Vth, W / L, and K between M1 and M2, the ideal replication ratio of N is offset. When the gate-source voltage Vgs is greater than Vth, the MOSFET begins to form a conductive channel, allowing current to flow; if Vgs is less than Vth, the MOSFET is approximately cut off. The random difference in Vth between M1 and M2 is the "main source of error" causing current mirror mismatch, and as the current decreases (MOSFET operating state switching), the impact of Vth mismatch on output current mismatch is significantly aggravated. The derivation of current mirror mismatch under different operating states of the MOSFET is as follows: Ids and mismatch of MOSFET operating in the linear region:

[0038]

[0039] Ids and mismatch of MOSFET operating in the saturation region:

[0040]

[0041] Ids and mismatch of MOSFET operating in the subthreshold region:

[0042]

[0043] When the MOSFET is in the linear region We can obtain:

[0044] Therefore, compared to the linear region, the current mismatch in the saturation region is more sensitive to the mismatch with Vth; compared to the subthreshold region and the saturation region:

[0045] In other words, compared to the saturation region, the current mismatch in the subthreshold region is more sensitive to the Vth mismatch. We can conclude that as the current decreases and the MOS operating state changes, the contribution of the Vth mismatch to the Ids mismatch becomes increasingly significant. The accuracy degradation trend is obvious at low currents, and a twenty-fold increase in operating range can lead to a several-fold increase in current mismatch. Therefore, it is advisable to avoid entering the subthreshold region and the saturation region where Vgs-Vth are relatively small.

[0046] The control unit detects Iin and controls the resistance value. When Iin is large, R is very small and the voltage drop is very small. To simplify the calculation, the voltage drop of R is ignored. The circuit state is equivalent to the linear region or the saturation region with a large Vgs-Vth. Its mismatch (the mismatch between the output current and the reference current) is as follows: Output current (Ids):

[0047]

[0048] While maintaining a small mismatch, the voltage margin consumed is very small.

[0049] When the current is small, R increases, and its voltage drop becomes significant. The current mismatch is:

[0050] If Ids*R is large enough, the current mismatch can be very small.

[0051] In an optional implementation, this application also provides an LED driving circuit, including an LED and the current mirror circuit of any of the above embodiments.

[0052] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In addition, the terms "first", "second", "third", etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0053] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application. All should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A current mirror circuit, characterized in that, The current mirror circuit includes: an input transistor, a replication transistor, and a control unit; the control unit is connected between the input transistor and the replication transistor. The input transistor is used to receive the reference current; The control unit is used to stabilize the replication ratio by adjusting the series resistance of the input tube and the replication tube respectively. The replication tube outputs replication current according to the replication ratio.

2. The current mirror circuit according to claim 1, characterized in that, The control unit is used to detect the reference current, and when the reference current changes, adjust the first series resistance of the input tube and the second series resistance of the replica tube.

3. The current mirror circuit according to claim 2, characterized in that, The control unit includes: a detection module, a first adjustable resistor, and a second adjustable resistor; The detection module is used to detect the reference current; The first adjustable resistor is used to adjust the value of the first series resistance; The second adjustable resistor is used to adjust the second series resistance value.

4. The current mirror circuit according to claim 3, characterized in that, The detection module is used to receive a reference voltage and a preset voltage threshold, and output a target signal; wherein, the target signal is used to adjust the series resistance of the input tube and the replication tube; The input transistor is used to receive the reference current and output the reference voltage; The replicating tube is used to receive the reference voltage.

5. The current mirror circuit according to claim 4, characterized in that, The target signal is the target voltage; The detection module is used to output a low-level target voltage when the reference voltage is greater than the voltage threshold. When the reference voltage is less than the voltage threshold, a high-level target voltage is output.

6. The current mirror circuit according to claim 4, characterized in that, The target signal is the target voltage; The target voltage changes the voltage drop across the first adjustable resistor and the second adjustable resistor, thereby adjusting the series resistance of the input transistor and the replica transistor respectively; wherein, the first adjustable resistor is connected in series with the input transistor, and the second adjustable resistor is connected in series with the replica transistor.

7. The current mirror circuit according to claim 3, characterized in that, The detection module includes an operational amplifier.

8. The current mirror circuit according to claim 3, characterized in that, Both the first adjustable resistor and the second adjustable resistor include a MOSFET, a bipolar transistor, or a JFET.

9. The current mirror circuit according to claim 1, characterized in that, Both the input transistor and the replication transistor include MOSFETs or bipolar transistors.

10. An LED driving circuit, characterized in that, Includes LEDs and the current mirror circuit as described in any one of claims 1 to 9.

Images