Bandgap reference circuit

Abstract

The present invention provides a bandgap reference circuit, comprising: three branches, each branch comprising a current source connected in series between a power supply terminal and a ground terminal and a triode connected in the form of a diode, wherein the anodes of the diode formed by the three triodes provide a first voltage, a second voltage, and a third voltage, respectively; an operational amplifier comprising a first input terminal, a second input terminal, and an output terminal; a switch assembly comprising a plurality of switches for periodically controlling the on / off state of each switch; an integrating capacitor coupled between the first input terminal and the output terminal of the operational amplifier; a first sampling capacitor and a second sampling capacitor, wherein in a first phase of each switching cycle, the switch assembly is controlled so that the first sampling capacitor samples the voltage difference between the first voltage and the second voltage and the second sampling capacitor samples the third voltage, and in a second phase of each switching cycle, the switch assembly is controlled so that the charge collected by the first sampling capacitor and the second sampling capacitor is transferred to the integrating capacitor.

Description

Technical field

[0001] The present invention relates to the field of analog circuits, and in particular to a bandgap reference circuit. [Background Technology]

[0002] For a power supply to output a precise voltage, it needs a precise reference point, which is usually the reference voltage. Among commonly used reference voltage circuits, the bandgap reference source is a common and accurate reference source.

[0003] A bandgap reference, also known as an energy gap reference power supply, refers to the energy difference between the lowest point in the conduction band and the highest point in the valence band of a semiconductor or insulator. Bandgap references offer excellent temperature stability and are often used for high-precision voltage references. The principle is to incorporate components or subcircuits with both positive and negative temperature coefficients in a circuit. By properly arranging these components or subcircuits so that temperature variations cancel each other out, a constant value that is essentially independent of temperature can be obtained.

[0004] Figure 1 This is a circuit diagram of a traditional bandgap reference circuit (or bandgap reference source). The bandgap reference circuit includes two transistors Q1 and Q2, three resistors R1, R2 and R3, and an operational amplifier A1. The specific connection relationship is as follows: Figure 1 , which will not be repeated here. The output voltage Vout of the bandgap reference circuit is expressed as:

[0005] Vout=VBE2+(VBE1-VBE2)·R2 / R3,

[0006] Wherein, VBEk (k=1, 2, 3) is a function of temperature T, VBE1 is the base-emitter voltage of transistor Q1, and VBE2 is the base-emitter voltage of transistor Q2.

[0007] VBE1=V T ln(I1 / I s1 ), VBE2=V T ln(I2 / I s2 ),

[0008] Where I1 is the current of the branch where transistor Q1 is located, I2 is the current of the branch where transistor Q2 is located, I1=I2, I s2 =nI s1 , n>1, the saturation current of the PN junction of transistor Q1 is I s1 , the saturation current of the PN junction of transistor Q2 is I s2 , n is the size ratio of transistors Q1 and Q2.

[0009] Replace VBE1 and VBE2 with functions of temperature T, and the expression of Vout for temperature T is:

[0010] Vout = V T ln(I2 / I s2 )+V T ln(n)(1+R2 / R3)

[0011] Where V T is a constant, I s2 and n are the device characteristics of Q1 and Q2, which can be set manually. T ln(I2 / I s2 ) with respect to temperature is a negative number, and V T The partial derivative of ln(n)(1+R2 / R3) with respect to temperature is a positive number. By selecting appropriate values ​​for resistors R2 and R3, the partial derivative of Vout with respect to temperature can be made zero, meaning it remains unchanged with temperature. This makes the output voltage of the bandgap reference circuit independent of temperature.

[0012] However, this bandgap reference circuit has the following disadvantages: 1) transistors Q1 and Q2 must be turned on all the time, consuming extra energy; 2) an additional startup circuit is required, otherwise the circuit will not work; 3) the output voltage Vout can only be equal to the bandgap reference voltage Vg.

[0013] Therefore, it is urgent to propose a new technical solution to solve the above problems. [Summary of the invention]

[0014] One of the objectives of the present invention is to provide a bandgap reference circuit, which does not require an additional startup circuit and can set the voltage value of the output voltage Vout as needed.

[0015] To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a bandgap reference circuit, comprising: a first branch, comprising a first current source connected in series between a power supply terminal and a ground terminal and a first transistor connected in the form of a diode, wherein the anode of the diode formed by the first transistor provides a first voltage; a second branch, comprising a second current source connected in series between the power supply terminal and the ground terminal and a second transistor connected in the form of a diode, wherein the anode of the diode formed by the second transistor provides a second voltage; a third branch, comprising a third current source connected in series between the power supply terminal and the ground terminal and a third transistor connected in the form of a diode, wherein the diode formed by the third transistor provides a second voltage. The anode of the tube provides a third voltage; an operational amplifier, which includes a first input terminal, a second input terminal and an output terminal; a switch combination, which includes a plurality of switches, and periodically controls the conduction or disconnection of each switch; an integrating capacitor, which is coupled between the first input terminal and the output terminal of the operational amplifier; a first sampling capacitor and a second sampling capacitor, in the first phase of each switching cycle, the switch combination is controlled so that the first sampling capacitor samples the voltage difference between the first voltage and the second voltage, and the second sampling capacitor samples the third voltage, and in the second phase of each switching cycle, the switch combination is controlled to transfer the charge collected by the first sampling capacitor and the second sampling capacitor to the integrating capacitor.

[0016] Furthermore, the switch combination includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The first switch is coupled between the first voltage and the first terminal of the first sampling capacitor, the second switch is coupled between the second terminal of the first sampling capacitor and the second voltage, the third switch is coupled between the first terminal of the first sampling capacitor and the ground terminal, the fourth switch is coupled between the second terminal of the first sampling capacitor and the first input terminal of the operational amplifier, the fifth switch is coupled between the third voltage and the first terminal of the second sampling capacitor, the sixth switch is coupled between the second terminal of the second sampling capacitor and the ground terminal, the seventh switch is coupled between the first terminal of the second sampling capacitor and the ground terminal, and the eighth switch is coupled between the second terminal of the second sampling capacitor and the first input terminal of the operational amplifier. In a first phase of each switching cycle, the first, second, fifth, and sixth switches are turned on, and the third, fourth, seventh, and eighth switches are turned off. In a second phase of each switching cycle, the first, second, fifth, and sixth switches are turned off, and the third, fourth, seventh, and eighth switches are turned on. The second input terminal of the operational amplifier is coupled to the ground terminal.

[0017] Furthermore, the on or off of the first switch, the second switch, the fifth switch and the sixth switch is controlled by the first control signal CK1, and the on or off of the third switch, the fourth switch, the seventh switch and the eighth switch is controlled by the second control signal CK2. The timing of the first control signal CK1 and the second control signal CK2 is non-overlapping and complementary.

[0018] Furthermore, each of the first branch, the second branch, and the third branch is connected in series with a branch switch. In the first phase of each switching cycle, the branch switch is controlled to be turned on so that the first transistor, the second transistor, and the third transistor are turned on. In the second phase of each switching cycle, the branch switch is controlled to be turned off so that the first transistor, the second transistor, and the third transistor are turned off.

[0019] Furthermore, the first voltage is the base-emitter voltage VBE1 of the first transistor, the second voltage is the base-emitter voltage VBE2 of the second transistor, and the third voltage is the base-emitter voltage VBE3 of the third transistor.

[0020] The output terminal of the operational amplifier outputs a reference voltage. The saturation current of the PN junction of the first transistor is I s1 , the saturation current of the PN junction of the second transistor is I s2 , the saturation current of the PN junction of the third transistor is I s3 , the current of the first current source is I1, the current of the second current source is I2, where I1=I2, I s2 =n*I s1 , n is a positive number greater than 1.

[0021] Compared with the prior art, the present invention has one or more of the following advantages: 1) no additional startup circuit is required, saving circuit area; 2) the output voltage Vout can be a value other than the bandgap reference voltage Vg, which is more flexible and convenient; 3) the transistors Q1, Q2 and Q3 can be temporarily turned off, saving energy consumption.

Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0023] Figure 1 This is a circuit diagram of a traditional bandgap reference circuit;

[0024] Figure 2 is a circuit structure diagram of a bandgap reference circuit in one embodiment of the present invention;

[0025] Figure 3 for Figure 2 Timing diagram of the control signals of the switch combination of the bandgap reference circuit. [Specific implementation method]

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to separate or selective embodiments that are mutually exclusive of other embodiments. Unless otherwise specified, the terms "connected," "connected," and "connected" herein, indicating electrical connection, refer to direct or indirect electrical connection.

[0028] In the present invention, unless otherwise expressly specified or limited, terms such as "connected," "connected," and "coupled" should be understood broadly; for example, they may refer to direct connection or indirect connection through an intermediary, such as an electronic component or functional circuit. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0029] Figure 2 FIG. 1 is a circuit diagram of a bandgap reference circuit in one embodiment of the present invention. Figure 2 As shown, the bandgap reference circuit includes a first branch, a second branch and a third branch.

[0030] The first branch includes a first current source I1 connected in series between the power supply and the ground terminal, and a first transistor connected in diode form. The anode of the diode D1 formed by the first transistor provides a first voltage VBE1. The second branch includes a second current source I2 connected in series between the power supply and the ground terminal, and a second transistor connected in diode form. The anode of the diode D2 formed by the second transistor provides a second voltage VBE2. The third branch includes a third current source I3 connected in series between the power supply and the ground terminal, and a third transistor connected in diode form. The anode of the diode D3 formed by the third transistor provides a third voltage VBE3. The first voltage VBE1 is the base-emitter voltage of the first transistor, the second voltage VBE2 is the base-emitter voltage of the second transistor, and the third voltage VBE3 is the base-emitter voltage of the third transistor.

[0031] like Figure 1As shown, the connection method of transistors Q1 and Q2 is that the transistors Q1 and Q2 are connected in the form of diodes. The transistors Q1 and Q2 are NPN transistors, and their bases and collectors are coupled. In the present invention, each transistor can be an NPN transistor, and after its base and collector are coupled, it serves as the anode of the diode coupled to the output end of the current source, the input end of the current source is coupled to the power supply end, and its emitter serves as the cathode of the diode coupled to the ground end. Of course, in another embodiment, each transistor can be a PNP transistor, and after its base and collector are coupled, it serves as the cathode of the diode coupled to the ground end, and its emitter serves as the anode of the diode coupled to the output end of the current source.

[0032] like Figure 2 As shown, the bandgap reference circuit also includes an operational amplifier A, a switch combination, an integral capacitor C f , the first sampling capacitor C in1 and the second sampling capacitor C in2 The operational amplifier A includes a first input terminal, a second input terminal, and an output terminal. The second input terminal of the operational amplifier A is coupled to the ground terminal. The integral capacitor C f The switch combination includes a plurality of switches S1-S8, which periodically control the on or off of each switch. In the first stage of each switching cycle, the switch combination is controlled so that the first sampling capacitor C in1 The voltage difference (VBE1-VBE2) between the first voltage VBE1 and the second voltage VBE2 is sampled, and the second sampling capacitor C in2 Sampling the third voltage VBE3, in the second phase of each switching cycle, controlling the switch combination to connect the first sampling capacitor C in1 and the second sampling capacitor C in2 The collected charge is transferred to the integrating capacitor C f middle.

[0033] like Figure 2 As shown, the switch combination includes a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, a sixth switch S6, a seventh switch S7 and an eighth switch S8.

[0034] The first switch S1 is coupled to the first voltage VBE1 and the first sampling capacitor C in1 The second switch S2 is coupled to the first sampling capacitor C in1 The third switch S3 is coupled to the first sampling capacitor C in1 The fourth switch S4 is coupled between the first terminal and the ground terminal of the first sampling capacitor C in1 between the second end of and the first input terminal of operational amplifier A.

[0035] The fifth switch S5 is coupled to the third voltage VBE3 and the second sampling capacitor C in2 The sixth switch S6 is coupled to the first end of the second sampling capacitor C in2 The seventh switch S7 is coupled to the second sampling capacitor C in2 The eighth switch S8 is coupled between the first terminal and the ground terminal of the second sampling capacitor C in2 between the second end of and the first input terminal of operational amplifier A.

[0036] Each switching cycle is divided into two phases. In the first phase of each switching cycle, the first switch S1, the second switch S2, the fifth switch S5 and the sixth switch S6 are turned on, and the third switch S3, the fourth switch S4, the seventh switch S7 and the eighth switch S8 are turned off. At this time, the first sampling capacitor C in1 The voltage difference (VBE1-VBE2) between the first voltage VBE1 and the second voltage VBE2 is sampled, and the second sampling capacitor C in2 The third voltage VBE3 is sampled.

[0037] In the second phase of each switching cycle, the first switch S1, the second switch S2, the fifth switch S5 and the sixth switch S6 are turned off, and the third switch S3, the fourth switch S4, the seventh switch S7 and the eighth switch S8 are turned on. in1 and the second sampling capacitor C in2 The collected charge is transferred to the integrating capacitor C f The switching cycle is repeated periodically.

[0038] The first switch S1, the second switch S2, the fifth switch S5 and the sixth switch S6 are turned on or off by the first control signal CK1, and the third switch S3, the fourth switch S4, the seventh switch S7 and the eighth switch S8 are turned on or off by the second control signal CK2. Figure 3 As shown, the timing of the first control signal CK1 and the second control signal CK2 are non-overlapping and complementary, that is, the first switch S1 and the third switch S3 will not be turned on at the same time. There is a dead zone between the turning on of the first switch S1 and the turning on of the third switch S3, at which time the first switch S1 and the third switch S3 will be turned off at the same time.

[0039] At the end of each switching cycle, the output voltage Vout of the bandgap reference circuit is:

[0040] Vout=VBE3·C in2 / C f +(VBE1-VBE2)·C in1 / C f

[0041] Similarly, after replacing VBEk (k = 1, 2, 3) with the expression of temperature T, the expression of Vout with respect to T is:

[0042] Vout = V T ln(I3 / I s3 )·C in2 / C f +V T ln(n)·C in1 / C f

[0043] Where I1, I2, and I3 are the current values ​​of the first current source, the second current source, and the third current source respectively. The saturation current of the PN junction of the first transistor is I s1 , the saturation current of the PN junction of the second transistor is I s2 , the saturation current of the PN junction of the third transistor is I s3 In this embodiment, I1=I2, I s2 =n*I s1 , n is a positive number greater than 1. Similarly, V T ln(I3 / I s3 ) with respect to temperature is a negative number and V T The partial derivative of ln(n) with respect to temperature is positive, and by adjusting C in1 and C in2 The ratio of makes the partial derivative of the output voltage Vout with respect to temperature zero, that is, it does not change with temperature. In this way, the output voltage Vout is a constant that is independent of temperature.

[0044] In other embodiments, I1 may not be equal to I2. s2 and I s1 It can also be set as needed.

[0045] In one embodiment, to reduce power consumption, a branch switch is connected in series in each of the first, second, and third branches. During the first phase of each switching cycle, the branch switch is controlled to be turned on, thereby turning on the first, second, and third transistors. During the second phase of each switching cycle, the branch switch is controlled to be turned off, thereby turning off the first, second, and third transistors. This temporarily turns off the first, second, and third transistors, saving power.

[0046] The output voltage Vout can be set to a value other than the bandgap reference voltage Vg as needed, which is more flexible and convenient.

[0047] In addition, the bandgap reference circuit in the present invention does not require an additional startup circuit, which can save circuit area.

[0048] In the description of this specification, reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0049] Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention, and that those skilled in the art may make changes, modifications and variations to the above embodiments within the scope of the present invention.

Claims

1. A bandgap reference circuit, characterized in that: It includes: A first branch includes a first current source connected in series between a power supply terminal and a ground terminal and a first transistor connected in the form of a diode, wherein an anode of the diode formed by the first transistor provides a first voltage; a second branch comprising a second current source connected in series between the power supply terminal and the ground terminal and a second transistor connected in the form of a diode, wherein the anode of the diode formed by the second transistor provides a second voltage; a third branch comprising a third current source connected in series between the power supply terminal and the ground terminal and a third triode connected in the form of a diode, wherein an anode of the diode formed by the third triode provides a third voltage; an operational amplifier comprising a first input terminal, a second input terminal, and an output terminal; A switch combination, which includes multiple switches and periodically controls the on or off of each switch; an integrating capacitor coupled between the first input terminal and the output terminal of the operational amplifier; A first sampling capacitor and a second sampling capacitor are provided. In the first phase of each switching cycle, the switch combination is controlled so that the first sampling capacitor samples the voltage difference between the first voltage and the second voltage, and the second sampling capacitor samples the third voltage. In the second phase of each switching cycle, the switch combination is controlled to transfer the charge collected by the first sampling capacitor and the second sampling capacitor to the integration capacitor. The switch combination includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, a seventh switch and an eighth switch, The first switch is coupled between the first voltage and the first terminal of the first sampling capacitor, the second switch is coupled between the second terminal of the first sampling capacitor and the second voltage, the third switch is coupled between the first terminal of the first sampling capacitor and the ground terminal, and the fourth switch is coupled between the second terminal of the first sampling capacitor and the first input terminal of the operational amplifier. The fifth switch is coupled between the third voltage and the first terminal of the second sampling capacitor, the sixth switch is coupled between the second terminal of the second sampling capacitor and the ground terminal, the seventh switch is coupled between the first terminal of the second sampling capacitor and the ground terminal, and the eighth switch is coupled between the second terminal of the second sampling capacitor and the first input terminal of the operational amplifier. In the first phase of each switching cycle, the first switch, the second switch, the fifth switch, and the sixth switch are turned on, and the third switch, the fourth switch, the seventh switch, and the eighth switch are turned off. In the second phase of each switching cycle, the first switch, the second switch, the fifth switch, and the sixth switch are turned off, and the third switch, the fourth switch, the seventh switch, and the eighth switch are turned on. The second input terminal of the operational amplifier is coupled to the ground terminal.

2. The bandgap reference circuit according to claim 1, wherein: The on or off of the first switch, the second switch, the fifth switch and the sixth switch is controlled by the first control signal CK1, and the on or off of the third switch, the fourth switch, the seventh switch and the eighth switch is controlled by the second control signal CK2. The timing of the first control signal CK1 and the second control signal CK2 is non-overlapping and complementary.

3. The bandgap reference circuit according to claim 1, wherein: Each of the first branch, the second branch and the third branch is connected in series with a branch switch. In the first phase of each switching cycle, the branch switches are controlled to be turned on so that the first transistor, the second transistor and the third transistor are turned on. In the second phase of each switching cycle, the branch switches are controlled to be turned off, so that the first transistor, the second transistor and the third transistor are turned off.

4. The bandgap reference circuit according to claim 1, wherein: The first voltage is the base-emitter voltage VBE1 of the first transistor, the second voltage is the base-emitter voltage VBE2 of the second transistor, and the third voltage is the base-emitter voltage VBE3 of the third transistor. The output voltage outputted from the output terminal of the operational amplifier is a voltage that does not change with temperature.

5. The bandgap reference circuit according to claim 1, wherein: The saturation current of the PN junction of the first transistor is I s1 , the saturation current of the PN junction of the second transistor is I s2 , the saturation current of the PN junction of the third transistor is I s3 , the current of the first current source is I1, the current of the second current source is I2, where I1=I2, I s2 =n*I s1 , n is a positive number greater than 1.

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