Constant voltage generation circuit

Abstract

To provide a constant voltage generation circuit capable of providing a current capability.SOLUTION: A constant voltage generating circuit (11) includes: a first transistor (M1) configured as a depletion-type N-channel MOSFET and having a first drain connected to an application terminal of an input voltage (Vin), a first source, and a first gate shorted to the first source; a second transistor (M2) configured as an N-channel MOSFET and having a second drain connected to the first source, a second source, and a second gate; a third transistor (M3) configured as an N-channel MOSFET and having a third drain connected to the first drain, a third gate connected to the first source, and a third source connected to the second gate; and an output terminal (Tout) connected to the second gate and configured to output an output voltage (Vout).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a constant voltage generating circuit. [Background technology]

[0002] Conventionally, as one type of constant-voltage generating circuit, an ED type constant-voltage source that combines a depletion-type N-channel metal oxide semiconductor field effect transistor (MOSFET) and an enhancement-type N-channel MOSFET is widely known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 172001

[0004] [overview] In this case, in consideration of the load connected to the constant voltage generating circuit, the constant voltage generating circuit is sometimes required to have a certain current capability.

[0005] In view of the above circumstances, an object of the present disclosure is to provide a constant voltage generating circuit that can have a current capability.

[0006] A constant voltage generating circuit according to an embodiment of the present disclosure includes: a first transistor configured as a depletion-type N-channel MOSFET and having a first drain connected to an input voltage application terminal, a first source, and a first gate shorted to the first source; a second transistor configured as an N-channel MOSFET having a second drain connected to the first source, a second source, and a second gate; a third transistor configured as an N-channel MOSFET having a third drain connected to the first drain, a third gate connected to the first source, and a third source connected to the second gate; an output terminal connected to the second gate and configured to output an output voltage; The configuration is provided with the following. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing a configuration of a constant voltage generating circuit according to a comparative example. [Diagram 2] FIG. 2 is a diagram showing a configuration of the constant voltage generating circuit according to the first embodiment. [Diagram 3] FIG. 3 is a diagram showing a configuration of a constant voltage generating circuit according to the second embodiment. [Figure 4] FIG. 4 is a diagram showing a configuration of a constant voltage generating circuit according to the third embodiment. [Diagram 5] FIG. 5 is a diagram showing a configuration of a constant voltage generating circuit according to the fourth embodiment.

[0008] [Detailed Description] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.

[0009] <Comparative Example> FIG. 1 is a diagram showing a comparative example of a constant voltage generating circuit (basic configuration to be compared with the embodiments described later). The constant voltage generating circuit 1 of this comparative example is a so-called ED type reference voltage source. With reference to this diagram, the constant voltage generating circuit 1 includes a transistor M1 and a transistor M2. The transistor M1 is configured by a depletion type N-channel MOSFET. The transistor M2 is configured by an enhancement type N-channel MOSFET.

[0010] Note that the depletion type is one in which a drain current flows even when the gate-source voltage is 0 V. On the other hand, the enhancement type is one in which no drain current flows when the gate-source voltage is 0 V.

[0011] The drain of the transistor M1 is connected to an application terminal of the input voltage Vin. The source and back gate of the transistor M2 are connected to a ground terminal (an application terminal of the ground potential). The gate, source and back gate of the transistor M1 and the gate and drain of the transistor M2 are all connected to an output terminal Tout which is an application terminal of the output voltage Vout.

[0012] In the constant voltage generating circuit 1 of this comparative example, the gate and source of the transistor M1 are shorted. Therefore, the gate-source voltage Vgs1 of the transistor M1 is 0V. Therefore, the transistor M1 functions as a constant current source that generates a constant drain current Idd1. In other words, a constant bias current (=drain current Idd1) flows through the transistor M2. As a result, a constant output voltage Vout equivalent to the gate-source voltage Vgs2 of the transistor M2 is generated.

[0013] Here, assuming that the currents flowing through the transistors M1 and M2 operating in the saturation region are I1 and I2, respectively, the currents I1 and I2 are expressed by the following formulas (1a) and (1b).

[0014]

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[0015] In the above formulas (1a) and (1b), μ1 and μ2 are the carrier mobilities of the transistors M1 and M2, respectively. Cox is the oxide film capacitance of the transistors M1 and M2, respectively. W1 and W2 are the gate widths of the transistors M1 and M2, respectively. L1 and L2 are the gate lengths of the transistors M1 and M2, respectively. Vth1 and Vth2 are the threshold voltages of the transistors M1 and M2, respectively.

[0016] In the constant voltage generating circuit 1, I1=I2 holds. Therefore, the output voltage Vout is expressed by the following equation (2).

[0017]

number

[0018] The threshold voltage Vth1 of the depletion-type transistor M1 is a negative value. Therefore, the above formula (2) can be expressed as the following formula (3).

[0019]

number

[0020] Therefore, the temperature characteristics of the threshold voltages Vth1 and Vth2 can be offset by appropriately designing the W / L of each of the transistors M1 and M2.

[0021] However, the constant voltage generating circuit 1 of this comparative example does not have a current capacity, and when a load (not shown) connected to the output terminal Tout requires a current capacity, the output voltage Vout decreases. One example of a load requiring a current capacity is a resistive voltage divider circuit.

[0022] First Embodiment 2 is a diagram showing a configuration of a constant voltage generating circuit 11 according to the first embodiment of the present disclosure. The constant voltage generating circuit 11 includes transistors M1 and M2 as in the comparative example, and also includes transistors M3 and M4. Here, differences in the configuration from the comparative example will be mainly described.

[0023] The transistor M3 is configured by a depletion-type N-channel MOSFET. The drain of the transistor M3 is connected to the drain of the transistor M1. The gate of the transistor M3 is connected to the source of the transistor M1. The source of the transistor M3 is connected to the gate of the transistor M2. The gate of the transistor M2 is connected to the output terminal Tout. The output voltage Vout is output from the output terminal Tout.

[0024] By providing such a transistor M3, a source follower is configured. A current can be supplied from the output terminal Tout to the load LD via the transistor M3, and the constant voltage generating circuit 11 can have a current capability without affecting the output voltage Vout.

[0025] Moreover, the transistor M4 is configured by a depletion type N-channel MOSFET. The drain of the transistor M4 is connected to the source of the transistor M3. The gate and source of the transistor M4 are shorted. The source of the transistor M4 is connected to the ground terminal. The constant current source CI is configured by such a transistor M4. The constant current source CI can also be regarded as an active load formed by an active element (transistor M4). When the load LD is not connected, the leakage current flowing through the transistor M3 at high temperatures is absorbed by the constant current source CI, thereby preventing the output voltage Vout from increasing.

[0026] In addition, the constant voltage generating circuit 11 according to this embodiment can be configured with depletion-type transistors M1, M3, and M4 and an enhancement-type transistor M2. In other words, it can be configured with two types of elements. This makes it possible to suppress the effects of element variations and simplify the element layout.

[0027] <Second embodiment> 3 is a diagram showing a configuration of a constant voltage generating circuit 12 according to a second embodiment of the present disclosure. The configuration according to the second embodiment differs from that of the first embodiment (FIG. 2) in that switches SW1 and SW2 are provided.

[0028] The switch SW1 is connected between the source of the transistor M3 and the drain of the transistor M4. The switch SW2 is connected between the gate of the transistor M2 and the output terminal Tout.

[0029] When the output voltage Vout is applied to the load LD, the switch SW1 is in the OFF state and the switch SW2 is in the ON state, so that no current flows through the constant current source CI, thereby suppressing current consumption.

[0030] On the other hand, when the output voltage Vout is not applied to the load LD, the switch SW1 is in the on state and the switch SW2 is in the off state, so that the leakage current is absorbed by the constant current source CI, and the output voltage Vout can be prevented from increasing.

[0031] <Third embodiment> 4 is a diagram showing a configuration of a constant voltage generating circuit 13 according to a third embodiment of the present disclosure. In the constant voltage generating circuit 13, the transistor M2 is a depletion type having a p-type impurity implanted in its gate, and the transistors M1, M3, and M4 are depletion type having an n-type impurity implanted in its gate. Note that the depletion type transistors in the first and second embodiments described above have an n-type impurity implanted in their gates.

[0032] The depletion-type transistor M2, in which p-type impurities are implanted in the gate, can have a positive threshold voltage, and can be used instead of an enhancement-type transistor. Furthermore, the transistors M1 to M4 have a common device structure (particularly the portion below the gate). Therefore, the constant voltage generating circuit 13 of this embodiment can further suppress the effects of element variations. Also, the element layout can be simplified.

[0033] <Fourth embodiment> 5 is a diagram showing a configuration of a constant voltage generating circuit 14 according to a fourth embodiment of the present disclosure. The constant voltage generating circuit 14 differs from the first embodiment in that the transistor M3 is an enhancement type. Such a constant voltage generating circuit 14 can also have a current capability without affecting the output voltage Vout. However, if the transistor M3 is a depletion type, the operating voltage and therefore the input voltage Vin can be lowered.

[0034] <Other> In addition to the above-mentioned embodiment, various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. In other words, the above-mentioned embodiment should be considered to be illustrative and not restrictive in all respects, and the technical scope of the present invention should not be limited to the above-mentioned embodiment, but should be understood to include all modifications that fall within the meaning and scope equivalent to the scope of the claims.

[0035] Furthermore, the various embodiments described above may be implemented in any suitable combination unless there is a contradiction.

[0036] <Additional Notes> As described above, the constant voltage generating circuit (11) according to one aspect of the present disclosure includes a first transistor (M1) configured as a depletion-type N-channel MOSFET and having a first drain connected to an application terminal of an input voltage (Vin), a first source, and a first gate shorted to the first source; a second transistor (M2) configured as an N-channel MOSFET and having a second drain connected to the first source, a second source, and a second gate; a third transistor (M3) configured as an N-channel MOSFET and having a third drain connected to the first drain, a third gate connected to the first source, and a third source connected to the second gate; an output terminal (Tout) connected to the second gate and configured to output an output voltage (Vout); The first configuration includes the above.

[0037] This configuration solves the problem of providing a constant voltage generating circuit with current capability. That is, in a constant voltage generating circuit that generates a constant output voltage, a source follower is formed by the third transistor, and the constant voltage generating circuit can be provided with current capability without affecting the output voltage.

[0038] In the first configuration, the third transistor may be of the depletion type (second configuration).

[0039] In addition, in the first or second configuration, a constant current source (CI) may be further provided which is connected to the third source (third configuration).

[0040] In the third configuration, the constant current source may be configured as an active load having an active element (M4) (fourth configuration).

[0041] In the fourth configuration, the active element (M4) may be a depletion-type N-channel MOSFET with its gate and source shorted (fifth configuration).

[0042] In any one of the third to fifth configurations, a first switch (SW1) connected between the third source and the constant current source; The sixth configuration may further include a second switch (SW2) connected between the third source and the output terminal.

[0043] In any one of the first to sixth configurations, a fourth transistor (M4) is configured as a depletion-type N-channel MOSFET and has a fourth drain connected to the third source, a fourth source, and a fourth gate shorted to the fourth source, the second transistor is an enhancement type; The third transistor may be of the depletion type (seventh configuration).

[0044] In any one of the first to sixth configurations, a fourth transistor (M4) is configured as a depletion-type N-channel MOSFET and has a fourth drain connected to the third source, a fourth source, and a fourth gate shorted to the fourth source, the second transistor and the third transistor are depletion type; the first gate, the third gate, and the fourth gate are doped with n-type impurities; The second gate may be doped with p-type impurities (eighth configuration). [Industrial Applicability]

[0045] The present disclosure can be used in constant voltage generating circuits for various purposes. [Explanation of symbols]

[0046] 1,11~14 Constant voltage generation circuit CI constant current source LD load M1~M4 Transistors SW1, SW2 switches Tout output end

Claims

1. a first transistor configured as a depletion-type N-channel MOSFET and having a first drain connected to an input voltage application terminal, a first source, and a first gate shorted to the first source; a second transistor configured as an N-channel MOSFET and having a second drain connected to the first source, a second source, and a second gate; a third transistor configured as an N-channel MOSFET and having a third drain connected to the first drain, a third gate connected to the first source, and a third source connected to the second gate; an output terminal connected to the second gate and configured to output an output voltage; A constant voltage generating circuit comprising:

2. 2. The constant voltage generating circuit according to claim 1, wherein the third transistor is a depletion type.

3. The constant voltage generating circuit according to claim 1 , further comprising a constant current source connected to the third source.

4. 4. The constant voltage generating circuit according to claim 3, wherein the constant current source is configured as an active load having an active element.

5. 5. The constant voltage generating circuit according to claim 4, wherein the active element is a depletion type N-channel MOSFET having a gate and a source shorted therebetween.

6. a first switch connected between the third source and the constant current source; The constant voltage generating circuit according to claim 3 , further comprising: a second switch connected between the third source and the output terminal.

7. a fourth transistor configured as a depletion-type N-channel MOSFET and having a fourth drain connected to the third source, a fourth source, and a fourth gate shorted to the fourth source; the second transistor is an enhancement type; 2. The constant voltage generating circuit according to claim 1, wherein the third transistor is a depletion type.

8. a fourth transistor configured as a depletion-type N-channel MOSFET and having a fourth drain connected to the third source, a fourth source, and a fourth gate shorted to the fourth source; the second transistor and the third transistor are depletion type; the first gate, the third gate, and the fourth gate are doped with n-type impurities; 2. The constant voltage generating circuit according to claim 1, wherein the second gate is doped with a p-type impurity.

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