Reference voltage circuit

Abstract

The present invention provides a reference voltage circuit with low temperature dependence. The reference voltage circuit includes: a first NPN transistor, with its collector and base short-circuited and connected to a diode; a second NPN transistor, with its collector and base short-circuited and connected to a diode, its emitter connected to a first potential node, and operating at a current density greater than that of the first NPN transistor; a first resistor connected in series with the first NPN transistor; a second resistor, one end of which is connected to a circuit in which the first NPN transistor and the first resistor are connected in series; a third resistor, one end of which is connected to the collector of the second NPN transistor; a connection point for connecting the other end of the second resistor to the other end of the third resistor; an operational amplifier circuit, one end of which is connected to an inverting input terminal, one end of which is connected to a non-inverting input terminal, and one end of which is connected to an output terminal; and a current supply circuit connected to the collector of the first NPN transistor.

Description

Technical Field

[0001] The invention relates to a reference voltage circuit. Background Art

[0002] A reference voltage circuit using an NPN transistor has been proposed (for example, refer to Patent Document 1).

[0003] Figure 5 The reference voltage circuit described in Patent Document 1 includes a first NPN transistor Q41 and a second NPN transistor Q42, an operational amplifier OP, and resistors 41, 42, 43, and 44. By allowing currents of the same value to flow through the first NPN transistor Q41 and the second NPN transistor Q42 and adjusting (fine-tuning) the resistor 44, a reference voltage with no temperature characteristic is obtained.

[0004] [Prior art literature]

[0005] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-182113 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] Figure 6 Schematic diagram of the cross section of an NPN transistor. The NPN transistor comprises an emitter 31, a base 32, and a collector 33. When the NPN transistor is formed on a PSUB substrate 34, as shown in FIG. Figure 7 As shown, the NPN transistor has a parasitic diode 35 between the collector 33 and the PSUB substrate 34. At high temperatures, part of the current that should flow through the NPN transistor flows as leakage current through the parasitic diode 35.

[0009] In addition, Figure 5 In the reference voltage circuit, the size of the first NPN transistor Q41 is set larger than that of the second NPN transistor Q42. Therefore, the size of the parasitic diode is also larger than that of the second NPN transistor Q42. In addition, the larger the size of the parasitic diode, the greater the leakage current. Therefore, the leakage current flowing through the parasitic diode is larger in the first NPN transistor Q41 than in the second NPN transistor Q42. As a result, the currents flowing through the first NPN transistor Q41 and the second NPN transistor Q42 deviate from the same current value originally set at high temperatures. Figure 5 The reference voltage circuit has a large temperature dependence.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a reference voltage circuit having low temperature dependence.

[0011] [Technical means to solve the problem]

[0012] The reference voltage circuit of the present invention includes: a first NPN transistor, the collector and base of which are short-circuited and connected to a diode; a second NPN transistor, the collector and base of which are short-circuited and connected to a diode, the emitter of which is connected to a first potential node, and operates at a current density greater than that of the first NPN transistor; a first resistor connected in series with the first NPN transistor; a second resistor, one end of which is connected to a circuit in which the first NPN transistor and the first resistor are connected in series; a third resistor, one end of which is connected to the collector of the second NPN transistor; a connection point for connecting the other end of the second resistor to the other end of the third resistor; an operational amplifier circuit, having an inverting input terminal connected to one end of the second resistor, a non-inverting input terminal connected to one end of the third resistor, and an output terminal connected to the connection point; and a current supply circuit connected to the collector of the first NPN transistor.

[0013] [Effects of the Invention]

[0014] According to the present invention, a reference voltage with low temperature dependence can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a circuit diagram showing a first configuration example of a reference voltage circuit according to an embodiment.

[0016] Figure 2 This is a circuit diagram showing a second configuration example of the reference voltage circuit according to the embodiment.

[0017] Figure 3 This is a circuit diagram showing a third configuration example of the reference voltage circuit according to the embodiment.

[0018] Figure 4 This is a circuit diagram showing a fourth configuration example of the reference voltage circuit according to the embodiment.

[0019] Figure 5 This is a circuit diagram showing an example of a reference voltage circuit including a conventional NPN transistor.

[0020] Figure 6 It is a cross-sectional view showing the structure of a typical NPN transistor.

[0021] Figure 7 This is a circuit diagram showing an equivalent circuit of a typical NPN transistor.

[0022] Explanation of symbols

[0023] 1, 2, 7: NPN transistors

[0024] 3, 4, 5, 14, 15, 16, 44: resistors

[0025] 6: Operational Amplifier

[0026] 7a: Diode

[0027] 8, 9: P-channel MOS transistor

[0028] 10, 11, 12, 13, 20: Reference voltage circuit

[0029] 17, 18: Connection points

[0030] 21: Current supply circuit

[0031] 31: Emitter

[0032] 32: Base

[0033] 33: Collector

[0034] 34: PSUB substrate

[0035] 35: Parasitic diode

[0036] Q41: First NPN transistor

[0037] Q42: Second NPN transistor DETAILED DESCRIPTION

[0038] Hereinafter, a reference voltage circuit according to an embodiment of the present invention will be described with reference to the drawings.

[0039] Figure 1 1 is a circuit diagram of a reference voltage circuit 10 as an example (first configuration example) of a reference voltage circuit according to an embodiment. The reference voltage circuit 10 includes a conventional reference voltage circuit 20 and a current supply circuit 21 .

[0040] Conventional reference voltage circuit 20 includes: NPN transistors 1 and 2; resistors 3, 4, and 5; an operational amplifier 6; and an OUT terminal. Here, NPN transistor 2 is larger than NPN transistor 1. Resistors 4 and 5 have the same resistance value. Current supply circuit 21 includes: NPN transistor 7; and P-channel metal oxide semiconductor (MOS) transistors 8 and 9.

[0041] The connection of the existing reference voltage circuit 20 is described. The base terminal of NPN transistor 1 is connected to the collector terminal and to one end of resistor 4. The emitter terminal is connected to the ground (GND) power supply. The base terminal of NPN transistor 2 is connected to the collector terminal and to one end of resistor 5. The emitter terminal is connected to the GND power supply via resistor 3. In addition, the base terminal and collector terminal of NPN transistor 2 are connected to the drain terminal of P-channel MOS transistor 9 of current supply circuit 21. The other end of resistor 4 and the other end of resistor 5 are connected to connection point 17. The non-inverting input terminal of operational amplifier 6 is connected to the collector terminal of NPN transistor 1, the inverting input terminal is connected to the collector terminal of NPN transistor 2, and the output terminal is connected to connection point 17 and the OUT terminal. The description of the power supply of operational amplifier 6 is omitted.

[0042] The connection of current supply circuit 21 will be described. The source terminal of P-channel MOS transistor 8 is connected to the VDD power supply, and the gate terminal is connected to the drain terminal, the gate terminal of P-channel MOS transistor 9, and the collector terminal of NPN transistor 7. The source terminal of P-channel MOS transistor 9 is connected to the VDD power supply, the gate terminal is connected to the gate terminal of P-channel MOS transistor 8, and the drain terminal is connected to the collector terminal of NPN transistor 2 in the existing reference voltage circuit 20. The collector terminal of NPN transistor 7 is connected to the drain terminal of P-channel MOS transistor 8, and the base terminal is connected to the emitter terminal and the GND power supply. P-channel MOS transistor 8 and P-channel MOS transistor 9 form a current mirror circuit.

[0043] The operation of conventional reference voltage circuit 20 will be described. Operational amplifier 6 amplifies the difference between the voltage generated in resistor 3 and base-emitter voltage VBE2 of NPN transistor 2, and base-emitter voltage VBE1 of NPN transistor 1. The output voltage of operational amplifier 6 is applied to resistors 4 and 5.

[0044] Here, when the output voltage of operational amplifier 6 falls below a specified value, the current flowing through resistors 4 and 5 decreases below the specified value. The resistance values ​​of resistors 4 and 5 are set relatively large, and the voltage drop across them is set to be greater than the base-emitter voltage VBE1 of NPN transistor 1 and the base-emitter voltage VBE2 of NPN transistor 2. Base-emitter voltage VBE1 of NPN transistor 1 and base-emitter voltage VBE2 of NPN transistor 2 are substantially the same as when the voltage is at the specified value. Therefore, if the resistance value of resistor 3 is set to R3 and the current flowing through resistor 3 is set to IR3, the input potential of the non-inverting input terminal of operational amplifier 6 is determined by voltage VBE1, and the input potential of the inverting input terminal is determined by voltage VBE2 + resistance value R3 × current value IR3. Since the current value IR3 is smaller than when the output voltage is a predetermined value, the input voltage of the non-inverting input terminal is lower than the input potential of the inverting input terminal, and the output voltage of the operational amplifier 6 increases and reaches a stable value.

[0045] When the output voltage of the operational amplifier 6 is higher than the specified value, the voltage generated in the resistor 3 becomes higher. For the same reason as described above, the input voltage of the inverting input terminal of the operational amplifier 6 becomes higher than the input voltage of the non-inverting input terminal, and the output voltage of the operational amplifier drops to a stable value.

[0046] When reference voltage circuit 20 reaches a stable state, the input voltages at the non-inverting and inverting input terminals of operational amplifier 6 are at the same potential. Therefore, currents of equal magnitude flow through NPN transistor 1 and NPN transistor 2. As described above, NPN transistor 2 has a larger transistor size than NPN transistor 1. NPN transistor 1 operates with a higher current density than NPN transistor 2. The difference voltage ΔVBE between the base-emitter voltage VBE1 of NPN transistor 1 and the base-emitter voltage VBE2 of NPN transistor 2 is expressed by the following equation.

[0047] [Formula 1]

[0048] ΔVBE=VBE1-VBE2=(KT / q)×lnN

[0049] Here, K is Boltzmann's constant, T is absolute temperature, q is charge, and N is the ratio of the transistor sizes of NPN transistor 1 to NPN transistor 2 .

[0050] Therefore, a current having a voltage of ΔVBE / resistance value R3 flows through resistor 3, and this current also flows through resistor 5. Since the same current flows through NPN transistors 1 and 2, and the same current flows through resistors 4 and 5, the output voltage of operational amplifier 6 is expressed by the following equation.

[0051] [Formula 2]

[0052] VOUT=VBE1+(ΔVBE / R3)×R4

[0053] Here, R4 is the resistance value of resistor 4. The value of voltage ΔVBE is proportional to the absolute temperature T as shown in the previous formula. Therefore, as the temperature increases, the value of voltage ΔVBE increases. However, as the temperature increases, voltage VBE1 decreases. Therefore, by appropriately selecting the resistance values ​​of resistors 3, 4, and 5, a reference voltage with no temperature characteristics can be generated.

[0054] Furthermore, when a reference voltage circuit is built into an integrated circuit, an NPN transistor may be formed on a PSUB substrate. Figure 6 A cross-sectional view of an NPN transistor formed on a PSUB substrate is shown. Figure 7 An equivalent circuit of an NPN transistor formed on a PSUB substrate is shown.

[0055] The first N-type diffusion layer of the NPN transistor formed on PSUB substrate 34 serves as collector 33, the P-type diffusion layer serves as base 32, and the second N-type diffusion layer serves as emitter 31. PSUB substrate 34 and the first N-type diffusion layer serving as collector 33 form a parasitic diode 35.

[0056] Since the parasitic diode 35 is reverse-biased during NPN transistor operation, it generally does not affect the operation of the NPN transistor. However, a small leakage current flows from the cathode to the anode in the reverse-biased parasitic diode 35. This leakage current flowing through the parasitic diode 35 is temperature-dependent, with higher leakage current flowing at higher temperatures.

[0057] Figure 1 Conventional voltage reference circuit 20 shown includes parasitic diodes in both NPN transistor 1 and NPN transistor 2. A portion of the current flowing through each of NPN transistors 1 and 2 flows to the GND power supply via the parasitic diodes. Since NPN transistor 2 is larger than NPN transistor 1, the parasitic diode of NPN transistor 2 is also larger than that of NPN transistor 1.

[0058] To generate a reference voltage with minimal temperature dependence, equal currents must flow through NPN transistor 1 and NPN transistor 2. However, because the parasitic diode in NPN transistor 2 is larger than that in NPN transistor 1, leakage current through the parasitic diode increases at high temperatures. At high temperatures, the current flowing through NPN transistor 2 decreases more than the current flowing through NPN transistor 1. This creates a difference in current flowing through NPN transistor 1 and NPN transistor 2. Conventional reference voltage circuits formed on PSUB substrates cannot generate a reference voltage with minimal temperature dependence, and the generated reference voltage exhibits temperature dependence.

[0059] Therefore, in this embodiment, current supply circuit 21 is connected to the collector of NPN transistor 2. NPN transistor 7 of current supply circuit 21 has a parasitic diode, and leakage current flows through it in the same manner as NPN transistor 2. Current supply circuit 21 supplies the leakage current flowing through NPN transistor 7 to the collector of NPN transistor 2 via a current mirror circuit formed by P-channel MOS transistors 8 and 9.

[0060] By adjusting the transistor size of NPN transistor 7 and the magnetic mirror ratio of the current mirror circuit, the currents flowing through NPN transistor 1 and NPN transistor 2 can be set to be equal. Specifically, the transistor size of NPN transistor 7 can be adjusted by connecting multiple NPN transistors in parallel to form NPN transistor 7, and then separating a portion of the multiple transistors from the circuit as needed through fine-tuning. Similarly, the magnetic mirror ratio of the current mirror circuit can be adjusted by connecting multiple P-channel MOS transistors in parallel to form a transistor that constitutes the current mirror circuit, and then separating a portion of the multiple P-channel MOS transistors from the circuit as needed through fine-tuning.

[0061] Furthermore, here, the resistor 3 is connected between the NPN transistor 2 and the GND power supply, but Figure 2 As in the reference voltage circuit 11 of the second structural example shown in FIG. 1 , the resistor 3 is connected between the resistor 5 and the NPN transistor 2, the inverting input terminal of the operational amplifier 6 is connected to the connection point between the resistor 3 and the resistor 5, and the current supply circuit 21 can also be connected to the reference voltage circuit 11 of the second structural example shown in FIG. Figure 1 Similarly, the emitter of the NPN transistor 2 can be connected to the GND power supply by connecting to the collector of the NPN transistor 2 .

[0062] In addition, if Figure 3As shown in the third exemplary configuration of reference voltage circuit 12, NPN transistor 7 may be configured as diode 7a. Diode 7a has its cathode connected to the drain of P-channel MOS transistor 8, and its anode connected to the GND power supply. Diode 7a is a diode consisting solely of the parasitic diode of NPN transistor 7, and the same leakage current as that of NPN transistor 7 flows through it.

[0063] In addition, if Figure 4 As shown in the fourth configuration example, the resistors 4 and 5 may include resistors 14, 15, and 16. Resistor 14 has one end connected to the collector terminal of NPN transistor 1 and the other end connected to connection point 18. Resistor 15 has one end connected to the collector terminal of NPN transistor 2 and the other end connected to connection point 18. Resistor 16 has one end connected to connection point 18 and the other end connected to the output terminal of operational amplifier 6. The fourth configuration example is a configuration in which resistors 4 and 5 are partially replaced by resistor 16.

[0064] The reference voltage circuit 10 of this embodiment includes an existing reference voltage circuit 20 and a current supply circuit 21. By utilizing the current supply circuit 21 to compensate for the leakage current flowing through the parasitic diode of the NPN transistor 2, the current flowing through the NPN transistor 1 body and the NPN transistor 2 body that generate the reference voltage can be made the same regardless of temperature, thereby generating a reference voltage with low temperature dependence.

[0065] Furthermore, the present invention is not limited to the embodiments described above. In addition to the examples described above, various embodiments are possible during implementation. Various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. For example, each switch described in the embodiments of the invention may include a PMOS transistor or an NMOS transistor. These embodiments and their variations are intended to be within the scope and spirit of the invention and are encompassed by the invention set forth in the claims and their equivalents.

Claims

1. A reference voltage circuit, characterized in that: include: a first NPN transistor having a collector and a base short-circuited and connected to a diode; a second NPN transistor having a collector and a base short-circuited and connected to a diode, an emitter connected to the first potential node, and operating at a current density greater than that of the first NPN transistor; a first resistor connected in series with the first NPN transistor; a second resistor, one end of which is connected to a circuit in which the first NPN transistor and the first resistor are connected in series; a third resistor, one end of which is connected to the collector of the second NPN transistor; a connection point for connecting the other end of the second resistor and the other end of the third resistor; an operational amplifier circuit, wherein an inverting input terminal is connected to one end of the second resistor, a non-inverting input terminal is connected to one end of the third resistor, and an output terminal is connected to the connection point; and A current supply circuit is connected to the collector of the first NPN transistor, wherein The current supply circuit supplies a current equal to a leakage current of the first NPN transistor to the collector of the first NPN transistor so that a current flowing through the first NPN transistor is equal to a current flowing through the second NPN transistor.

2. The reference voltage circuit according to claim 1, wherein: The current supply circuit includes a diode whose anode is connected to the first potential node, and a fourth transistor and a fifth transistor forming a current mirror circuit. The current flowing through the diode is supplied to the collector of the first NPN transistor via the current mirror circuit.

3. The reference voltage circuit according to claim 1, wherein: The current supply circuit includes a third NPN transistor with an emitter and a base short-circuited and connected to a diode, and a fourth transistor and a fifth transistor forming a current mirror circuit. The current flowing through the third NPN transistor is supplied to the collector of the first NPN transistor via the current mirror circuit.

4. The reference voltage circuit according to claim 1, wherein: The connection point is connected to the output terminal of the operational amplifier circuit via a fourth resistor.

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