Reference current source circuit

Abstract

The maximum value of the temperature gradient of the reference current generated by the reference current source circuit is increased independently of the process. [Solution] The input circuit Q200 includes an input circuit A200 and a feedback circuit F200 that provides feedback from the output of the input circuit Q200 to the input. The input circuit Q200 includes a resistor Rref, one end of which is connected to a control node CN and the other end of which a reference voltage Vref is applied, and a constant voltage generator that turns ON when a voltage above a certain level is applied. The feedback circuit F200 includes a feedback unit that maintains the voltage at the control node CN at a constant voltage Vbe by providing feedback from the output node of the constant voltage generator to the control node CN, and an amplification unit that amplifies the current flowing through the resistor Rref and outputs a reference current Iout.

Description

【Technical Field】 【0001】 This invention relates to a reference current source circuit that generates a constant reference current. 【Background Art】 【0002】 As current source circuits used in analog circuits such as amplifiers, there are a PTAT (Proportional To Absolute Temperature) current source circuit that generates a reference current having a positive temperature gradient and a CTAT (Complementary To Absolute Temperature) current source circuit that generates a reference current having a negative temperature gradient. Patent Document 1 discloses a reference current source circuit that includes this PTAT current source circuit and CTAT current source circuit and can generate a reference current with a desired temperature gradient. [Figure 6] [Figure 7] FIG. 6 is a circuit diagram showing the configuration of the reference current source circuit <000085>100 disclosed in Patent Document <000086>1. As shown in FIG. <00087>6, the reference current source circuit <000088>100 includes a CTAT current source circuit <000089>10, a PTAT current source circuit <000090>20, and an addition circuit <000091>30. 【0004】 The CTAT current source circuit <000092>10 has P-channel MOS transistors <000093>M11 and <000094>M12, N-channel MOS transistors <000095>M13 and <000096>M14, a bipolar transistor <000097>Q11, and a resistor <000098>R11. The MOS transistors <000099>M11 to <000100>M14 form a feedback circuit <000101>F11. 【0005】 In the CTAT current source circuit <000102>10, since feedback is performed through the feedback circuit <000103>F11, a current <000104>I11 that makes the voltage generated in the resistor <000105>R11 equal to the base-emitter voltage <000106>Vbe of the bipolar transistor <000107>Q11 flows through the resistor <000108>R11 as shown in the following equation. I11 = Vbe / R11 ……(1) 【0006】 This current <000109>I11 is transmitted to the addition circuit <000110>30 through the MOS transistor <000111>M12. Since the base-emitter voltage <000112>Vbe has a negative temperature gradient, the current <000113>I11 also has a negative potential gradient. 【0007】 The PTAT current source circuit 20 includes P-channel MOS transistors M21 and M22, N-channel MOS transistors M23 and M24, bipolar transistors Q21 and Q22, and a resistor R21. MOS transistors M21 to M24 constitute a feedback circuit F21. 【0008】 In the PTAT current source circuit 20, feedback is performed via the feedback circuit F21, so the current I21 shown in the following equation flows through the resistor R21. I21=V T ·In(n) / R21 ……(2) Here, n is the Miller ratio of MOS transistors M23 and M24. Also, V T =kT / q, where k is Boltzmann's constant, T is the absolute temperature, and q is the charge of the electron. This current I21 has a positive temperature gradient and is transmitted to the adder circuit 30 via the MOS transistor M22. 【0009】 The adder circuit 30 has MOS transistors M31, M32, M33, and M34. Here, MOS transistor M31 forms a current mirror with MOS transistor M12 of the CTAT current source circuit 10, and MOS transistor M32 forms a current mirror with MOS transistor M22 of the PTAT current source circuit 20. In addition, in the adder circuit 30, MOS transistors M33 and M34 form a current mirror. Then, in the adder circuit 30, a reference current Iout = I11m + I21m is generated in MOS transistor M34 by weighted summing of the current I11 in the CTAT current source circuit 10 and the current I21 in the PTAT current source circuit 20. [Prior art documents] [Patent Documents] 【0010】 [Patent Document 1] Japanese Patent Application Publication No. 11-231955 [Overview of the Initiative] [Problems that the invention aims to solve] 【0011】 According to the technology disclosed in Patent Document 1, by adjusting the Miller ratios of MOS transistors M12 and M31 and the Miller ratios of MOS transistors M22 and M32, the temperature gradient of the reference current Iout can be adjusted within a range from the maximum value of the negative temperature gradient of current I11 to the maximum value of the positive temperature gradient of current I21 (see Figure 7). 【0012】 However, there is no existing technology to generate a temperature gradient greater than that obtained from a transistor. Therefore, conventionally, a temperature gradient greater than that achievable by a single element has been obtained by combining the temperature characteristics of transistors and resistors formed by the process. However, the temperature gradient obtained in this way has the problem of being unstable because it depends on the process. 【0013】 This invention has been made in view of the circumstances described above, and aims to provide a technical means for increasing the maximum value of the temperature gradient of the reference current generated by a reference current source circuit, without depending on the process. [Means for solving the problem] 【0014】 This invention provides a reference current source circuit that includes an input circuit and a feedback circuit that provides feedback from the output of the input circuit to the input, wherein the input circuit includes a resistor with one end connected to a control node and a reference voltage applied to the other end, and a constant voltage generating unit that turns ON when a voltage above a certain voltage is applied, and the feedback circuit includes a feedback unit that maintains the voltage at the control node at the constant voltage by providing feedback from the output node of the constant voltage generating unit to the control node, and an amplification unit that amplifies the current flowing through the resistor and outputs a reference current. 【0015】 According to this invention, the maximum value of the temperature gradient of the reference current generated by the reference current source circuit can be increased independently of the process. [Brief explanation of the drawing] 【0016】 [Figure 1] This is a circuit diagram showing the configuration of a reference current source circuit according to the first embodiment of the present invention. [Figure 2] This is a diagram showing the operation of the embodiment. [Figure 3] This is a diagram showing the operation of the embodiment. [Figure 4] This is a circuit diagram showing the configuration of a reference current source circuit according to the second embodiment of the present invention. [Figure 5] This is a circuit diagram showing the configuration of a reference current source circuit according to the third embodiment of the present invention. [Figure 6] This is a circuit diagram showing the configuration of a conventional reference current source circuit. [Figure 7] This is a diagram showing the operation of the reference current source circuit. 【Embodiments for Carrying Out the Invention】 【0017】 Hereinafter, embodiments of the present invention will be described with reference to the drawings. 【0018】 <First Embodiment> FIG. 1 is a circuit diagram showing the configuration of a reference current source circuit 200 according to the first embodiment of the present invention. This reference current source circuit 200 is a CTAT current source circuit that generates a reference current Iout having a negative temperature gradient, and includes an input circuit A200 and a feedback circuit F200. 【0019】 The input circuit A200 has a resistor Rref having one end connected to a control node CN and a reference voltage Vref applied to the other end, and an npn bipolar transistor Q201. The bipolar transistor Q201 has its collector, which is the first output terminal, connected to the feedback circuit F200, its emitter, which is the second output terminal, grounded, and its base, which is the control terminal, connected to the control node CN. The bipolar transistor Q201 is a constant voltage generation unit that turns ON when a base-emitter voltage Vbe of a certain voltage or higher is applied. 【0020】 The feedback circuit F200 includes P-channel MOS transistors M201 and M202, an N-channel MOS transistor M203, and a constant current source 205. The constant current source 205 is interposed between the power supply VDD and the collector of the bipolar transistor Q201. The sources of MOS transistors M201 and M202 are connected to the power supply VDD, and the gates of MOS transistors M201 are connected to the drain of MOS transistor M201. The drain of MOS transistor M203 is connected to the drain of MOS transistor M201, the gate is connected to the collector of bipolar transistor Q201, and the source is connected to the control node CN. 【0021】 The MOS transistor M203 is a feedback unit that maintains the voltage at control node CN at a constant voltage Vbe by providing feedback from the output node of the constant voltage generation unit, i.e., from the collector (first output terminal) of the bipolar transistor Q201 to control node CN. 【0022】 Since the control node CN is maintained at a constant voltage Vbe, a current Iref = (Vbe - Vref) / Rref flows through the resistor Rref. This current Iref flows through MOS transistor M203 to MOS transistor M201. 【0023】 MOS transistors M201 and M202 constitute a current mirror. This current mirror is an amplifier that amplifies the current Iref flowing through resistor Rref and outputs a reference current Iout. The gain of this amplifier is the mirror ratio of the current mirror consisting of MOS transistors M201 and M202. The mirror ratio is the ratio of the transistor size (channel width W / channel length L) of MOS transistor M201 to the transistor size of MOS transistor M202. 【0024】 Next, the operation of this embodiment will be described with reference to Figures 2 and 3. In Figures 2 and 3, the horizontal axis represents temperature. In Figure 2, the vertical axis represents the applied voltage relative to the resistance Rref. In Figure 3, the vertical axis represents the current Iref and the reference current Iout. 【0025】 In this example, a reference voltage Vref = 200mV is applied to the resistor Rref. Therefore, the temperature characteristic of the applied voltage with respect to the resistor Rref is shifted to the lower voltage side by 200mV, as shown in Figure 2. This creates a margin to increase the negative temperature gradient of the reference current Iout. 【0026】 Furthermore, in this example, the mirror ratio m of the current mirror consisting of MOS transistors M201 and M202 is 1.6. Therefore, as shown in Figure 3, the negative temperature gradient of the reference current Iout is amplified 1.6 times by the current mirror. 【0027】 As described above, according to this embodiment, the temperature gradient of the reference current in the reference current source circuit can be increased beyond the range of the temperature gradient determined by the process. Furthermore, according to this embodiment, by applying a reference voltage Vref to the resistor Rref, the negative temperature gradient of the reference current Iout can be increased without changing the minimum value of the reference current Iout, as shown in Figure 3. 【0028】 In this embodiment, a bipolar transistor Q201 is used as the constant voltage generator, but a MOS transistor in an NMOS circuit or an N-channel MOS transistor in a CMOS circuit may also be used as the constant voltage generator. Furthermore, in this embodiment, the reference voltage Vref may have a flat temperature characteristic, but if the reference voltage Vref has a positive temperature gradient, the negative temperature gradient of the reference current Iout can be further increased. 【0029】 <Second Embodiment> Figure 4 is a circuit diagram showing the configuration of a reference current source circuit 201, which is a second embodiment of the present invention. This reference current source circuit 201 is a CTAT current source circuit that generates a reference current Iout having a negative temperature gradient, and includes an input circuit A201 and a feedback circuit F201. 【0030】 The input circuit A201 has a resistor Rref, one end of which is connected to the control node CN and the other end to which a reference voltage Vref is applied, and a pnp type bipolar transistor Q202. The collector, which is the first output terminal, and the base, which is the control terminal, of the bipolar transistor Q202 are grounded, and the emitter, which is the second output terminal, is connected to the feedback circuit F201. The bipolar transistor Q202 is a constant voltage generator that turns ON when a base-emitter voltage Vbe of a certain voltage or higher is applied. 【0031】 The feedback circuit F201 has P-channel MOS transistors M211, M212, and M213, and N-channel MOS transistors M221 and M222. The sources of MOS transistors M211, M212, and M213 are each connected to the power supply VDD, and the gates of each MOS transistor are each connected to the drain of MOS transistor M211. The drain of MOS transistor M221 is connected to the drain of MOS transistor M211. The drain of MOS transistor M222 is connected to the drain of MOS transistor M212. The gates of MOS transistors M221 and M222 are each connected to the drain of MOS transistor M212. The source of MOS transistor M221 is connected to control node CN. The source of MOS transistor M222 is connected to the collector of bipolar transistor Q202. 【0032】 MOS transistors M222 and M221 are feedback units that maintain the voltage at control node CN at a constant voltage Vbe by providing feedback from the output node of the constant voltage generation unit, i.e., from the emitter of bipolar transistor Q202 to control node CN. 【0033】 Since the control node CN is maintained at a constant voltage Vbe, a current Iref = (Vbe - Vref) / Rref flows through the resistor Rref. This current Iref flows through MOS transistor M221 to MOS transistor M211. 【0034】 MOS transistors M211 and M213 constitute a current mirror. This current mirror is an amplifier that amplifies the current Iref flowing through resistor Rref and outputs a reference current Iout. The gain of this amplifier is the mirror ratio of the current mirror consisting of MOS transistors M211 and M213. 【0035】 In this embodiment, the same effects as in the first embodiment can be obtained. In this embodiment, a pnp type bipolar transistor Q202 is used as the constant voltage generator, but an npn type bipolar transistor may also be used as the constant voltage generator. In this embodiment, the reference voltage Vref may have a flat temperature characteristic, but if the reference voltage Vref is given a positive temperature gradient, the negative temperature gradient of the reference current Iout can be further increased. 【0036】 <Third Embodiment> Figure 5 is a circuit diagram showing the configuration of a reference current source circuit 202, which is a third embodiment of this invention. This reference current source circuit 202 is a CTAT current source circuit that generates a reference current Iout having a negative temperature gradient, and has a configuration that is basically the same as the reference current source circuit 200a of the first embodiment, with the addition of a Vref generation circuit 300 and a starter circuit 400. In Figure 5, the wiring to the back gates of the MOS transistors (the substrate region or well on which the MOS transistors are formed) is shown, which was omitted from the illustration in Figure 1. Except for some MOS transistors M28 and M32, the back gates of the P-channel MOS transistors are connected to the power supply VDD, and the back gates of the N-channel MOS transistors are grounded. 【0037】 In the reference current source circuit 200a, a P-channel MOS transistor M205 is provided as the constant current source I205 of the first embodiment. In addition, a resistor R7 is inserted between the emitter of the bipolar transistor Q201 of the first embodiment and ground. 【0038】 The Vref generation circuit 300 is a circuit that generates a reference voltage Vref relative to the reference current source circuit 200a, and includes a resistor R4 and a P-channel MOS transistor M32. One end of resistor R4 is connected to the starter circuit 400 and the other end is grounded. The source and back gate of the MOS transistor M32 are connected to resistor Rref, the drain is grounded, and the gate is connected to the connection point between the starter circuit 400 and resistor R4. 【0039】 The starter circuit 400 is a circuit that controls the Vref generation circuit 300 and the reference current source circuit 200a, and includes P-channel MOS transistors M27, M51, M46 and M31, an N-channel MOS transistor M28, npn-type bipolar transistors Q41 and Q40, and resistors R40 and R41. 【0040】 The source of MOS transistor M27 is connected to the power supply VDD, and its gate and drain are commonly connected to the drain of MOS transistor M28 and the gate of MOS transistor M205. MOS transistors M27 and M205 form a current mirror, so that a current proportional to the current flowing through MOS transistor M28 flows through MOS transistor M205 (i.e., constant current source 205). 【0041】 MOS transistors M51, M46, and M31 have their respective sources connected to the power supply VDD, and their respective gates are commonly connected to the drain of MOS transistor 46. A start current Ist is drawn from the drain of MOS transistor M46 by a control means (not shown). 【0042】 Bipolar transistor Q41 has its emitter grounded and its collector connected to the drain of MOS transistor M51. Bipolar transistor Q40 has its emitter grounded via resistor R40 and its collector connected to the drain of MOS transistor M46. Bipolar transistors Q41 and Q40 have their bases connected in common, with resistor R41 inserted between this common connection node and ground. MOS transistor M28 has its source and back gate connected to the common connection node of the bases of bipolar transistors Q41 and Q40, its gate connected to the collector of bipolar transistor Q41, and its drain connected to the drain of MOS transistor M27. 【0043】 In the start circuit 400, current is drawn from MOS transistor M27 by MOS transistor M28, and this current is divided and flows into the base of bipolar transistor Q41, resistor R41, and the base of bipolar transistor Q40. The current flowing through MOS transistor M27 is also transmitted to MOS transistor M205. 【0044】 Furthermore, when the start current Ist is drawn from the drain of MOS transistor M46, a current proportional to the start current Ist is supplied from MOS transistor M51 to bipolar transistor Q41. Also, because resistor R41 is connected to bipolar transistor Q40, less current is supplied from MOS transistor M46 to bipolar transistor Q40 than is supplied to bipolar transistor Q41. As a result, bipolar transistors Q41 and Q40 turn ON. 【0045】 MOS transistors M46 and M31 constitute a current mirror. Therefore, a current proportional to the start current Ist flows through MOS transistor M31, and this current flows through resistor R4 of the Vref generation circuit 300. The reference voltage Vref, which is the source potential of MOS transistor M32, increases in accordance with the voltage generated across resistor R4. 【0046】 Here, the threshold voltage Vth of MOS transistor M32 has a negative temperature gradient. Also, the current flowing through resistor R4 has a positive temperature gradient because it depends on the base-emitter voltage Vbe of bipolar transistors Q41 and Q40. Therefore, the source-drain voltage Vds of MOS transistor M32, i.e., the reference voltage Vref, has a flat temperature characteristic. At this time, the drain current flowing through MOS transistor M32 is a current with a negative temperature gradient. Accordingly, by making the channel width W of MOS transistor M32 sufficiently large in the transistor size W / L, the positive temperature gradient of the overdrive voltage Vov = Vgs - Vth (because Vth has a negative temperature gradient) of MOS transistor M32 is canceled out by the negative temperature gradient of the drain current and becomes negligible. 【0047】 On the other hand, by increasing the channel length L of the MOS transistor M32, which is part of the transistor size W / L, and raising the overdrive voltage Vov of the MOS transistor M32, it is possible to introduce a positive temperature gradient to the reference voltage Vref. 【0048】 As described above, according to this embodiment, a reference voltage Vref with a desired temperature gradient can be applied to the reference current source circuit, and a reference current Iout with a desired temperature gradient can be generated. In this embodiment, a Vref generation circuit and a starter circuit were added to the reference current source circuit of the first embodiment, but a Vref generation circuit and a starter circuit may also be added to the reference current source circuit of the second embodiment. [Explanation of symbols] 【0049】 200, 201, 202, 200a... Reference current source circuit, M201, M202, M203, M211, M212, M213, M221, M222, M205, M51, M46, M31, M27, M28, M32... MOS transistors, Q201, Q202, Q41, Q42... Bipolar transistors, Rref, R4, R7, R41, R40... Resistors, 205... Constant current source.

Claims

[Claim 1] It includes an input circuit and a feedback circuit that provides feedback from the output of the input circuit to the input, The aforementioned input circuit is A resistor with one end connected to a control node and the other end to which a reference voltage is applied, It includes a constant voltage generating unit that turns ON when a voltage above a certain level is applied, The aforementioned feedback circuit is A feedback unit that maintains the voltage of the control node at the constant voltage by providing feedback from the output node of the constant voltage generation unit to the control node, A reference current source circuit including an amplification unit that amplifies the current flowing through the resistor and outputs a reference current. [Claim 2] The constant voltage generating unit includes a control terminal, a first output terminal, and a second output terminal, and includes a transistor that turns ON between the first output terminal and the second output terminal when the voltage between the control terminal and the second output terminal becomes equal to or greater than a threshold voltage. The control terminal is connected to the control node, The feedback unit provides feedback from the first output terminal to the control node. The reference current source circuit according to claim 1. [Claim 3] The constant voltage generating unit includes a control terminal, a first output terminal, and a second output terminal, the control terminal and the first output terminal are connected in common, and the unit includes a transistor that turns ON between the first output terminal and the second output terminal when the voltage between the control terminal and the second output terminal exceeds a threshold voltage. The feedback unit provides feedback from the second output terminal to the control node. The reference current source circuit according to claim 1. [Claim 4] The reference current source circuit according to claim 1, wherein the amplification section is a current mirror consisting of a plurality of transistors. [Claim 5] A reference current source circuit according to claim 1, comprising a reference voltage generating circuit that generates a reference voltage having a flat temperature characteristic. [Claim 6] A reference current source circuit according to claim 1, comprising a reference voltage generating circuit that generates a reference voltage having a positive temperature gradient.

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