JP2006119758A - Low-voltage operating circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-voltage operating circuit for effectively operating a band-gap reference voltage generating circuit or a constant-current generating circuit. <P>SOLUTION: The low-voltage operating circuit, for operating a band-gap reference voltage generating circuit having both a current mirror circuit and an output transistor to which the output current of the current mirror circuit is supplied, includes a first transistor connected in series with one diode-connected transistor that forms the current mirror circuit; a second transistor connected in series with the output transistor and having the first transistor and a control electrode commonly connected thereto; and a plurality of third transistors that keep below a predetermined value the potential difference between the control electrode of the first transistor and an electrode located on the side of the one transistor of the first transistor. The first transistor, the second transistor and the plurality of third transistors constitute the current mirror circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a low voltage operation circuit that operates a constant current generation circuit, a reference voltage generation circuit, and the like with a low power supply voltage.

  A general band gap type reference voltage generation circuit and a constant current generation circuit will be described with reference to FIGS. FIG. 4 is a circuit diagram showing a general band gap type reference voltage generating circuit. FIG. 5 is a circuit diagram showing a general constant current generating circuit.

=== Configuration of Band Gap Type Reference Voltage Generation Circuit ===
In FIG. 4, a diode-connected (base-collector short circuit) NPN transistor Q1 and NPN transistor Q2 constitute a current mirror circuit. The emitter of transistor Q1 is then directly grounded, while the emitter of transistor Q2 is grounded through resistor R3. The base of the NPN transistor Q3 is connected to the collector of the transistor Q2, and the emitter is grounded. Further, resistors R1 and R2 are connected to the collectors of the transistors Q1 and Q2, respectively. The transistors Q1, Q2, and Q3 and the resistors R1, R2, and R3 constitute a reference voltage generation unit.

  The resistor R4 and the diodes D1 and D2 are connected in series between the power supply voltage VCC and the ground, and a constant voltage is generated at the connection point between the resistor R4 and the diode D1. The NPN transistor Q9 operates when this constant voltage is applied to the base, and stops operating after the reference voltage generator is activated. The emitter of the transistor Q9 is connected to a common connection point on one end side of the resistors R1 and R2. The NPN transistor Q4 is connected in parallel with the transistor Q9 and operates complementarily to the transistor Q9 as will be described later, and its base is connected to the collector of the transistor Q3. Further, the NPN transistor Q10 has a base connected to the base of the transistor Q4, a collector connected to the power supply voltage VCC, and an emitter grounded through a resistor R7. The emitter of the transistor Q10 serves as a terminal for outputting the reference voltage VREF. That is, the transistor Q10 has a buffer function for outputting the reference voltage VREF.

  In the reference voltage generator, it is necessary to make the collector currents of the transistors Q1 and Q3 equal to generate a reference voltage that is not affected by temperature changes. Therefore, when a current mirror circuit is used as a supply source of the collector current, a current mirror circuit composed of PNP transistors Q5 and Q6 and a current mirror circuit composed of PNP transistors Q7 and Q8 are used. Specifically, the emitter of transistor Q5 is connected to power supply voltage VCC via resistor R5, and the emitter of transistor Q6 on the diode-connected side is connected to power supply voltage VCC via resistor R6. Further, the emitter of transistor Q7 on the diode-connected side is connected to the collector of transistor Q5, and the collector of transistor Q7 is connected to the collectors of transistors Q4 and Q9, while the emitter of transistor Q8 is connected to the collector of transistor Q6. The collector of the transistor Q8 is connected to the bases of the transistors Q4 and Q10. That is, the current mirror circuit composed of the transistors Q5 and Q6 and the current mirror circuit composed of the transistors Q7 and Q8 are the same as the transistor Q8 (Q5) on the side where the diode-connected transistor Q6 (Q7) is not diode-connected. It is a two-stage current mirror circuit connected in series. As a result, the influence of the base currents of the transistors Q5 and Q6 can be corrected by the transistors Q7 and Q8, and an appropriate current can be supplied to the reference voltage generator.

=== Operation of Band Gap Type Reference Voltage Generation Circuit ===
First, an operation for generating the voltage VREF ′ having no temperature dependency will be described. The output current flowing through transistor Q2 is set to be smaller than the output current flowing through transistor Q1. Therefore, for example, the current density of the transistor Q2 is set to about 1/10 of that of the transistor Q1. Then, the base-emitter voltage of the transistor Q1 becomes larger than the base-emitter voltage of the transistor Q2, and ΔVBE is generated at both ends of the resistor R3. At the same time, an amplified voltage of ΔVBE · R2 / R3 is generated at both ends of the resistor R2 serving as a collector load of the transistor Q2 (however, R2 and R3 represented by mathematical expressions are resistance values of the resistors R2 and R3). . Accordingly, the voltage VREF ′ generated at one end of the resistors R1 and R2 (emitters of the transistors Q4 and Q9) is the sum of the base-emitter voltage VBE of the transistor Q3 and the amplified voltage ΔVBE · R2 / R3 of the transistor Q2. . Here, VBE has a negative temperature coefficient, and ΔVBE · R2 / R3 has a positive temperature coefficient. Therefore, if the resistance values of the resistors R2 and R3 are appropriately selected, the amplified voltage ΔVBE · R2 / R3 is obtained by inverting and amplifying ΔVBE, so that the voltage VREF ′ is not affected by the temperature change. A value can be generated. In particular, when a band gap type reference voltage generating circuit is configured in a semiconductor integrated circuit, when the sum of VBE and ΔVBE · R2 / R3 becomes the silicon energy gap voltage (about 1.2 V), the voltage VREF ′ Is not affected by temperature changes.

  When the power supply voltage VCC is turned on, an added voltage (for example, 1.4 V) of forward voltages of the diodes D1 and D2 is generated at the base of the transistor Q9. At this time, since the voltage VREF 'has not yet been generated, the transistor Q9 operates, and accordingly, the transistors Q5, Q6, Q7, and Q8 constituting the current mirror circuit also operate. As a result, the collector current of the transistor Q7 is supplied to the reference voltage generator through the transistor Q9, and the voltage VREF ′ is generated. As the transistor Q3 operates, the transistor Q4 starts to operate. At this time, the voltage VREF ′ increases by the base-emitter voltage of the transistor Q4, and further decreases by the base-emitter voltage of the transistor Q10 to become the reference voltage VREF, so that the reference voltage VREF becomes equal to the voltage VREF ′. When the band gap type reference voltage generating circuit operates, the base voltage of the transistor Q4 becomes higher than the base voltage of the transistor Q9, so that the transistor Q4 operates complementarily in place of the transistor Q9. That is, the resistor R4, the diodes D1 and D2, and the transistor Q9 serve as a starting circuit for operating the bandgap reference voltage generation circuit. Thus, the reference voltage VREF that is not affected by the power supply voltage VCC and the temperature change is continuously generated.

=== Configuration of Constant Current Generation Circuit ===
In FIG. 5, in the error amplifier EAMP, a predetermined reference voltage VREF is applied to the + (non-inverting) input terminal, and a detection voltage generated at both ends of the detection resistor R101 is applied to the − (inverting input) terminal. An output voltage corresponding to the difference between the voltage VREF and the detection voltage is generated. That is, the error amplifier EAMP outputs a constant voltage at a predetermined level when the error between the voltages applied to the + terminal and the − terminal becomes zero. For example, a bandgap type reference voltage generation circuit shown in FIG. 4 can be used as the supply source of the reference voltage VREF. The NPN transistor Q101 operates when the output voltage from the error amplifier EAMP is applied to the base. The emitter of this transistor Q101 is grounded via a detection resistor R101. PNP transistor Q102 has an emitter connected to power supply voltage VCC via resistor R102, and a collector connected to the collector of transistor Q101. The PNP transistor Q103 has an emitter connected to the power supply voltage VCC via the resistor R103, and a base connected to the base of the transistor Q102. The collector of the transistor Q103 is a terminal that outputs a constant current for operating the subsequent circuit. The PNP transistor Q104 has an emitter commonly connected to the bases of the transistors Q102 and Q103, a base connected to the collector of the transistor Q102, and a collector grounded. The transistors Q102, Q103, and Q104 constitute a current mirror circuit.

=== Operation of Constant Current Generation Circuit ===
First, the power supply voltage VCC is turned on. For example, when the reference voltage VREF is generated from the power supply voltage VCC, the reference voltage VREF at a predetermined level is generated. The transistor Q101 is biased according to the output voltage from the error amplifier EAMP at this time. On the other hand, when the power supply voltage VCC is turned on, the transistor Q102 operates, and the collector current of the transistor Q102 flows to the detection resistor R101 via the transistor Q101 in a predetermined bias state. As a result, the error amplifier EAMP receives the reference voltage VREF and the detection voltage generated at both ends of the detection resistor R101, outputs an output voltage corresponding to the difference between the two voltages, and outputs a transistor in a bias state corresponding to the output voltage. Q101 will operate. That is, the loop formed to apply the voltage across the detection resistor R101 to the error amplifier EAMP is a negative feedback loop, and the error amplifier EAMP biases the transistor Q101 so that the voltage applied to the negative terminal becomes equal to the reference voltage VREF. Will be. As a result, the output voltage of the error amplifier EAMP is stable in a state where the same voltage as the reference voltage VREF is generated at both ends of the detection resistor R101. In other words, the bias state of the transistor Q101 is stable, that is, from the collector of the transistor Q103. A constant current will be supplied.
JP-A-6-151705

  However, in the case of the band gap type reference voltage generating circuit of FIG. 4, when the reference voltage VREF = 1.2V, the emitter potential of the transistor Q4 = 1.2V, the collector-emitter voltage of the transistor Q4 = about 0.3V, Since the voltage from VCC to the collector of the transistor Q7 is about 1.5V (including a voltage drop due to the resistor R6), the power supply voltage VCC is about 1.2V + 0.3 + 1.5V = 3V. Necessary.

  In the case of the constant current generating circuit of FIG. 5, when the reference voltage VREF = 1.2V, the detection voltage at both ends of the detection resistor R101 = 1.2V, the collector-emitter voltage of the transistor Q101 = about 0.3V, the transistor Since the base-emitter voltage of Q102 and Q104 is about 0.7V, the power supply voltage VCC is (1.2 + 0.3 + 0.7 + 0.7) V = 2.9V even if the voltage drop of the resistor R102 is taken into consideration. A larger power supply voltage of about 3V is required.

  In any case, since the operation is incomplete at a low voltage of less than 3 V, for example, if the circuits of FIGS. 4 and 5 are used in a portable electronic device, the power consumption is large and the battery life is short. There was a problem of becoming. For this reason, as a band gap type reference voltage generation circuit and a constant current generation circuit, a circuit that can operate normally with a low power supply voltage lower than 3V is required.

  Therefore, an object of the present invention is to provide a low voltage operation circuit that effectively operates a band gap type reference voltage generation circuit and a constant current generation circuit.

  An invention for solving the above-described problems includes an error amplifier that generates an output voltage corresponding to a difference between a reference voltage and a voltage across the detection resistor, and an error amplifier that is connected in series with the detection resistor and that corresponds to the output voltage of the error amplifier A first transistor that operates, a second transistor connected in series with the first transistor, a third transistor in which the second transistor and a control electrode are commonly connected, a control electrode of the second transistor, and the first transistor A plurality of fourth transistors having a potential difference between the transistor and the series connection portion of the second transistors equal to or less than a predetermined value, wherein the second transistor, the third transistor, and the plurality of fourth transistors are current mirrors. A low voltage operation circuit is characterized by constituting a circuit.

  Further, a low voltage operation circuit for operating a bandgap reference voltage generation circuit having a current mirror circuit and an output transistor to which an output current of the current mirror circuit is supplied, the diode constituting the current mirror circuit A first transistor connected in series with one of the connected transistors; a second transistor connected in series with the output transistor; and a common connection between the first transistor and a control electrode; and a control electrode of the first transistor And a plurality of third transistors whose potential difference between the first transistor and the electrode on the one transistor side is a predetermined value or less, the first transistor, the second transistor, and the plurality of first transistors The three transistors constitute a current mirror circuit and are a low voltage operation circuit.

  According to the present invention, a circuit that generates a reference voltage and a constant current can be effectively driven by a low voltage power supply.

  At least the following matters will become apparent from the description of this specification and the accompanying drawings.

=== First Embodiment ===
A low voltage generating circuit according to the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of a first embodiment of a low voltage generating circuit according to the present invention, which is applied to a band gap type reference voltage generating circuit. In FIG. 1, the same components as those in FIG. 4 are denoted by the same reference numerals.

<<< Circuit configuration >>>
In FIG. 1, the NPN transistor Q1 and the NPN transistor Q2 that are diode-connected (the base and the collector are short-circuited) constitute a current mirror circuit. The emitter of transistor Q1 is then directly grounded, while the emitter of transistor Q2 is grounded through resistor R3. The base of the NPN transistor Q3 (output transistor) is connected to the collector of the transistor Q2 serving as the output of the current mirror circuit, and the emitter is grounded. Further, resistors R1 and R2 are connected to the collectors of the transistors Q1 and Q2, respectively. The transistors Q1, Q2, Q3 and the resistors R1, R2, R3 surrounded by the alternate long and short dash line constitute a band gap type reference voltage generation circuit BG.

  The resistor R4 and the diodes D1 and D2 are connected in series between the power supply voltage VCC and the ground, and a first constant voltage different from each other at a connection point between the resistor R4 and the diode D1 and a connection point between the diodes D1 and D2. A second constant voltage is generated. The NPN transistor Q9 operates when the first constant voltage is applied to the base, and stops operating after the band gap type reference voltage generation circuit BG is activated. The emitter of the transistor Q9 is connected to a common connection point on one end side of the resistors R1 and R2. The NPN transistor Q4 is connected in parallel with the transistor Q9 and operates complementarily to the transistor Q9 as will be described later, and its base is connected to the collector of the transistor Q3. Further, the NPN transistor Q10 has a base connected to the base of the transistor Q4, a collector connected to the power supply voltage VCC, and an emitter grounded through a resistor R7. The emitter of the transistor Q10 serves as a terminal for outputting the reference voltage VREF. That is, the transistor Q10 has a buffer function for outputting the reference voltage VREF.

  In the band gap type reference voltage generation circuit BG, it is necessary to make the collector currents of the transistors Q1 and Q3 equal in order to generate the reference voltage VREF that is not affected by the temperature change. Therefore, when a current mirror circuit is used as the collector current supply source, the error between the output current of the diode-connected transistor and the output current of the non-diode-connected transistor is required to be extremely small. The

  Therefore, a current mirror circuit composed of a PNP transistor Q201 (first transistor), a PNP transistor Q202 (second transistor), an NPN transistor Q203 (third transistor), and a PNP transistor Q204 (third transistor) is applied. Specifically, the emitter of transistor Q201 is connected to power supply voltage VCC via resistor R201, and its collector is connected to the common collector of transistors Q4 and Q9. The emitter of transistor Q202 is connected to power supply voltage VCC via resistor R202, and its collector is connected to the collector of transistor Q3 (bases of transistors Q4 and Q10). Further, the bases (control electrodes) of the transistors Q201 and Q202 are commonly connected. The base of transistor Q203 is connected to the collector of transistor Q201, and the collector is connected to power supply voltage VCC. Further, the base of the transistor Q204 is connected to the emitter of the transistor Q203, the emitter is connected to the common base of the transistors Q201 and Q202, and the collector is grounded. A second constant voltage is applied to the base of the NPN transistor Q205, its collector is connected to the base of the transistor Q204, and its emitter is grounded. The resistor R4, the diodes D1 and D2, and the transistor Q205 constitute a constant current circuit.

  Here, when the resistance value of the resistor R203 is negligible as compared with the base-emitter voltage of the transistors Q203 and Q204, when comparing the base voltage of the transistors Q201 and Q202 and the collector voltage of the transistor Q201, the transistors Q201 and Q202 are compared. The base voltage of the transistor Q204 decreases by the base-emitter voltage of the transistor Q204 and increases by the base-emitter voltage of the transistor Q203, whereby the collector voltage of the transistor Q201 is obtained. That is, the base voltage of the transistors Q201 and Q202 and the collector voltage of the transistor Q201 are set approximately equal by the connection of the transistors Q203 and Q204. In other words, the potential difference between the base voltages of the transistors Q201 and Q202 and the collector voltage of the transistor Q201 is almost zero (a predetermined value or less).

<<< Circuit Operation >>>
First, an operation for generating the voltage VREF ′ having no temperature dependency will be described. The output current flowing through the transistor Q2 is set to be smaller than the output current flowing through the transistor Q1 due to the emitter resistance value determined by the resistor R3. For example, the current density of the transistor Q2 is set to about 1/10 of that of the transistor Q1. Then, the base-emitter voltage of the transistor Q1 becomes larger than the base-emitter voltage of the transistor Q2, and ΔVBE is generated at both ends of the resistor R3. At the same time, an amplified voltage of ΔVBE · R2 / R3 is generated at both ends of the resistor R2 serving as a collector load of the transistor Q2 (however, R2 and R3 represented by mathematical expressions are resistance values of the resistors R2 and R3). . Accordingly, the voltage VREF ′ generated at one end of the resistors R1 and R2 (emitters of the transistors Q4 and Q9) is the sum of the base-emitter voltage VBE of the transistor Q3 and the amplified voltage ΔVBE · R2 / R3 of the transistor Q2. . Here, VBE has a negative temperature coefficient, and ΔVBE · R2 / R3 has a positive temperature coefficient. Therefore, if the resistance values of the resistors R2 and R3 are appropriately selected, the amplified voltage ΔVBE · R2 / R3 is obtained by inverting and amplifying ΔVBE, so that the voltage VREF ′ is not affected by the temperature change. A value can be generated. In particular, when a band gap type reference voltage generating circuit is configured in a semiconductor integrated circuit, when the sum of VBE and ΔVBE · R2 / R3 becomes the silicon energy gap voltage (about 1.2 V), the voltage VREF ′ Is not affected by temperature changes.

  When the power supply voltage VCC is turned on, a first constant voltage (for example, 1.4 V) obtained by adding the forward voltages of the diodes D1 and D2 is applied to the base of the transistor Q9. At this time, since the voltage VREF 'has not yet been generated, the transistor Q9 operates because its emitter voltage is lowered to near ground, and accordingly, the transistors Q201, Q202, Q203 constituting the current mirror circuit are operated. , Q204 also operates. On the other hand, a second constant voltage lower than the first constant voltage is applied to the base of the transistor Q205, and the transistor Q205 is driven with a constant bias. As a result, the base current of the transistor Q204 becomes constant, and the transistor Q204 draws a constant base current as a collector current from the bases of the transistors Q201 and Q202. Therefore, the transistors Q201 and Q202 are driven with a constant bias. Here, the emitter current of the transistor Q204 is compared with the base current of the transistor Q203. When the current amplification factors of the transistors Q201, Q203, and Q204 are hFE, the base current of the transistor Q203 is about (1 / hFE) squared compared to the emitter current of the transistor Q204. In other words, the transistor Q203 operates by setting a base current that is approximately the square of (1 / hFE) with respect to the emitter current of the transistor Q204. That is, the amount of current flowing from the collector of the transistor Q201 to the base of the transistor Q203 can be set to a very small current value so that it can be ignored as compared with the collector current of the transistor Q201. As a result, a collector current with a very small error in the current mirror ratio of the transistors Q201 and Q202 can be obtained with certainty.

  The collector current of the transistor Q201 is supplied to the band gap type reference voltage generation circuit BG through the transistor Q9, and the voltage VREF ′ is generated. As the transistor Q3 operates, the transistor Q4 starts to operate. At this time, the voltage VREF ′ increases by the base-emitter voltage of the transistor Q4, and further decreases by the base-emitter voltage of the transistor Q10 to become the reference voltage VREF, so that the reference voltage VREF becomes equal to the voltage VREF ′. When the band gap type reference voltage generating circuit operates, the base voltage of the transistor Q4 becomes higher than the base voltage of the transistor Q9, so that the transistor Q4 operates complementarily in place of the transistor Q9. That is, the resistor R4, the diodes D1 and D2, and the transistor Q9 serve as a starting circuit for operating the bandgap reference voltage generation circuit BG. Thus, when the power supply voltage VCC is in a steady state, the reference voltage VREF that is not affected by the temperature change is continuously generated.

  As described above, by applying the current mirror circuit having the transistors Q201, Q202, Q203, and Q204, the current flowing from the collector of the transistor Q201 to the base of the transistor Q203 is negligible compared to the collector current of the transistor Q201. Since the current value is only about, a substantially equal collector current can be obtained from the collectors of the transistors Q201 and Q202. Therefore, it is possible to reliably obtain the reference voltage VREF that does not depend on the temperature characteristics.

  Further, by adopting the circuit shown in FIG. 1, when the reference voltage VREF = 1.2V, the emitter voltage of the transistor Q4 = 1.2V, the collector-emitter voltage of the transistor Q4 = about 0.3V, the transistor Q201 Therefore, the added voltage is (1.2 + 0.3 + 0.3) V = 1.8V. Considering the resistance value of the resistor R201, it is sufficient to prepare a power supply voltage VCC of about 2V. Therefore, the low voltage operation circuit that operates the band gap type reference voltage generation circuit BG of FIG. 1 can normally output the reference voltage VREF if the power supply voltage VCC of about 2V is prepared. In other words, it is possible to provide a circuit capable of extending the battery life as a band gap type reference voltage generation circuit used for operating a portable device. Further, the low voltage operation circuit of FIG. 1 can be an integrated circuit.

=== Second Embodiment ===
The low voltage generation circuit according to the present invention will be described with reference to FIG. FIG. 2 is a circuit diagram of a second embodiment of a low voltage generation circuit according to the present invention, which is applied to a constant current generation circuit. In FIG. 2, the same components as those in FIG.

<<< Circuit configuration >>>
In FIG. 2, the error amplifier EAMP has a predetermined reference voltage VREF applied to the + (non-inverting) input terminal and a detection voltage generated across the detection resistor R101 to the − (inverting input) terminal. An output voltage corresponding to the difference between the voltage VREF and the detection voltage is generated. That is, the error amplifier EAMP outputs a constant voltage at a predetermined level when the error between the voltages applied to the + terminal and the − terminal becomes zero. As a supply source of the reference voltage VREF, for example, a low voltage operation circuit shown in FIG. 1 can be used. The NPN transistor Q101 (first transistor) operates when the output voltage from the error amplifier EAMP is applied to the base. The emitter of this transistor Q101 is grounded via a detection resistor R101. On the collector side of the transistor Q101, a current mirror circuit composed of a PNP transistor Q102 (second transistor), a PNP transistor Q103 (third transistor), an NPN transistor Q301 (fourth transistor), and a PNP transistor (fourth transistor). Is provided. Specifically, transistor Q102 has an emitter connected to power supply voltage VCC via resistor R102, and a collector connected to the collector of transistor Q101. The PNP transistor Q103 has an emitter connected to the power supply voltage VCC via the resistor R103, and a base commonly connected to the base of the transistor Q102. The collector of the transistor Q103 is a terminal that outputs a constant current for operating the subsequent circuit. The base of the transistor Q301 is connected to the collector of the transistor Q102, the collector is connected to the power supply voltage VCC, and the emitter is grounded via the resistor R301. Further, the base of the transistor Q302 is connected to the emitter of the transistor Q301, its emitter is connected to the common base of the transistors Q102 and Q103, and its collector is grounded via the resistor R302. Here, when the base voltages of the transistors Q102 and Q103 are compared with the collector voltage of the transistor Q102, the base voltages of the transistors Q102 and Q103 decrease by the base-emitter voltage of the transistor Q302 and increase by the base-emitter voltage of the transistor Q301. Thus, the collector voltage of the transistor Q102 is obtained. That is, the base voltage of the transistors Q102 and Q103 and the collector voltage of the transistor Q102 are set equal by the connection of the transistors Q301 and Q302. In other words, the potential difference between the base voltages of the transistors Q102 and Q103 and the collector voltage of the transistor Q102 is zero (a predetermined value or less).

<<< Circuit Operation >>>
First, the power supply voltage VCC is turned on. For example, when the reference voltage VREF is generated from the power supply voltage VCC, the reference voltage VREF having a predetermined level (for example, 1.2 V) is generated. The transistor Q101 is biased according to the output voltage from the error amplifier EAMP at this time. On the other hand, when the power supply voltage VCC is turned on, the transistor Q102 operates, and the collector current of the transistor Q102 flows to the detection resistor R101 via the transistor Q101 in a predetermined bias state. As a result, the error amplifier EAMP receives the reference voltage VREF and the detection voltage generated at both ends of the detection resistor R101, outputs an output voltage corresponding to the difference between the two voltages, and outputs a transistor in a bias state corresponding to the output voltage. Q101 will operate. That is, the loop formed to apply the voltage across the detection resistor R101 to the error amplifier EAMP is a negative feedback loop, and the error amplifier EAMP biases the transistor Q101 so that the voltage applied to the negative terminal becomes equal to the reference voltage VREF. Will be. As a result, the output voltage of the error amplifier EAMP is stable in a state where the same voltage as the reference voltage VREF is generated at both ends of the detection resistor R101. In other words, the bias state of the transistor Q101 is stable, that is, from the collector of the transistor Q103. A constant current will be supplied.

  Here, the emitter current of the transistor Q302 is compared with the base current of the transistor Q301. When the current amplification factors of the transistors Q102, Q301, and Q302 are hFE, the base current of the transistor Q301 is about (1 / hFE) squared compared to the emitter current of the transistor Q302. In other words, the transistor Q301 operates by setting a base current that is approximately the square of (1 / hFE) with respect to the emitter current of the transistor Q302. That is, the amount of current flowing from the collector of the transistor Q102 to the base of the transistor Q301 can be set to an extremely small current value that can be ignored as compared with the collector current of the transistor Q102. Thereby, it is possible to reliably obtain a collector current having a very small error in the current mirror ratio according to the sizes of the transistors Q201 and Q202. Thereby, a constant current according to the current mirror ratio can be supplied from the collector of the transistor Q103.

  Further, the transistors Q102, Q301, and Q302 constituting the current mirror circuit can be constituted by low-saturation transistors with low on-resistance. Thus, when the reference voltage VREF = 1.2V, the detection voltage generated at both ends of the detection resistor R101 = 1.2V, the collector-emitter voltage of the transistor Q101 = about 0.3V, and the collector-emitter voltage of the transistor Q102 = About 0.3V, so the added voltage is (1.2 + 0.3 + 0.3) V = 1.8V. Considering the resistance value of the resistor R102, it is sufficient to prepare the power supply voltage VCC of about 2V. Therefore, the low voltage operation circuit for generating a constant current in FIG. 2 can normally generate a constant current if a power supply voltage VCC of about 2V is prepared. In other words, a circuit capable of extending the battery life can be provided as a constant current generating circuit used for operating the portable device. Further, by adopting the circuit configuration of FIG. 2, it is possible to ensure a sufficient driving capability of the transistor Q103 that outputs a constant current while the power supply voltage VCC is relatively low, such as about 2V.

  Further, the low voltage operation circuit of FIG. 2 can be an integrated circuit. In particular, when the reference voltage VREF output from the low voltage operation circuit of FIG. 1 is used as the reference voltage VREF of the low voltage operation circuit of FIG. 2, the same power supply voltage VCC can be used. It becomes easy to form the voltage operation circuit on the same chip.

=== Third Embodiment ===
A low voltage generating circuit according to the present invention will be described with reference to FIG. FIG. 3 is a third embodiment of the low voltage generation circuit according to the present invention, and is another circuit diagram when applied to a constant current generation circuit. In FIG. 3, the same components as those in FIG. 2 are denoted by the same reference numerals.

<<< Circuit configuration >>>
In FIG. 3, a predetermined reference voltage VREF is applied to the + (non-inverted) input terminal of the error amplifier EAMP, and the voltage across the detection resistor R101 is applied to the P-N transistor Q401 (fifth input) at its − (inverted input) terminal. A voltage increased by the voltage between the base and the emitter of the transistor) is applied as the detection voltage. The error amplifier EAMP generates an output voltage corresponding to the difference between the applied voltages at the + terminal and the − terminal. That is, the error amplifier EAMP outputs a constant voltage at a predetermined level when the error between the voltages applied to the + terminal and the − terminal becomes zero. The transistor Q401 has a base connected to one end on the non-ground side of the detection resistor R101, an emitter connected to the power supply voltage VCC via the resistor R401, and a collector grounded. Further, the emitter of the transistor Q401 is connected to the negative terminal of the error amplifier EAMP. As a supply source of the reference voltage VREF, for example, a low voltage operation circuit shown in FIG. 1 can be used. The NPN transistor Q101 (first transistor) operates when the output voltage from the error amplifier EAMP is applied to the base. The emitter of this transistor Q101 is grounded via a detection resistor R101. On the collector side of the transistor Q101, a current mirror circuit composed of a PNP transistor Q102 (second transistor), a PNP transistor Q103 (third transistor), an NPN transistor Q301 (fourth transistor), and a PNP transistor (fourth transistor). Is provided. Specifically, transistor Q102 has an emitter connected to power supply voltage VCC via resistor R102, and a collector connected to the collector of transistor Q101. The PNP transistor Q103 has an emitter connected to the power supply voltage VCC via the resistor R103, and a base commonly connected to the base of the transistor Q102. The collector of the transistor Q103 is a terminal that outputs a constant current for operating the subsequent circuit. The base of the transistor Q301 is connected to the collector of the transistor Q102, the collector is connected to the power supply voltage VCC, and the emitter is grounded via the resistor R301. Further, the base of the transistor Q302 is connected to the emitter of the transistor Q301, its emitter is connected to the common base of the transistors Q102 and Q103, and its collector is grounded via the resistor R302. Here, when the base voltages of the transistors Q102 and Q103 are compared with the collector voltage of the transistor Q102, the base voltages of the transistors Q102 and Q103 decrease by the base-emitter voltage of the transistor Q302 and increase by the base-emitter voltage of the transistor Q301. Thus, the collector voltage of the transistor Q102 is obtained. That is, the base voltage of the transistors Q102 and Q103 and the collector voltage of the transistor Q102 are set equal by the connection of the transistors Q301 and Q302. In other words, the potential difference between the base voltages of the transistors Q102 and Q103 and the collector voltage of the transistor Q102 is zero (a predetermined value or less).

<<< Circuit Operation >>>
First, the power supply voltage VCC is turned on. For example, when the reference voltage VREF is generated from the power supply voltage VCC, the reference voltage VREF having a predetermined level (for example, 1.2 V) is generated. The transistor Q101 is biased according to the output voltage from the error amplifier EAMP at this time. On the other hand, when the power supply voltage VCC is turned on, the transistor Q102 operates, and the collector current of the transistor Q102 flows to the detection resistor R101 via the transistor Q101 in a predetermined bias state. As a result, the error amplifier EAMP receives the reference voltage VREF, the sum voltage (detection voltage) of the voltage across the detection resistor R101 and the base-emitter voltage of the transistor Q401, and outputs an output voltage corresponding to the difference between the two voltages. The transistor Q101 operates in a bias state corresponding to the output voltage. That is, the loop formed to apply the addition voltage to the error amplifier EAMP is a negative feedback loop, and the error amplifier EAMP biases the transistor Q101 so that the voltage applied to the negative terminal becomes equal to the reference voltage VREF. It becomes. Thus, the output voltage of the error amplifier EAMP is stabilized in a state where the same voltage as the voltage obtained by subtracting the base-emitter voltage of the transistor Q401 from the reference voltage VREF is generated at both ends of the detection resistor R101, in other words, the bias of the transistor Q101. The state is stable, that is, a constant current is supplied from the collector of the transistor Q103.

  Here, the emitter current of the transistor Q302 is compared with the base current of the transistor Q301. When the current amplification factors of the transistors Q102, Q301, and Q302 are hFE, the base current of the transistor Q301 is about (1 / hFE) squared compared to the emitter current of the transistor Q302. In other words, the transistor Q301 operates by setting a base current that is approximately the square of (1 / hFE) with respect to the emitter current of the transistor Q302. That is, the amount of current flowing from the collector of the transistor Q102 to the base of the transistor Q301 can be set to an extremely small current value that can be ignored as compared with the collector current of the transistor Q102. Thereby, it is possible to reliably obtain a collector current having a very small error in the current mirror ratio according to the sizes of the transistors Q201 and Q202. Thereby, a constant current according to the current mirror ratio can be supplied from the collector of the transistor Q103.

  Further, the transistors Q102, Q301, and Q302 constituting the current mirror circuit can be constituted by low-saturation transistors with low on-resistance. Thus, when the reference voltage VREF = 1.2V, the detection voltage generated at both ends of the detection resistor R101 = (1.2−0.7) V = 0.5V, the collector-emitter voltage of the transistor Q101 = about Since the voltage between the collector and the emitter of the transistor Q102 is about 0.3V, this added voltage is (0.5 + 0.3 + 0.3) V = 1.1V. Considering the resistance value of the resistor R102, it is sufficient to prepare the power supply voltage VCC of about 1.5V. Therefore, the low voltage operation circuit for generating the constant current of FIG. 3 can normally generate the constant current if the power supply voltage VCC of about 1.5V is prepared. In other words, it is possible to provide a circuit that can significantly increase the battery life as compared with FIG. 2 as a constant current generation circuit used for operating the portable device. Further, by adopting the circuit configuration of FIG. 3, it is possible to ensure a sufficient driving capability of the transistor Q103 that outputs a constant current while the power supply voltage VCC is about 1.5 V lower than that of FIG. Become. Furthermore, the low voltage operation circuit of FIG. 3 may be an integrated circuit.

=== Summary ===
As described above, the error amplifier EAMP that generates an output voltage corresponding to the difference between the reference voltage VREF and the voltage across the detection resistor R101 and the detection resistor R101 are connected in series and operate according to the output voltage of the error amplifier EAMP. A transistor Q101 connected in series, a transistor Q102 connected in series with the transistor Q101, a transistor Q103 with a base connected in common to the transistor Q102, a base voltage of the transistor Q102, and a voltage at a series connection portion of the transistor Q101 and the transistor Q102. The transistors Q301 and Q302 are made equal, and the transistors Q102, Q103, Q301, and Q302 constitute a current mirror circuit. As a result, the power supply voltage VCC used for a circuit that generates a constant current can be lowered.

  In addition, the transistors Q301 and Q302 have a current that flows from the series connection portion of the transistors Q101 and Q102 to the base of the transistor Q301 to the square of (1 / hFE) with respect to the current that flows through the control electrodes of the transistors Q102 and Q103. The transistor Q101 and the transistor Q102 are connected in series and the common base of the transistors Q102 and Q103 is connected. Thereby, the error of the collector current output from the transistors Q102 and Q103 in the current mirror circuit can be extremely reduced. Accordingly, it is possible to generate an accurate constant current to be supplied to the subsequent circuit.

  Further, by employing the circuit configured in FIG. 2 and FIG. 3, it is possible to sufficiently secure the driving capability of the transistor Q103 that outputs a constant current while the power supply voltage VCC is low.

  In addition, the transistor Q401 further lowers the voltage across the detection resistor R101 by the forward voltage. The error amplifier EAMP includes the reference voltage VREF and the transistor Q401 that rises from the voltage across the detection resistor R101 by the forward voltage. An output voltage corresponding to the difference between the output voltage and the output voltage is generated. Thus, it is possible to provide a low voltage operation circuit in which the power supply voltage VCC is further reduced as compared with FIG.

  A low-voltage operation circuit for operating a bandgap reference voltage generation circuit BG having a current mirror circuit (Q1, Q2) and an output transistor Q3 to which an output current of the current mirror circuit is supplied, Transistor Q201 connected in series with one diode-connected transistor Q1 constituting the current mirror circuit, transistor Q3 connected in series with transistor Q3, and commonly connected to the base of transistor Q201 and the base of transistor Q201 Transistors Q203 and Q204 having substantially the same voltage and collector voltage are provided. The transistors Q201, Q202, Q203, and Q204 constitute a current mirror circuit. As a result, the power supply voltage VCC of the bandgap reference voltage generation circuit that generates the reference voltage VREF that does not depend on the temperature change can be lowered.

  Further, the transistors Q203 and Q204 are arranged such that the current flowing from the collector of the transistor Q201 to the base of the transistor Q203 is about (1 / hFE) square of the current flowing through the bases of the transistors Q201 and Q202. It is connected between the collector of Q201 and the common base of transistors Q201 and Q202. Thereby, the error of the collector current output from the transistors Q201 and Q202 constituting the current mirror circuit can be extremely reduced. Therefore, the reference voltage VREF can be reliably generated under the low power supply voltage VCC.

  Further, a constant current circuit for operating the transistors Q203 and Q204 with a constant current is provided. As a result, the transistors Q203 and Q204 can be driven in a constant bias state, and a stable reference voltage VREF can be obtained.

  The low voltage operation circuit according to the present invention has been described above. However, the above description is intended to facilitate understanding of the present invention and does not limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents.

1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows 2nd Embodiment of this invention. It is a circuit diagram which shows 3rd Embodiment of this invention. It is a circuit diagram which shows the conventional band gap type reference voltage generation circuit. It is a circuit diagram which shows the conventional constant current generation circuit.

Explanation of symbols

BG Band gap type reference voltage generation circuit Q201, Q202, Q203, Q204 Current mirror circuit R4, D1, D2, Q205 Constant current circuit Q102, Q103, Q301, Q302 Current mirror circuit EAMP Error amplifier R101 Detection resistor Q401 Fifth transistor

Claims (6)

An error amplifier that generates an output voltage according to the difference between the reference voltage and the voltage across the detection resistor;
A first transistor connected in series with the detection resistor and operating in accordance with an output voltage of the error amplifier;
A second transistor connected in series with the first transistor;
A third transistor having a control electrode connected in common to the second transistor;
A plurality of fourth transistors having a potential difference between a control electrode of the second transistor and a series connection portion of the first transistor and the second transistor equal to or less than a predetermined value;
The low-voltage operation circuit, wherein the second transistor, the third transistor, and the plurality of fourth transistors constitute a current mirror circuit. The plurality of fourth transistors include:
The current flowing from the serial connection of the first transistor and the second transistor is (1 / the current amplification factor of each fourth transistor) with respect to the current flowing through the control electrodes of the second transistor and the third transistor. To be the multiple powers of
2. The low-voltage operation circuit according to claim 1, wherein the low-voltage operation circuit is connected between a series connection portion of the first transistor and the second transistor and a control electrode of the second transistor and the third transistor. . A fifth transistor for reducing the voltage across the detection resistor by a forward voltage;
2. The error amplifier generates an output voltage corresponding to a difference between the reference voltage and an output voltage of the fifth transistor that is increased by a forward voltage from a voltage across the detection resistor. Or the low-voltage operation circuit according to 2; A low voltage operation circuit for operating a bandgap reference voltage generation circuit having a current mirror circuit and an output transistor to which an output current of the current mirror circuit is supplied,
A first transistor connected in series with one diode-connected transistor constituting the current mirror circuit;
A second transistor connected in series with the output transistor and having the first transistor and a control electrode connected in common;
A plurality of third transistors having a potential difference between a control electrode of the first transistor and an electrode on the one transistor side of the first transistor that is equal to or less than a predetermined value;
The low-voltage operation circuit, wherein the first transistor, the second transistor, and the plurality of third transistors constitute a current mirror circuit. The plurality of third transistors include:
The current flowing from the electrode on the one transistor side of the first transistor is (1 / the current amplification factor of each third transistor) with respect to the current flowing through the control electrodes of the first transistor and the second transistor. ) To be a plurality of powers of
5. The low-voltage operation according to claim 4, wherein the low-voltage operation is connected between an electrode on the one transistor side of the first transistor and a control electrode of the first transistor and the second transistor. circuit. 6. The low voltage operation circuit according to claim 4, further comprising a constant current circuit that operates the plurality of third transistors with a constant current.

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