JP2021189477A - Constant current circuit - Google Patents

Abstract

To improve output current accuracy in an operation temperature range by realizing further improvement in a temperature characteristic of an output current.SOLUTION: There are provided a constant current output unit 11, an output reference voltage generation unit 13, and a transconductance amplifier 12. A connection node of resistors R2 and R3 connected in series between a collector and emitter of a transistor QN1 provided to the output reference voltage generation unit 13 is set to be an output section of the output reference voltage, and the output reference voltage is supplied to a non-inverting input end of a differential amplifier AMP1 of the constant current output unit 11. The transconductance amplifier 12 sets an input of a voltage according to a reference voltage Vref2 to a first input section, an input of a voltage according to an emitter voltage of the transistor QN1 to a second input section, and an input of a voltage according to a collector voltage of a transistor QN2 to a third input section, feeds an output voltage according to a voltage difference between a voltage of the first input section and a voltage of the second or third input section to a resistor R5, and generates a correcting voltage to the resistor R5.SELECTED DRAWING: Figure 1

Description

The present invention relates to a constant current circuit.

Conventionally, a constant current circuit that outputs a predetermined constant current has been widely used. As a conventional example of a constant current circuit, for example, there is a circuit that obtains a constant current by converting the voltage of a reference voltage source by a resistor (see Patent Document 1). In this conventional constant current source circuit, a diode or a diode-connected transistor that compensates for the temperature change of the resistor by the forward voltage temperature change thereof is provided in the reference voltage source. In this configuration, a constant current source circuit having no temperature characteristic is realized by giving a compensation voltage characteristic using the temperature characteristic of a diode or a transistor to the temperature characteristic of the resistor.

Japanese Unexamined Patent Publication No. 5-235661

The constant current circuit is extremely useful as a circuit that outputs a constant current regardless of the temperature in the IC, such as a built-in oscillator of a switching power supply or a drive circuit that drives an LED with a constant current. In particular, in an in-vehicle device, the current value is required to be constant in an extremely wide temperature range of, for example, -40 to + 150 ° C. Therefore, further improvement of the temperature characteristics of the constant current circuit is required.

It is an object of the present invention to provide a constant current circuit capable of further improving the temperature characteristics of the output current and improving the output current accuracy in the operating temperature range.

The present invention comprises a differential amplifier, a first resistance element whose one end is connected to the inverting input end of the differential amplifier and whose other end is grounded, and a gate or emitter to which a source or emitter is connected to one end of the first resistance element. A current proportional to the voltage at the non-inverting input end of the differential amplifier includes an output transistor whose base is connected to the output end of the differential amplifier, and a current proportional to the voltage at the non-inverting input end of the differential amplifier reaches the first resistance element via the output transistor. A constant current output unit that obtains a constant current from the drain or collector of the output transistor by a flowing operation, a first reference voltage generation unit that generates a first reference voltage, and a collector are used in the first reference voltage generation unit. The connected first correction transistor, the second resistance element and the third resistance element connected in series between the collector and the emitter of the first correction transistor, and the first correction transistor. A correction resistance element inserted between the base and the collector is included, and the connection node between the second resistance element and the third resistance element is used as an output unit of the output reference voltage, and the differential amplifier is non-inverting. The output reference voltage generator supplied to the input end, the second reference voltage generator that generates the second reference voltage, the base and the collector are short-circuited, the emitter is grounded, and a constant current flows through the collector. A second correction transistor to which a current source is connected is included, and an input of a voltage corresponding to the second reference voltage is input to the first input unit and a voltage corresponding to the emitter voltage of the first correction transistor. Is the second input unit, and the input of the voltage corresponding to the collector voltage of the second correction transistor is the third input unit, the voltage of the first input unit, the voltage of the second input unit, and the second input unit. (3) A transistor conduction amplifier that outputs a current according to a potential difference from the higher voltage of the input unit is provided, and the output current of the transistor conduction amplifier flows through the correction resistance element to flow the correction resistance. Provided to the element is a constant current circuit that generates a correction voltage according to a potential difference between the voltage of the first input unit of the transistor conduction amplifier and the voltage of the second or third input unit.

Further, the present invention is the above-mentioned constant current circuit, in which the output reference voltage generation unit has an NPN-type transistor serving as the first correction transistor, and the emitter of the NPN-type transistor is the transconductance amplifier. A fourth resistance element connected to the second input portion of the NPN transistor, one end connected to the emitter of the NPN transistor and the other end connected to the grounded third resistance element, and a fifth resistance element to be the correction resistance element. To provide a constant current circuit having the above and connecting the base of the NPN transistor to the output section of the transconductance amplifier.

Further, the present invention is the above-mentioned constant current circuit, wherein the transconductance amplifier has third, fourth, and fifth transistors to which emitters are commonly connected, and the base of the third transistor is the base. The base of the first input unit and the fourth transistor is the second input unit, the base of the fifth transistor is the third input unit, and the emitters of the third to fifth transistors are the first current sources. The collectors of the fourth and fifth transistors are connected to each other and connected to the input of the current mirror circuit as the output unit of the transconductance amplifier, and the output of the current mirror circuit is connected to the input of the current mirror circuit. Provided is a constant current circuit connected to the base of the correction transistor of 1.

Further, the present invention is the above-mentioned constant current circuit, in which the fifth transistor is turned on at a temperature lower than the first predetermined temperature and the fourth transistor is turned on at a temperature lower than the first predetermined temperature in the transconductance amplifier. Provided is a constant current circuit that is turned on on a higher temperature side than the second predetermined temperature and supplies a current to the correction resistance element at each on.

Further, the present invention is the above-mentioned constant current circuit, wherein the first current source is the same as the correction resistance element as a resistance element in which the first reference voltage is input as a reference voltage and an output current is passed. It has a sixth resistance element with a temperature coefficient, and the output current value is a current proportional to the value obtained by the product of the ratio of the resistance values of the correction resistance element and the sixth resistance element to the first reference voltage. Provides a constant current circuit with values.

Further, the present invention is the above-mentioned constant current circuit, in which the output reference voltage generation unit includes a PNP-type transistor serving as the first correction transistor and an NPN in which a collector is connected to a collector of the PNP-type transistor. It has a type transistor and a second current source connected to the emitter of the PNP type transistor, the emitter of the NPN type transistor is connected to the second input portion of the transconductance amplifier, and the emitter of the NPN type transistor is connected. A fourth resistance element having one end connected to the ground and the other end grounded, a fifth resistance element inserted between the base and collector of the NPN transistor, and a seventh resistance element serving as the correction resistance element. To provide a constant current circuit having the

According to the present invention, it is possible to correct the temperature fluctuation of the output current due to not only the primary temperature coefficient of the resistance element used in the constant current circuit but also the secondary temperature coefficient, so that the temperature characteristics of the output current can be further improved. It is possible to provide a constant current circuit capable of improving the output current accuracy in the entire operating temperature range.

It is a circuit diagram which shows the structure of the constant current circuit of 1st Embodiment. It is a characteristic diagram which shows an example of the temperature characteristic of each part in the constant current circuit of an embodiment. It is a characteristic diagram which shows an example of the temperature characteristic of the output current in the constant current circuit of an embodiment. It is a circuit diagram which shows the structure of the constant current circuit of 2nd Embodiment. It is a circuit diagram which shows the structure of the constant current circuit of 3rd Embodiment. It is a circuit diagram which shows the structure of the constant current circuit of the comparative example. It is a characteristic diagram which shows the temperature characteristic of the output current in the constant current circuit of the comparative example.

Hereinafter, an embodiment in which the constant current circuit according to the present invention is specifically disclosed (hereinafter, referred to as “the present embodiment”) will be described in detail with reference to the drawings.

(Background to this embodiment)
Generally, a diffusion resistor is used as a resistance element built in an electronic circuit device such as an IC. Therefore, the electronic circuit device constituting the constant current circuit often has a positive temperature coefficient with respect to the temperature. In a constant current circuit, in order to obtain a constant current with respect to temperature, a circuit configuration for canceling the temperature coefficient of the resistance element is required.

As a comparative example, a function of canceling the temperature coefficient of the resistance element will be described using a constant current circuit as shown in FIG. 4 of Patent Document 1.

FIG. 6 is a circuit diagram showing the configuration of a constant current circuit of a comparative example. In the constant current circuit of the comparative example, the relationship between the resistance value of the resistor R51 as a resistance element and the temperature of the base-emitter potential difference Vbe of the NPN type transistor QN51 is as shown in the following equations (1) and (2). Suppose. In the present specification, the resistance value of the resistance RX (X is an arbitrary integer) is represented by RX.

R51 = R51 ₂₅ · {1 + Tc1 (T-298)} ... (1)
Vbe = Vbe ₂₅ + α ・ (T-298)… (2)

In the above equation, _{the resistance value of R51 at R51 25} : 25 ° C., Tc1: primary temperature coefficient of resistance, T: Kelvin temperature, Vbe ₂₅ : base-emitter potential difference of QN51 at 25 ° C., α: Vbe temperature. Fluctuation (-2 mV / ° C). Here, it is assumed that the primary temperature coefficient Tc1 of the resistance is positive. Moreover, the temperature coefficient of the second order or higher is ignored.

Assuming that the resistance values of the resistors R52 and R53 are sufficiently larger than the resistance value of the resistor R54 and the collector current of the transistor QN51 is substantially equal to the current flowing through the resistor R54, the node A shown by the point A in the figure 6 The voltage Va is as shown in the following equation (3).

Va = Vref1-Vbe · (1-N) ... (3)

In equation (3), it is the first reference voltage by Vref1: reference voltage source Vref1. Further, N is the ratio of the resistance values of the resistors R53 and the resistors R52 + R53, and is as shown in the following equation (4).

N = R53 / (R52 + R53) ... (4)

Using the voltage Va of the node A as the output reference voltage, the differential amplifier AMP51 and the NchMOS type transistor MN51 generate the same voltage as the voltage Va across the resistor R51. At this time, the output current IOUT, which is the drain current of the transistor MN51, is expressed by the following equation (5).

IOUT = {Vref1-Vbe · (1-N)} / R51 ... (5)

When the output current IOUT is differentiated with respect to the temperature T using the above equations (1) and (2), the following equation (6) is obtained.

Here, the condition of the coefficient N for making the molecule of the equation (6) zero can be obtained as the following equations (7) and (8).

By adjusting the resistance values of the resistance R52 and the resistance R53 as in the equation (8), the temperature coefficient of the voltage Va of the node A becomes equal to the temperature coefficient of the resistance R51, and the temperature fluctuation of the output current IOUT is minimized. can do.

As an example, in the case of a bipolar transistor, α is about -2 mV / ° C, Vref1 = 1.25V, Vbe ₂₅ = 0.65V, and the primary temperature coefficient of resistance Tc1 = + 0.0013 [1 / ° C.]. , N = 0.429.

In the above-mentioned equation (1), the temperature coefficient of the second order or higher of the resistor is ignored, but the temperature coefficient of the second order may not be ignored depending on the characteristics of the resistor used for the resistor R51. In particular, in applications where high-precision constant current output is required over a wide temperature range, such as in-vehicle devices, it is necessary to consider a second-order temperature coefficient. When the second-order temperature coefficient of the resistance is included, the equation (1) becomes the following equation (9).

R51 = R51 ₂₅ · {1 + Tc1 (T-298)
+ Tc2 (T-298) ² } ... (9)
In the above equation, Tc2: the secondary temperature coefficient of the resistor.

FIG. 7 is a characteristic diagram showing the temperature characteristics of the output current in the constant current circuit of the comparative example. FIG. 7 shows the relationship between the output current IOUT and the temperature when a resistor element having a positive second-order temperature coefficient is used for the resistor R51. As shown in FIG. 7, on the high temperature side and the low temperature side, the resistance value increases due to the secondary temperature coefficient of the resistance, and the output current IOUT decreases. The temperature coefficient of the resistor is often determined by the manufacturing process of the semiconductor to be used, and there are cases where a resistor having a large secondary temperature coefficient has to be used.

In this embodiment, in view of the above circumstances, a configuration example of a constant current circuit capable of correcting the temperature fluctuation of the output current due to the secondary temperature coefficient of the resistance element to be used and further improving the temperature characteristics is shown.

(First Embodiment)
FIG. 1 is a circuit diagram showing a configuration of a constant current circuit according to the first embodiment. The constant current circuit 10 of the present embodiment includes a constant current output unit 11 and a transconductance amplifier (gm amplifier) 12. The constant current output unit 11 has an NchMOS type transistor MN1 as an output transistor and a differential amplifier AMP1, the gate of the transistor MN1 is connected to the output end of the differential amplifier AMP1, and the source is the differential amplifier AMP1. It is connected to the inverting input end of. A resistor R1 as a first resistance element is connected between the source and ground of the transistor MN1, and a constant current circuit is formed by the transistor MN1, the differential amplifier AMP1, and the resistor R1. The constant current output unit 11 operates so that a current proportional to the voltage at the non-inverting input end of the differential amplifier AMP1 flows through the transistor MN1 to the resistor R1.

Further, the constant current output unit 11 includes an output reference voltage generation unit 13 shown below. The output reference voltage generation unit 13 has resistors R2, R3, and R4 as resistance elements connected in series, and a reference voltage source Vref1 as a first reference voltage generation unit is connected to the resistance R2, and the resistance R2 (first). The non-inverting input end of the differential amplifier AMP1 is connected to the connection node between the resistor R3 (third resistor element) and the resistor R3 (second resistor element). Further, it has an NPN type transistor QN1 as a first correction transistor, a collector of the transistor QN1 is connected to a reference voltage source Vref1, and an emitter is connected to a connection node between a resistor R3 and a resistor R4 (fourth resistance element). It is connected. The base of the transistor QN1 is connected to the drain of one PchMOS type transistor MP1 constituting the current mirror circuit, and a resistor R5 as a fifth resistance element is connected between the base of the transistor QN1 and the collector.

The constant current output unit 11 uses the voltage Va at the node A, which is the connection node between the resistor R2 and the resistor R3, as the output reference voltage, and generates the same voltage as the voltage Va across the resistor R1 by the differential amplifier AMP1 and the transistor MN1. And obtain a constant current output current IOUT. The output current IOUT is expressed by the following equation (10) in the same manner as the equation (5) described above.

IOUT = {Vref1-Vbe · (1-N)} / R1 ... (10)

The transconductance amplifier 12 includes NPN type transistors QN3, QN4, QN5, PNP type transistors QP1, QP2, QP3, and current sources I1, I2, I3, I4. Further, the transconductance amplifier 12 has a reference voltage source Vref2 as a second reference voltage generating unit and an NPN type transistor QN2 as a second correction transistor, and is referred to by the reference voltage source Vref2. The operation of the transistors QN3 to QN5 is turned on and off by comparing the voltage Vref2 with the base-emitter potential difference Vbe2 of the transistor QN2 or the emitter voltage Ve1 of the transistor QN1.

In the transconductance amplifier 12, power supply VDD is supplied to the current sources I2, I3, I4, the collector of the transistor QN3, and the source of the transistors MP1 and MP2 constituting the current mirror circuit. The emitter of the transistor QP2 and the base of the transistor QN4 are connected to the current source I2, the base of the transistor QP2 is connected to the emitter of the transistor QN1, and the collector of the transistor QP2 is grounded. The emitter of the transistor QP3 and the base of the transistor QN5 are connected to the current source I3, the base and collector of the transistor QP3 are connected to the base and collector of the transistor QN2, and the emitter of the transistor QN2 is grounded. That is, in the transistor QN2, the base and collector are short-circuited, the emitter is grounded, and the current source I3 is connected via the transistor QP3 so that a constant current flows through the collector. The emitter of the transistor QP1 and the base of the transistor QN3 are connected to the current source I4, the base of the transistor QP1 is connected to the reference voltage source Vref2, and the collector is grounded. The collectors of the transistors QN4 and QN5 are connected to the drain of the other transistor MP2 in the current mirror circuit. Then, the emitters of the transistors QN3, QN4, and QN5 are commonly connected, connected to the current source I1 as the first current source, and the other end of the current source I1 is connected to the ground.

In the transconductance amplifier 12, the input unit corresponds to the base of the transistors QP1, QP2, and QP3. The transistors QP1 to QP3 are elements as a level shift circuit of the input voltage, and the input voltage is shifted to a high voltage by the base-emitter potential difference Vbe of these elements. The transistors QP1, QP2, and QP3 may not be provided if the level shift circuit is not required. Therefore, substantially, the base of the transistor QN3 corresponds to the first input section of the transconductance amplifier 12, the base of the transistor QN4 corresponds to the second input section, and the base of the transistor QN5 corresponds to the third input section. Further, the transistors QN3, QN4, and QN5 are not limited to bipolar transistors, and may be MOSFETs or other switch elements.

Next, the operation in the constant current circuit 10 of this embodiment will be described.

The transconductance amplifier 12 compares the second reference voltage Vref2 with the voltage on the higher side of the base-emitter potential difference Vbe2 of the transistor QN2 and the emitter voltage Ve1 of the transistor QN1. If the higher voltage of Vbe2 and Ve1 is higher than the second reference voltage Vref2, the collector current of the transistor QN4 or QN5 flows. Here, when the base-emitter potential difference Vbe2 of the transistor QN2 is high, the transistor QN5 is turned on and the collector current flows, and when the emitter voltage Ve1 of the transistor QN1 is high, the transistor QN4 is turned on and the collector current flows. The collector current of the transistor QN4 or QN5 is folded back by the current mirror circuit by the transistors MP1 and MP2, and flows through the resistor R5 provided between the reference voltage source Vref1 and the transistor QN1. As a result, a correction voltage is generated in the resistor R5.

FIG. 2 is a characteristic diagram showing an example of temperature characteristics of each part in the constant current circuit of the embodiment. In FIG. 2, (A) shows the relationship between the voltage and temperature of the base-emitter potential difference Vbe2 of the transistor QN2 and the emitter voltage Ve1 of the transistor QN1, and (B) shows the relationship between the current and temperature of the drain current IdMP1 of the transistor MP1. It shows the relationship.

As shown in FIG. 2A, the base-emitter potential difference Vbe2 of the transistor QN2 has a negative temperature coefficient of about -2 mV / ° C. and the temperature when the current value of the current source I3 does not fluctuate significantly depending on the temperature. Decreases as the temperature rises. On the other hand, the emitter voltage Ve1 of the transistor QN1 has a positive temperature coefficient of about + 2 mV / ° C. and increases as the temperature rises because the base-emitter potential difference Vbe1 of the transistor QN1 decreases in the same manner as the transistor QN2. ..

Due to the above temperature characteristics, on the lower temperature side than the first predetermined temperature T1 in the operating temperature range, the base-emitter potential difference Vbe2 of the transistor QN2 is higher than the second reference voltage Vref2, the transistor QN5 is turned on, and the current source I1 A part of the current flows through the transistor QN5. When the transistor QN5 is turned on, a current flows through the resistor R5 and a correction voltage is generated. When the temperature rises and becomes higher than the first predetermined temperature T1, the base-emitter potential difference Vbe2 of the transistor QN2 decreases, both the transistor QN4 and the transistor QN5 are turned off, and all the current of the current source I1 flows to the transistor QN3. The temperature rises further, and on the higher temperature side than the second predetermined temperature T2, the voltage of the emitter voltage Ve1 of the transistor QN1 increases and becomes larger than the second reference voltage Vref2, the transistor QN4 is turned on, and the current of the current source I1. A part of the current flows through the transistor QN4. Here, the first predetermined temperature T1 ≦ the second predetermined temperature T2. When the transistor QN4 is turned on, a current flows through the resistor R5 and a correction voltage is generated.

As shown in FIG. 2B, the drain current IdMP1 flows through the transistor MP1 only when the transistor QN4 or the transistor QN5 is on the low temperature side or the high temperature side. As a result, on the lower temperature side than the first predetermined temperature T1 and the higher temperature side than the second predetermined temperature T2 in the operating temperature range, a current flows through the resistor R5 to generate a correction voltage, and the base voltage Vb1 of the transistor QN1 is set to the first. It is raised in comparison with the reference voltage Vref1 of.

FIG. 3 is a characteristic diagram showing an example of the temperature characteristics of the output current in the constant current circuit of the embodiment. As described above, the base voltage Vb1 of the transistor QN1 is raised by applying the correction voltage on the lower temperature side and the higher temperature side than the predetermined value in the operating temperature range, and the output current IOUT is increased by the raised voltage. As a result, the decrease in the output current IOUT on the low temperature side and the high temperature side can be corrected, and the decrease in the output current ΔIOUT (T) can be suppressed.

According to this embodiment, it is possible to correct the decrease in the output current IOUT due to the second-order temperature coefficient of the resistor R1 of the output unit in the constant current circuit. Therefore, the output current can be maintained with high accuracy in a wide temperature range, and the temperature characteristics can be further improved. Further, since a resistor element having a large second-order temperature coefficient can be used for the resistor R1 of the output unit, the choices of processes that can be used when mounting the constant current circuit on the IC are increased, and the degree of freedom in device design is increased. An improving effect can also be obtained.

(Second embodiment)
FIG. 4 is a circuit diagram showing the configuration of the constant current circuit of the second embodiment. The second embodiment shows another configuration example of the current source I1 in the first embodiment shown in FIG. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The configuration of the constant current output unit 11 is the same as that of the first embodiment.

The constant current circuit 10 of the first embodiment is configured to generate the tail current of the transconductance amplifier by the current source I1. The maximum value of the potential difference generated in the resistor R5 is the product of the current value of the current source I1 and the resistance value of the resistor R5. The resistor R5 has a temperature coefficient due to the resistance element, and the current value of the current source I1 also has a certain variation. The potential difference generated in the resistor R5 corrects the current value of the output current IOUT, and if this voltage fluctuates depending on the temperature characteristics of the resistor R5, it affects the accuracy of the output current IOUT.

The constant current circuit 10A of the second embodiment has a configuration for improving the voltage fluctuation due to the temperature characteristic of the resistor R5. The transconductance amplifier 12A of the constant current circuit 10A includes a constant current circuit including an NchMOS type transistor MN2, a differential amplifier AMP2, and a resistor R6, NchMOS type transistors MN3 and MN4, and PchMOS type transistors MP3 and MP4. It has a current mirror circuit configured to include. The current is generated in the constant current circuit by the transistor MN2, the differential amplifier AMP2, and the resistor R6, and the current is folded back in the current mirror circuit by the transistors MN3, MN4 and the transistors MP3, MP4. The resistor R6 corresponds to a sixth resistance element through which an output current flows in a constant current circuit. The constant current circuit and the current mirror circuit described above constitute a first current source that generates a tail current similar to that of the current source I1. A reference voltage source Vref1 is connected to the non-inverting input of the differential amplifier AMP2, and the first reference voltage Vref1 by the reference voltage source Vref1 is used as the reference voltage of the differential amplifier AMP2. The first current source is configured such that the output current value has a current value proportional to the value obtained by the product of the ratio of the resistance values of the resistors R5 and R6 and the first reference voltage Vref1.

In the constant current circuit 10A, the resistor R5 and the resistor R6 are composed of the same type of resistance element and the same temperature coefficient. By making the temperature characteristics of the resistor R5 and the resistor R6 equal to each other, the maximum value V _R5 of the potential difference generated in the resistor R5 is expressed by the following equation (11).

_VR5 = Vref1 ・ (R5 / R6)… (11)

In the equation (11), the potential difference generated in the resistance R5 is determined by the ratio of the resistance value of the resistance R5 and the resistance value of the resistance R6, and since the numerator denominator has the same temperature characteristics, it is affected by the temperature fluctuation of the resistance R5. No. Therefore, it is possible to obtain a correction voltage stable with respect to the temperature in the resistor R5. Further, since the reference voltage of the differential amplifier AMP2 is taken as the reference voltage source Vref1, the drain current of the transistor MN2 increases / decreases according to the increase / decrease of the first reference voltage Vref1, and the correction voltage is corrected. It is possible to suppress the change of.

According to the second embodiment, in addition to the effect of the first embodiment, the accuracy of the output current can be maintained without being affected by the fluttering due to the temperature of the resistance elements of the resistors R5 and R6. Therefore, the fluctuation of the maximum value of the potential difference generated in the resistor R5 can be suppressed, a constant current circuit having a small fluctuation in a wide temperature range can be realized, and the accuracy of the output current IOUT can be maintained with higher accuracy.

(Third embodiment)
FIG. 5 is a circuit diagram showing the configuration of the constant current circuit of the third embodiment. The third embodiment shows a configuration example in the case of using a resistance element having a negative temperature coefficient. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The configuration of the transconductance amplifier 12 is the same as that of the first embodiment.

The constant current circuits 10 and 10A of the first and second embodiments have a circuit configuration in which the first-order temperature coefficient of the resistor R1 is positive. The resistance element may have a negative temperature coefficient such as a polysilicon resistance. The constant current circuit 10B of the third embodiment is configured to perform temperature correction when a resistance element having a negative temperature coefficient is used for the resistance R1 or the like.

In the constant current circuit 10B, in the output reference voltage generation unit 13B of the constant current output unit 11B, the current source I5 as the second current source to which the power supply VDD is supplied and the PNP type transistor QP4 as the second correction transistor. And have. In the transistor QP4, the base is connected to the drain of one of the transistors MP1 in the current mirror circuit, the emitter is connected to the current source I5, and the collector is connected to the reference voltage source Vref1 and the collector of the transistor QN1. Further, resistors R2 and R3 connected in series between the emitter and collector of the transistor QP4 are connected, and the non-inverting input end of the differential amplifier AMP1 is connected to the connection node between the resistors R2 and R3, and the base-collector of the transistor QP4 is connected. A resistor R7 as a seventh resistance element is connected between them.

In the constant current output unit 11B, the potential difference between the emitter and the collector of the transistor QP4 decreases as the temperature rises, so that the voltage of the connection node between the resistor R2 and the resistor R3 has a negative temperature coefficient. By matching this temperature characteristic with the temperature coefficient of the resistance element of the resistor R1, it is possible to obtain an output current IOUT that is constant with respect to the temperature.

According to the third embodiment, when a resistor element having a negative temperature coefficient is used, it is possible to correct the decrease in the output current IOUT due to the second-order temperature coefficient of the resistor R1 in the constant current circuit. This makes it possible to maintain the output current with high accuracy in a wide temperature range, and further improve the temperature characteristics.

As described above, in the present embodiment, a correction resistance element that generates a correction voltage with respect to the temperature coefficient of the first resistance element that flows a constant current output current IOUT is provided, and a current is applied to the correction resistance element. It is equipped with a transconductance amplifier that supplies. The transconductance amplifier outputs a current according to the potential difference between the second reference voltage and the higher of the emitter voltage of the first correction transistor and the collector voltage of the second correction transistor. The output current is passed through the correction resistance element to generate a correction voltage in the correction resistance element. As a result, a correction voltage corresponding to the potential difference of the input portion of the transconductance amplifier is generated on the lower temperature side than the first predetermined temperature and on the higher temperature side than the second predetermined temperature, and the output current IOUT on the high temperature side and the low temperature side is generated by the correction voltage. Can be suppressed.

Therefore, it is possible to correct the temperature fluctuation of the output current not only with respect to the primary temperature coefficient of the resistance element to be used but also with respect to the secondary temperature coefficient, and the temperature characteristics can be further improved. Therefore, the output current accuracy in the entire operating temperature range of the constant current circuit can be improved, and a high-precision constant current circuit capable of keeping the output current constant in a wide temperature range can be realized.

Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, which naturally belong to the technical scope of the present invention. Understood. Further, each component in the above embodiment may be arbitrarily combined as long as the gist of the present invention is not deviated.

The present invention has the effect of further improving the temperature characteristics of the output current and improving the output current accuracy in the operating temperature range, and is useful for a constant current circuit that requires a constant current in a wide temperature range, for example. Is.

10, 10A, 10B: Constant current circuit 11, 11B: Constant current output unit 12, 12A: Transconductance amplifier 13, 13B: Output reference voltage generator Vref1, Vref2: Reference voltage source I1, I2, I3, I4, I5: Current source MN1, MN2: Transistor (NchMOS type)
MP1, MP2, MP3, MP4: Transistor (PchMOS type)
QN1, QN2, QN3, QN4, QN5: Transistor (NPN type)
QP1, QP2, QP3, QP4: Transistor (PNP type)
R1, R2, R3, R4, R5, R6, R7: Resistance

Claims (6)

A differential amplifier, a first resistance element having one end connected to the inverting input end of the differential amplifier and grounded at the other end, and a source or emitter connected to one end of the first resistance element so that the gate or base is the difference. The operation including an output transistor connected to the output end of the dynamic amplifier and a current proportional to the voltage at the non-inverting input end of the differential amplifier flows through the output transistor to the first resistance element. A constant current output unit that obtains a constant current from the drain or collector of the output transistor,
A first reference voltage generating section that generates a first reference voltage, a first correction transistor in which a collector is connected to the first reference voltage generating section, and a collector and an emitter of the first correction transistor. The second resistance element and the third resistance element connected in series between the two, and the correction resistance element inserted between the base and the collector of the first correction transistor are included. An output reference voltage generation unit that uses the connection node between the resistance element and the third resistance element as the output unit of the output reference voltage and supplies it to the non-inverting input end of the differential amplifier.
For the second correction, the second reference voltage generator that generates the second reference voltage, the base and the collector are short-circuited, the emitter is grounded, and the current source is connected so that a constant current flows through the collector. A first input unit includes a transistor and a voltage input corresponding to the second reference voltage, a second input unit receives a voltage input corresponding to the emitter voltage of the first correction transistor, and the second input unit. The input of the voltage corresponding to the collector voltage of the correction transistor is set as the third input section, and the higher of the voltage of the first input section, the voltage of the second input section, and the voltage of the third input section is used. A transconductance amplifier that outputs a current according to the potential difference between the voltage and
Equipped with
The output current of the transconductance amplifier flows through the correction resistance element, and the correction resistance element receives a potential difference between the voltage of the first input unit of the transconductance amplifier and the voltage of the second or third input unit. A constant current circuit that generates a correction voltage. The constant current circuit according to claim 1.
The output reference voltage generator is
It has an NPN transistor to be the first correction transistor, the emitter of the NPN transistor is connected to the second input portion of the transconductance amplifier, and one end to the emitter of the NPN transistor and the third resistance element. Has a fourth resistance element to which the other end is grounded and a fifth resistance element to be the correction resistance element, and the base of the NPN transistor is connected to the output unit of the transconductance amplifier. , Constant current circuit. The constant current circuit according to claim 1 or 2.
The transconductance amplifier is
It has third, fourth, and fifth transistors to which emitters are commonly connected, the base of the third transistor is the first input unit, the base of the fourth transistor is the second input unit, and the second. The base of the transistor of 5 is used as the third input unit.
The emitters of the third to fifth transistors are connected to the ground via the first current source, and the collectors of the fourth and fifth transistors are connected to each other to form a current mirror as an output unit of the transconductance amplifier. A constant current circuit that is connected to the input of the circuit and the output of the current mirror circuit is connected to the base of the first correction transistor. The constant current circuit according to claim 3.
The transconductance amplifier is
The fifth transistor is turned on on the lower temperature side than the first predetermined temperature, the fourth transistor is turned on on the higher temperature side than the second predetermined temperature higher than the first predetermined temperature, and the correction resistance element is turned on at each on. A constant current circuit that supplies current to the. The constant current circuit according to claim 3.
The first current source has a sixth resistance element having the same temperature coefficient as the correction resistance element as a resistance element for inputting the first reference voltage as a reference voltage and passing an output current, and has an output current value. Is a constant current circuit having a current value proportional to the value obtained by the product of the ratio of the resistance values of the correction resistance element and the sixth resistance element to the first reference voltage. The constant current circuit according to claim 1.
The output reference voltage generator is
It has a PNP type transistor to be the first correction transistor, an NPN type transistor in which a collector is connected to the collector of the PNP type transistor, and a second current source connected to the emitter of the PNP type transistor. A fourth resistance element in which the emitter of the NPN transistor is connected to the second input portion of the transconductance amplifier, one end is connected to the emitter of the NPN transistor and the other end is grounded, and the base of the NPN transistor. It has a fifth resistance element inserted between the collector and a seventh resistance element serving as the correction resistance element, and the base of the PNP type transistor is connected to the output unit of the transconductance amplifier. , Constant current circuit.

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