JP2003015754A - Reference voltage generating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reference voltage generating circuit which can generate a reference voltage having a desired temperature coefficient and in which the circuit configuration is simplified and current consumption is reduced. SOLUTION: A constant current circuit 14, diodes D11-D15, and the drain and source of an MOS transistor Q11 whose gate and drain are connected are serially connected between power lines 12 and 13. The temperature coefficient of an inter-drain/source voltage VDS is changed according to drain currents ID. The current value of the constant current circuit 14 is set so that the inner-drain/source voltage VDS can be provided with a positive temperature coefficient and so that the voltage between both ends of a series circuit 15 can be provided with the temperature coefficient equivalent to a forward voltage (2.VF). Thus, the temperature coefficient of a reference voltage Vref can be turned to be almost 0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage generating circuit that outputs a DC voltage.

[0002]

For example, an on-vehicle electronic control device and a portable electronic device are used under various temperature environments, and therefore must be constructed so as to be operable in a wide temperature range. Therefore, the IC used in these devices requires a circuit that generates a reference voltage having a small temperature coefficient. The bandgap reference voltage circuit 1 shown in FIG. 9 is frequently used. Since the bandgap reference voltage circuit 1 needs to be configured by using the operational amplifier 2, the circuit scale becomes large, and the resistors R1 to R3 need to be trimmed in order to obtain sufficiently high accuracy.

On the other hand, a zener diode having a zener voltage near 5 V has a temperature coefficient of almost 0 depending on its use condition. Therefore, as shown in FIG.
The Zener diode 4 can be used as long as it is applied to the 5V reference voltage generating circuit 3. However, in order to use the Zener diode 4 in a stable voltage state, it is necessary to pass a relatively large current (for example, 1 mA), and thus it is difficult to adopt it in a device that operates using a battery (battery) as a power source.

In the above example, a reference voltage having a small temperature coefficient is generated, but there are cases where a reference voltage having a predetermined positive or negative temperature coefficient instead of 0 is required. For example, an alternator that charges a vehicle-mounted battery is controlled to output electric power according to the temperature of the battery in order to extend the life of the battery. The control device that performs this power control is provided integrally with the alternator. The control device is provided with an IC-based reference voltage generating circuit, and the temperature (approximately equal to the temperature of a battery installed in the same engine room) is based on the change in the reference voltage.
Is detected and the exciting current of the alternator is adjusted. Conventionally, the forward voltage of the diode is used as this reference voltage, but a reference voltage generating circuit capable of generating a reference voltage having a predetermined temperature coefficient is desired in order to increase the degree of freedom in circuit design.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a reference voltage generating circuit which can generate a reference voltage having a desired temperature coefficient, has a simple circuit configuration, and consumes less current. Especially.

[0006]

According to the means described in claim 1, the output reference voltage is the drain-source voltage of the FET.
It becomes a voltage obtained by adding the voltage between the sources and the forward voltage of the diode. Each of the FET and the diode is composed of one element or a plurality of elements connected in cascade. Here, the forward voltage of the diode has a substantially constant negative temperature coefficient according to the number of series elements. On the other hand, the temperature coefficient of the drain-source voltage of the FET has any value within the range from positive to negative depending on the current as described below.

That is, in the FET in which the gate and the drain are connected, when the drain-source voltage (that is, the gate-source voltage) reaches the threshold voltage Vt, the drain current starts to flow. The drain-source voltage is determined by the threshold voltage Vt being dominant in the region where the drain current is small, and is determined by the voltage drop due to the ON resistance being dominant in the region where the drain current is large. A general FET has a characteristic that the threshold voltage Vt decreases and the on-resistance increases as the temperature rises. That is, when the drain current is low, the drain-source voltage becomes lower as the temperature rises, and when the drain current is high, the drain-source voltage becomes higher as the temperature rises. Has a temperature coefficient of. The temperature coefficient becomes 0 at these intermediate drain currents.

Therefore, by setting the value of the current flowing in the series circuit of the FET and the diode to an appropriate value, a reference voltage having a desired temperature coefficient within a positive to negative range is taken out from between both terminals of the series circuit. be able to. For example, a reference voltage with a temperature coefficient of 0 can be used as a reference voltage in an analog circuit, and a reference voltage with a temperature coefficient of a predetermined positive or negative value can be used as temperature detecting means. Further, since the current value (40 μA as an example) passed through the series circuit is sufficiently smaller than the current value (1 mA as an example) required for stable operation of the Zener diode, the current consumption can be reduced. .

According to the means described in claim 2, the FET
Since the drain-source voltage of has a positive temperature coefficient and the positive temperature coefficient is equal to the absolute value of the negative temperature coefficient of the diode forward voltage, it is output from both terminals of the series circuit. The temperature coefficient of the reference voltage becomes almost zero.

According to the third aspect, the reference voltage to be output is determined by the lower one of the drain-source voltage of the FET and the forward voltage of the diode being dominant. 1 for each FET and diode
Element or a plurality of elements connected in a cascade. As described above, the temperature coefficient of the drain-source voltage of the FET has any value within the range from positive to negative depending on the current, and the temperature coefficient of the forward voltage of the diode depends on the number of series elements. Has a substantially constant negative value.

Therefore, by setting the current value flowing in the parallel circuit of the FET and the diode to an appropriate value, and setting the drain-source voltage of the FET and the forward voltage of the diode to an appropriate value. , A reference voltage having a desired temperature coefficient can be output from both terminals of the parallel circuit. Further, depending on the setting, it is possible to output a reference voltage having a mountain-shaped or valley-shaped temperature characteristic.

According to the means described in claim 4, at a temperature lower than the predetermined temperature, the reference voltage exhibits a positive temperature coefficient because the drain-source voltage of the FET becomes predominant. At a temperature higher than the temperature, the forward voltage of the diode becomes dominant and shows a negative temperature coefficient.
That is, it has a mountain-shaped or valley-shaped temperature characteristic. As a result, the change width of the reference voltage in the entire temperature change range is smaller than that of the reference voltage generating circuit using only the FET or the diode.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows the electrical configuration of the reference voltage generating circuit. The reference voltage generation circuit 11 shown in FIG.
For example, it is configured as an IC used in an electronic control unit (ECU) mounted on a vehicle.

Between the positive power supply line 12 and the negative power supply line 13, a constant current circuit 14 for outputting 40 μA, diodes D11 to D15 of the illustrated polarity, and an N channel connected between the gate and drain are provided. Type MOS transistor Q11
The drain and source of are connected in series. Here, the diodes D11 to D15 and the MOS transistor Q
A series circuit 15 is constituted by 11 and 11. The size of the MOS transistor Q11 is L / W = 40 μm / 23 μ
It is supposed to be m.

Power line 12 and output terminal 1 for reference voltage Vref
6 and NPN type transistors Q12 and Q13
Are connected by Darlington, and the output circuit is configured by. The base of the transistor Q12 is the series circuit 15
Is connected to the positive side terminal of the transistor Q12, that is, the anode of the diode D11, and the resistor R11 is connected between the emitter of the transistor Q12 and the output terminal 16, that is, between the base and emitter of the transistor Q13.

In this configuration, a part of the output current of the constant current circuit 14 becomes the base current of the transistor Q12,
The transistors Q12 and Q13 can supply a sufficient current to a load (not shown) connected to the output terminal 16. Further, most of the output current of the constant current circuit 14 flows to the series circuit 15, and the voltage across the series circuit 15 is the drain-source voltage VDS of the MOS transistor Q11 and the forward voltage (5.VF) of the diodes D11 to D15. ) And the added voltage. At this time, the reference voltage Vref output from the output terminal 16 is the voltage across the series circuit 15 (VDS + 5.
The voltage becomes a voltage lower than the base-emitter voltage (2.VF) of the transistors Q12 and Q13 with respect to (VF).

FIG. 2A shows M with temperature as a parameter.
3 schematically shows the static characteristics of the OS transistor Q11. In FIG. 2A, the horizontal axis represents the drain-source voltage VDS, and the vertical axis represents the drain current ID. The three characteristic lines indicated by "HT", "RT", and "LT" indicate the characteristics at high temperature, room temperature, and low temperature, respectively. FIG. 2B schematically shows the temperature characteristic of the drain-source voltage VDS of the MOS transistor Q11 with the drain current ID as a parameter. In FIG. 2B, the horizontal axis represents the temperature and the vertical axis represents the drain-source voltage VDS.

As shown in FIG. 2A, the MOS transistor Q11 has a threshold voltage V
It has a characteristic that t decreases and on-resistance increases.
Further, the drain-source voltage VDS is the drain current I
The threshold voltage Vt is dominant in the region where D is small, and the voltage drop due to the on-resistance is dominant in the region where the drain current ID is large.

Therefore, as shown in FIG. 2B, the drain-source voltage VDS has a negative temperature coefficient and the drain current ID is large when the drain current ID is small (ID = ID3). In the case of (ID = ID1), it has a positive temperature coefficient. The temperature coefficient becomes 0 at these intermediate drain currents (ID = ID2). On the other hand, the forward voltage VF of the diodes D11 to D15 and the base-emitter voltage VBE of the transistors Q12 and Q13 each have a negative temperature coefficient (about -2 mV / ° C).
have.

Therefore, in order to set the temperature coefficient of the reference voltage Vref to 0, the drain current ID of the MOS transistor Q11 is set larger than the current ID2, and the drain-source voltage VDS has a positive temperature coefficient. In addition, the forward voltage (2 · VF) is applied to the voltage across the series circuit 15.
It suffices to have a temperature coefficient corresponding to. This series circuit 1
The temperature coefficient of the voltage between both ends of transistor 5 is
It is canceled by the temperature coefficient of the base-emitter voltage (2 · VF) of 3.

FIG. 3 shows the reference voltage generating circuit 11 shown in FIG.
The simulation results of the reference voltage Vref and the drain-source voltage VDS of the MOS transistor Q11 are shown. The drain-source voltage VDS has a positive temperature coefficient (5 mV / ° C.), and the reference voltage Vref is almost constant at 5.2V to 5.3V regardless of temperature change.

As described above, according to this embodiment, the MOS transistor Q11 and the diodes D11 to D11.
15 is connected in series and the output current of the constant current circuit 14 is 40μ.
By setting to A, the MOS transistor Q11 has a positive temperature characteristic opposite to that of the diodes D11 to D15, so that the temperature characteristic of the reference voltage Vref can be almost zero. In this case, the current value (40 μA) is sufficiently smaller than the current value (eg, 1 mA) required for stable operation of the Zener diode, so that the IC
It is possible to reduce current consumption during the operation and standby current during standby. In addition, since the circuit configuration is simple without using an operational amplifier or the like, the circuit size in the IC chip can be reduced and the cost can be reduced.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
2 shows an electrical configuration of the reference voltage generation circuit 17 according to the embodiment. The reference voltage generating circuit 17 differs from the reference voltage generating circuit 11 shown in FIG. 1 in that a P-channel type MOS transistor Q14 is used, but both circuits are substantially the same circuit.

That is, between the power lines 12 and 13,
MOS transistor Q whose gate and drain are connected
Between the source and drain of 14, diode D1 of the polarity shown
1 to D15 and the constant current circuit 14 are connected in series. Here, the MOS transistor Q14 and the diodes D11 to D15 form a series circuit 18. Between the output terminal 16 and the power supply line 13, PNP type transistors Q15 and Q16 are Darlington connected. The reference voltage Vref is output from the output terminal 16 using the potential of the power supply line 12 as a reference potential.
According to this embodiment, the same operation and effect as those of the first embodiment can be obtained.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 5 shows an electrical configuration of the reference voltage generation circuit 19. In FIG. 5, the power supply line 12 and the output terminal 16
A constant current circuit 14 is connected between and. Further, between the output terminal 16 and the power supply line 13, the drain and the drain of the MOS transistor Q11 connected between the gate and the drain are connected.
A parallel circuit 20 including diodes D11 to D15 connected in series with the sources is connected. In this configuration,
The current value of the constant current circuit 14 and the number of diodes connected in series (5 in this embodiment) are determined so as to satisfy the following two conditions.

All the currents of the first condition constant current circuit 14 are MOS transistors Q11.
Drain-source voltage VDS
Has a positive temperature coefficient, and the positive temperature coefficient is equal to the absolute value of the negative temperature coefficient of the forward voltage (5 · VF) of the diodes D11 to D15 connected in series.

Second condition At a predetermined temperature Ta, the drain-source voltage VDS of the MOS transistor Q11 is equal to the forward voltage (5.VF) of the diodes D11 to D15 connected in series.

Reference voltage Vre output from the output terminal 16
f is determined by the lower one of the drain-source voltage VDS of the MOS transistor Q11 and the diode forward voltage (5.VF). FIG. 6 shows the above 2
It is a diagram schematically showing the temperature characteristics of the reference voltage Vref when the conditions are satisfied. When the temperature is lower than Ta (temperature region A shown in FIG. 6), the drain-source voltage VDS of the MOS transistor Q11 becomes lower than the forward voltage (5 · VF) of the diodes D11 to D15, and the reference voltage Vref exhibits a positive temperature characteristic according to the drain-source voltage VDS of the MOS transistor Q11.

On the other hand, when the temperature is higher than Ta (temperature region B shown in FIG. 6), the forward voltage (5.VF) of the diodes D11 to D15 is higher than the drain-source voltage VDS of the MOS transistor Q11. It becomes low and the reference voltage V
ref is the forward voltage (5 · V) of the diodes D11 to D15.
F) shows negative temperature characteristics. As a result, the reference voltage Vref has a mountain-shaped temperature characteristic that takes the maximum value at the temperature Ta.

By providing such a mountain-shaped temperature characteristic, as compared with the reference voltage generation circuit using only the MOS transistor Q11 or the diodes D11 to D15, the reference voltage Vref in the entire temperature change range is seen.
It is possible to reduce the range of change in temperature and increase stability with respect to temperature.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. 7 and 8. The reference voltage generation circuit 21 shown in FIG. 7 is different from the reference voltage generation circuit 19 shown in FIG. 5 in using a P-channel type MOS transistor Q14, but both circuits are substantially the same circuit. .

That is, between the power supply line 12 and the output terminal 16, a parallel circuit 22 is connected between the source and drain of the MOS transistor Q14 whose gate and drain are connected and the diodes D11 to D15 which are connected in series. Has been done. A constant current circuit 14 is connected between the output terminal 16 and the power supply line 13. Current value of constant current circuit 14 and number of diodes connected in series (5 in this embodiment)
Are determined so as to satisfy the same conditions as the two conditions described in the third embodiment. The reference voltage Vref is
The potential of the power supply line 12 is used as a reference potential to be output from the output terminal 16.

According to this embodiment, the reference voltage Vref has a valley-shaped temperature characteristic that becomes the minimum value at the temperature Ta by the same operation as that of the third embodiment. As a result, the change width of the reference voltage Vref in the entire temperature change range can be made smaller than that of the reference voltage generating circuit using only the MOS transistor Q11 or the diodes D11 to D15.

(Other Embodiments) The present invention is not limited to the embodiments described above and shown in the drawings, and can be modified or expanded as follows, for example.
In the first and second embodiments, the temperature coefficient of the reference voltage Vref is set to 0, but the desired positive or negative temperature coefficient can be obtained by changing the current value of the constant current circuit 14 and the number of connected diodes. You can In addition, transistors Q12, Q13 (Q15, Q1) connected in Darlington
The output circuit consisting of 6) may be added if necessary. In each embodiment, the MOS transistor and the diode can each be composed of one element or a plurality of elements connected in cascade. Also, MO
Not limited to the S transistor, a junction FET or the like may be used.

[Brief description of drawings]

FIG. 1 is an electrical configuration diagram of a reference voltage generation circuit showing a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing static characteristics (a) of a MOS transistor and temperature characteristics (b) of a drain-source voltage VDS.

FIG. 3 is a simulation diagram showing a reference voltage Vref and a temperature characteristic of a drain-source voltage VDS of a MOS transistor.

FIG. 4 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 5 is a view corresponding to FIG. 1 showing a third embodiment of the present invention.

FIG. 6 is a diagram schematically showing temperature characteristics of a reference voltage Vref under two predetermined conditions.

FIG. 7 is a diagram corresponding to FIG. 1 showing a fourth embodiment of the present invention.

FIG. 8 is a view corresponding to FIG.

FIG. 9 is an electrical configuration diagram showing a bandgap reference voltage circuit which is a conventional technique.

FIG. 10 is an electrical configuration diagram showing a reference voltage generation circuit using a Zener diode.

[Explanation of symbols]

Reference numerals 11, 17, 19, and 21 are reference voltage generation circuits, 14 is a constant current circuit, 15 and 18 are series circuits, 22 is a parallel circuit, and Q is a circuit.
11, Q14 are MOS transistors (FET), D11
~ D15 is a diode.

Claims (4)

[Claims] 1. A FET having a gate and a drain connected to each other.
A reference voltage characterized by comprising a series circuit of a diode and a diode, and a constant current circuit for supplying a predetermined current to the series circuit, wherein the reference voltage is output between both terminals of the series circuit. Generator circuit. 2. The current value of the constant current circuit is the FET
The voltage between the drain and source of the diode has a positive temperature coefficient, and the positive temperature coefficient and the absolute value of the negative temperature coefficient of the forward voltage of the diode are set to be equal to each other. The reference voltage generating circuit according to claim 1, which is characterized in that. 3. A FET having a gate and a drain connected to each other.
And a diode in parallel, and a constant current circuit that causes a predetermined current to flow in the parallel circuit, and the reference voltage is configured to output a reference voltage between both terminals of the parallel circuit. Generator circuit. 4. The current value of the constant current circuit has a positive temperature coefficient in the drain-source voltage when the current flows through the FET, and the positive temperature coefficient and the order of the diode are constant. It is set to a value such that the absolute value of the negative temperature coefficient of the directional voltage is equal to each other. In the parallel circuit, the drain-source voltage of the FET and the forward voltage of the diode are set at a predetermined temperature. The reference voltage generation circuit according to claim 3, wherein the reference voltage generation circuits are configured to be equal to each other.