JPH0795674B2 - Transistor switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field B Outline of the Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems F Action G Example G-1 Configuration (Fig. 1) G-2 Operation (FIGS. 1 and 2) G-3 Modified Example H Effect of Invention A Field of Industrial Application The present invention relates to a transistor switching circuit having a hysteresis characteristic.

B. SUMMARY OF THE INVENTION The present invention is a switching circuit having a hysteresis characteristic, which is configured by using a transistor, and each emitter is connected to one end of a power source via a common current source unit to form a differential configuration. First and second current mirror units having different output current values are connected between the collector and the other end of the power source, respectively, and are connected to the first and second transistors, respectively, and A first resistance element, to which the output currents of the first and second current mirror sections are supplied, is connected between the base and one end of the power supply, and the first resistance element is thermally coupled to the resistance value. Includes a second resistance element that changes in response to a change in the resistance value of the first resistance element, and is connected to a current control unit that changes the current value of the current source section in accordance with the change in the resistance value of the second resistance element. It consists of the first Together with the base input voltage of Njisuta is applied, the collector current of the first transistor or the second
By deriving the voltage output or current output based on the base voltage or collector current of the transistor, the influence of power supply voltage fluctuations and temperature changes is reduced, and stable hysteresis characteristic operation is achieved. Based on this, a voltage output or a current output can be obtained.

C Prior Art As a switching circuit having a hysteresis characteristic configured by using the switching operation of a transistor,
For example, a Schmitt trigger circuit configured as shown in FIG. 3 is widely used.

The Schmitt trigger circuit shown in FIG.
The two transistors 11 and 12 are included, and the common resistor 13 is connected to the emitters of the two transistors 11 and 12. A load resistor 14 is connected to the collector of the transistor 11, and is also connected to the base of the transistor 12 via the resistor 15 and the capacitor 16, and the base of the transistor 12 is grounded via the resistor 17. A load resistor 18 is connected to the collector of the transistor 12 and an output terminal 19 is provided. In addition, transistor 11
An input terminal 20 is provided on the base of the. The resistance value of the load resistor 14 is set to be larger than the resistance value of the load resistor 18.

Then, for example, if the voltage Va applied to the input terminal 20 is the fourth
If it changes as shown in FIG. A, when the voltage Va is relatively low, the transistor 11 is turned off, and the power supply voltage Vcc is divided by the load resistor 14 and the resistors 15 and 17 at the base of the transistor 12. Voltage is applied and the state in which the transistor 12 is turned on is maintained. Thereby,
The emitter voltage Ve of the transistors 11 and 12 takes a high level Ve ₁ obtained by the collector current of the transistor 12 flowing through the common resistor 13 as shown in FIG. The output voltage Vo applied is at a low level, as shown in FIG. 4C.

Voltage Va gradually rises, the level Ve ₁ transistor 11
When it reaches a level V ₁ which is higher than the base-emitter on-voltage Vbe of the transistor, the transistor 11 is turned on and its collector voltage is lowered, whereby the transistor 12 is turned off. At this time, the emitter voltage Ve is
The collector current of 11 has a low level Ve ₂ obtained by flowing through the common resistor 13, and the output voltage Vo has a high level equal to the power supply voltage Vcc. After that, the voltage Va drops, and the on-state voltage Vbe between the base and the emitter becomes Vbe from the level Ve _2.
When the level becomes lower than the high level Ve ₂ , the transistor 11 is turned off, the transistor 11 is turned off and the transistor 12 is turned on again, and the output voltage Vo becomes low level.

In this manner, during the period from less than the voltage Va level V ₁ applied to the input terminal 20 the state after reaching the level V _1, to lower than low level V ₂ than the level V _1, the output terminal 19 A high level output voltage Vo is derived, and a hysteresis characteristic operation is obtained.

D Problems to be Solved by the Invention However, in the conventionally proposed switching circuit having the hysteresis characteristic as described above, the levels V ₁ and V ₂ which are switching voltage levels are influenced by the fluctuation of the power supply voltage Vcc and the temperature change. Will be changed easily,
Therefore, there is a drawback that the operation is not stable.

In view of such a point, the present invention is configured using a plurality of transistors, voltage output or current based on a stable hysteresis characteristic operation performed under the influence of fluctuations in power supply voltage, temperature changes, etc. It is an object to provide a transistor switching circuit adapted to obtain an output.

E Means for Solving the Problems In order to achieve the above-mentioned object, a transistor switching circuit according to the present invention comprises a first and a second transistor whose emitters are commonly connected to each other to form a differential structure, and 1
An input terminal for supplying an input voltage to the base of the transistor, an output terminal for deriving a current output or a voltage output based on the collector current of the first transistor or the base voltage or collector current of the second transistor, and
And a current source portion connected between the commonly connected emitter of the second transistor and one end of the power supply, and a first current source connected between the collector of the first transistor and the other end of the power supply.
Of the second current mirror section, which is connected between the collector of the second transistor and the other end of the power supply, and which has an output current value different from that of the first current mirror section, A first resistance element connected between the base of the transistor and one end of the power supply, and supplied with the output currents of the first and second current mirror sections; A second resistance element which is connected and whose resistance value changes in response to a resistance value change of the first resistance element;
A current control unit that changes the current value of the current source unit according to the change in the resistance value of the second resistance element is provided and configured.

In the transistor switching circuit according to the present invention configured as above, when the resistance value of the first resistance element changes, the second resistance element thermally connected to the first resistance element. The resistance value of changes in accordance with the change in the resistance value of the first resistance element, and the change in the resistance value of the second resistance element causes
When the resistance value of the first resistance element increases or decreases, the current value of the current source unit is correspondingly decreased or increased. Then, under such circumstances, an input voltage is supplied to the input terminal, and a current output or voltage output based on the collector current of the first transistor or the base voltage or collector current of the second transistor is derived at the output terminal. It As a result, the difference between the high level and the low level obtained by the voltage obtained at the base of the second transistor is stabilized against the fluctuation of the power supply voltage and the temperature change, and the influence of the fluctuation and the temperature change of the power supply voltage. The stability with a small value means that voltage output or current output based on the hysteresis characteristic operation can be obtained.

G Example G-1 Structure (FIG. 1) FIG. 1 shows an example of a transistor switching circuit according to the present invention.

In this example, the NPN transistors 21 and 22 are
These transistors 21 and 22 are provided so that their respective emitters are connected together to form a differential configuration.
Has their commonly connected emitters grounded through the collector-emitter path of an NPN transistor 23 forming a current source. Transistor 21 collector and power line
A PNP-type transistor 24 is diode-connected and inserted between the transistor 50 and 50, and the transistor 24 and the PNP-type transistor 25 connected thereto form a current mirror section 26. Where the ratio of the emitter area of the transistor 24 and the emitter area of the transistor 25 is n: m
(N and m are positive integers, and n <m). Therefore, the collector current of the transistor 25 is
It is n / m of the collector current of 24. Also, the transistor 22
A PNP-type transistor 27 is diode-connected and inserted between the collector and the power supply line 50, and the transistor 27 and the PNP-type transistor 28 connected to it form a current mirror section 29. ing. Here, the emitter area of the transistor 27 and the emitter area of the transistor 28 are selected to be equal to each other and, for example, equal to the emitter area of the transistor 24. Therefore, the collector currents of the transistors 27 and 28 are , Equal to each other and equal to the collector current of the transistor 24.

The collectors of the transistors 25 and 28 that form the current mirror units 26 and 29, respectively, are both connected to the base of the transistor 22, and the base of the transistor 22 is
Grounded via resistor 30. And the transistor
An input terminal 31 is provided on the base of 21 and an output terminal 32 is provided on the base of the transistor 22.

The base of the transistor 23 forming the current source is grounded via the collector-emitter path of the diode-connected NPN transistor 33,
The current flowing through the collector-emitter passage of 23 depends on the current flowing through the collector-emitter passage of the transistor 33. Between the commonly connected collector and base of the transistor 33 and the power supply line 50, the emitter-collector passage of the PNP transistor 34 is inserted.
The transistor 34 and the diode-connected PNP transistor 35 form a current mirror section 36. In the current mirror section 36, the emitter area of the transistor 34 and the emitter area of the transistor 35 are selected to be equal to each other, and therefore the collector currents of the transistors 34 and 35 are equal to each other.

A collector-emitter path of an NPN transistor 37 and a resistor 38 are inserted in series between the commonly connected collector and base of the transistor 35 and the ground potential point. The base of the transistor 37 is connected to the output terminal of the comparator 40 that compares the voltage obtained across the resistor 38 with the reference voltage supplied from the stabilized voltage source 39. The transistor 37, the regulated voltage source 39 and the comparator 40 are
The collector current of the transistor 35 forming the current mirror unit 36 is controlled so that the voltage obtained across the resistor 38 is a constant voltage having a constant relationship with the reference voltage supplied from the stabilized voltage source 39. ing.

Then, at least the resistor 30 and the resistor 38 are thermally connected to each other, and are placed under the same temperature change state. Such thermal connection is easily achieved, for example, by forming the resistance 30 and the resistance 38 together with the above-mentioned transistors into an integrated circuit element and forming them on the same semiconductor chip.

G-2 Operation (FIGS. 1 and 2) First, as described above, the resistance 30 and the resistance 38 are used under the power supply voltage from the common power supply line 50, and the same temperature change state is used. As a result, the current Io flowing through the collector-emitter path of the transistor 23 forming the current source fluctuates according to the fluctuation of the resistance value R of the resistor 30, and the fluctuation mode increases or decreases. It is supposed to decrease or increase in response to the decrease. That is, for example, when the resistance value R increases due to the fluctuation of the power supply voltage or the temperature change, the resistance value of the resistor 38 also increases at the same time. The voltage available across resistor 38 is applied to current mirror section 36 by transistor 37, regulated voltage source 39 and comparator 40.
Since the collector current of the transistor 35 forming the transistor is controlled and maintained constant, the collector current Ia of the transistor 35 is reduced as the resistance value of the resistor 38 increases. Therefore, the collector current Ia of the transistor 34 that forms the current mirror section 36 together with the transistor 35 can also be reduced. This transistor 34
The collector current Ia of the transistor 23 flows through the collector-emitter path of the transistor 33 connected to the base of the transistor 23.
The current Io flowing through the emitter passage is reduced.

When the resistance value R decreases, the current Io flowing through the collector-emitter passage of the transistor 23 increases under the same operation as described above. Under such circumstances, for example,
When the resistance value R fluctuates, the current Io changes accordingly, and the product R · Io of the resistance value R and the current Io is set to be kept constant.

Then, for example, if the voltage Vi applied to the input terminal 31 is the second
If it changes as shown in FIG. A, when the voltage Vi is relatively low, the transistor 21 is turned off and the transistor 22 is turned on. As a result, the current Io set by the transistor 23 forming the current source flows through the collector of the transistor 27 forming the current mirror unit 29 and the transistor 22.
A current mirror unit 29 is configured with the transistor 27,
The current Io is supplied to the resistor 30 from the transistor 28 which causes a collector current equal to the collector current of the transistor 27 to flow. Therefore, the voltage Vb obtained at the base of the transistor 22 is
As shown in FIG. 2B, takes a high level Vh determined by the product R · Io of the resistance value R of the resistor 30 and the current Io, and the voltage Vb having this high level Vh is applied to the output terminal 32. Derived.

When the voltage Vi rises and reaches a level Vh ′ that is slightly higher than the level Vh of the voltage Vb at the base of the transistor 22, the transistor 21 is turned on and the transistor 22 is turned off. As a result, the collector of the transistor 24 and the transistor 21 forming the current mirror section 26 are
A current Io set by a transistor 23 forming a current source flows through the transistor 24, and accordingly, a current mirror unit 26 is formed together with the transistor 24, and a collector current that is n / m of the collector current of the transistor 24 flows. From 25, a current Io · n / m is supplied to the resistor 30. Therefore, at this time, the voltage obtained at the base of the transistor 22
As shown in FIG. 2B, Vb takes a low level Vl determined by the product R · Io · n / m of the resistance value R of the resistor 30 and the current Io · n / m, and takes this low level Vl. The voltage Vb is led to the output terminal 32.

After that, the voltage Vi drops and the transistor 22 at that time
A level slightly higher than the level Vl of the voltage Vb at the base of
When it becomes lower than Vl ', the transistor 11 is turned off and the transistor 22 is turned on again. As a result, the voltage Vb obtained at the base of the transistor 22 again has a high level Vh determined by the product R · Io of the resistance value R of the resistor 30 and the current Io, and the voltage Vb having the high level Vh is the output terminal. Derived to 32.

In this way, after the voltage Vi applied to the input terminal 31 reaches the level Vh ′ from the state of being lower than the level Vh ′,
The voltage Vb having the low level Vl is derived at the output terminal 32 until the voltage becomes lower than the level Vl 'below Vh', and the hysteresis characteristic operation is obtained.

In such a hysteresis characteristic operation, the transistor 22
High level Vh and low level taken by the voltage Vb obtained at the base of
The difference from Vl, and hence the level difference of the voltage obtained at the output terminal 32, that is, the output voltage level difference ΔV, is ΔV = Vh−Vl = R · Io−R · Io · n / m = R · Io · ( 1-n / m) When n / m = k (<1), ΔV = R · Io · (1-k). As described above, the current Io flowing through the collector-emitter path of the transistor 23 fluctuates according to the fluctuation of the resistance value R of the resistor 30, and the fluctuation mode thereof decreases or increases corresponding to the increase or decrease of the resistance value R. Since the product of the resistance value R and the current Io is kept constant, the output voltage level difference ΔV = (1−k) · R · Io is set to a constant value.

As a result, the resistance 30
Even when the resistance value R of the above changes, a stable voltage output whose influence is extremely small is led to the output terminal 32.

Here, switching when the voltage Vi applied to the input terminal 31 rises will be considered.

In the transitional period of switching, in which the transistor 21 is turned off and the transistor 22 is turned on, the transistor 21 is turned on and the transistor 22 is turned off.
Current flows in the collector-emitter path of each of the transistors, but the level difference between the voltage V i applied to the input terminal 31 and thus to the base of the transistor 21 and the voltage Vb at the base of the transistor 22 is Vd, and the collector of the transistor 21- Assuming that the current flowing through the emitter passage is I ₁ and the current flowing through the collector-emitter passage of the transistor 22 is I ₂ , I ₁ + I ₂ = Io It is expressed as I ₂ = Io−I ₁ = exp (−Vd / V _T ), where V _T is the thermal potential.
Further, in such a state, the current from both the transistor 25 and the transistor 27 is supplied to the resistor 30, The loop gain Gl of the circuit including the transistors 21 and 22 is The transistor 21 is off and the transistor 22 is on.
Is inverted, that is, Vd becomes the inverted voltage Vdi when the loop gain Gl becomes 1. Vd that satisfies is Vdi. Therefore, using the relation of equation (1), The relationship is obtained.

Here, if exp (Vdi / V _T ) >> 1 then exp (Vdi / V _T ) = R · Io · (1-k) / V _T = ΔV / V _T. ΔV is constant and may be considered as a constant, and the relationship Vdi = V _T · ln (ΔV / V _T ) is obtained.

Since V _T = kT / q, (k is Boltzmann's constant, T is absolute temperature, q is electron charge), the change due to temperature fluctuation of Vdi is Becomes

Assuming that the change represented by the equation (2) is zero, ln (ΔV / V _T ) = (1 / log e) ≈2.3 (3)

Therefore, by setting the output voltage level difference ΔV that satisfies the expression (3), the change in the inversion voltage Vdi due to the temperature fluctuation can be made extremely small. Indeed In may be selected to [Delta] V to approximately 10 times the V _T, as V _T ≒ 26 mV, it may be set to [Delta] V ≒ 260 mV. Output voltage level difference ΔV
The value of 260 mV in is a value that is easy to handle in actual use.

In this way, the change due to the temperature change of the inversion voltage Vdi is made extremely small, so that the transistor 21 and
The switching voltage level at 22 becomes stable because the influence of temperature change is small, and the hysteresis characteristic operation is performed stably.

G-3 Modification Example In the above example, the output terminal 32 is a transistor.
It is provided at the base of the transistor 22 so as to obtain a voltage output based on the voltage obtained at the base of the transistor 22. Instead of such an output terminal 32, for example, the base is the collector of the transistor 21 or 22. To add a PNP-type transistor which is connected and whose emitter is connected to the power supply line 50, and to provide an output terminal at the collector of such a transistor so as to obtain a current output based on the collector current of the transistor 21 or 22. You can also

H Effect of the Invention As is clear from the above description, according to the transistor switching circuit of the present invention, an input voltage is applied to one base of one of the transistors forming a pair of differential configurations that perform a switching operation. , A voltage output or current output based on the collector current of one of these or the voltage obtained at the base of the other or the current flowing through the collector is derived, and the voltage obtained at the other base of the transistors forming the differential configuration is then derived. The difference between the high level and the low level is stabilized against changes in the power supply voltage or temperature changes, which stabilizes the voltage output or current output against changes in the power supply voltage or temperature changes. As a result, the voltage output or current output has a stable hysteresis that is less affected by fluctuations in power supply voltage, temperature changes, etc. It is those obtained on the basis of the characteristic operation.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a transistor switching circuit according to the present invention, FIG. 2 is a voltage level diagram for explaining the operation of the example shown in FIG. 1, and FIG. 3 is a conventional Schmitt trigger circuit. FIG. 4 is a voltage level diagram for explaining the operation of the circuit shown in FIG. In the figure, 21, 22, 23, 33 and 37 are NPN type transistors, 26, 2
9 and 36 are current mirror sections, 30 and 38 are resistors, 31 is an input terminal, 32 is an output terminal, 39 is a regulated voltage source, and 40 is a comparator.

Claims (1)

[Claims] 1. A first and a second transistor having respective emitters connected in common to form a differential structure, an input terminal for supplying an input voltage to a base of the first transistor, and the first transistor. Collector current of the second or above
An output terminal for deriving a current output or a voltage output based on the base voltage or collector current of the transistor, and a current source section connected between the commonly connected emitters of the first and second transistors and one end of the power supply. A first current mirror section connected between the collector of the first transistor and the other end of the power supply; and a first current mirror section connected between the collector of the second transistor and the other end of the power supply, The first current mirror section is connected between a second current mirror section having an output current value different from that of the first current mirror section, a base of the second transistor and one end of the power supply, and the first and second current mirror sections are connected. A first resistance element to which the output current of the mirror portion is supplied, and a first resistance element that is thermally connected to the first resistance element and has a resistance value of the first resistance element.
A current control unit that includes a second resistance element that changes in response to a change in the resistance value of the resistance element, and that changes the current value of the current source section in accordance with the change in the resistance value of the second resistance element. A transistor switching circuit that is equipped with.