JP2830516B2 - Current comparator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current comparator having a hysteresis characteristic.

[0002]

2. Description of the Related Art Conventionally, this type of current comparator has a circuit configuration as shown in FIG. That is, in FIG. 4, the input currents I1 and I2 are input to a current-voltage conversion circuit 41a and a current-voltage conversion circuit 41b, respectively, are converted into voltages V1 and V2, respectively, and are input to a differential amplifier 42. Output Vod of dynamic amplifier 42
Is input to the inverting input terminal 44 of the comparator 43 and compared with the reference voltage VR to obtain an output VO.

A resistor 47 is connected between the non-inverting input terminal 45 of the comparator 43 and the output terminal 46, and a resistor 48 is connected between the non-inverting input terminal 45 of the comparator 43 and the reference voltage VR. As a voltage comparator having a hysteresis characteristic.

Further, current-voltage conversion circuits 41a, 41b
A generally known circuit configuration as shown in FIG. 5 is used. That is, in FIG. 5, an input current I is converted into a voltage by a resistor 52 connected between an inverting input terminal 53 and an output terminal 55 of the operational amplifier 51, and
Has a configuration in which a DC voltage VDC is applied to the non-inverting input terminal 54 and an output voltage V = VDC-I × R is obtained.

[0005]

However, in the conventional current comparator, two input currents are first converted into voltages by current-voltage conversion circuits 41a and 41b in order to compare the two input currents, and then differentially amplified by a differential amplifier 42. After amplification, the voltage must be compared with the reference voltage VR by using the comparator 43. Since the circuit is complicated and the number of components is large, the power consumption is large, and there is a problem that the circuit is not suitable for IC. In addition, since current-voltage conversion is performed using the resistor 52, when the input current is small, a high resistance is required,
Further, when the input current is large, a low resistance is required, and when the range of the input current is wide, the resistance has to be switched. Furthermore, in order to be stable against temperature and current fluctuations, a reference voltage source free from temperature fluctuations and power supply fluctuations is required. However, a reference voltage source that satisfies both of them is expensive and cannot be easily obtained. There was a problem.

Accordingly, the present invention has been made in view of such conventional problems, and has as its object the purpose of reducing power consumption, easily implementing an IC, widening the input current range, and preventing temperature fluctuation and power supply fluctuation. And providing a stable current comparator.

[0007]

In order to achieve the above object, a current comparator according to the present invention comprises a first transistor having a collector and a base connected to each other and an emitter grounded, and a first transistor having a base connected to the first transistor. A second transistor connected to the base of the transistor and having the emitter grounded, and a third transistor connected to the collector and the base and having the emitter grounded
, A fourth transistor having a base connected to the base of the third transistor, an emitter grounded, and a first input terminal connected to the collector of the first transistor and the collector of the fourth transistor. And the second
A second input terminal to which the collector of the third transistor is connected to the collector of the third transistor, a first input terminal,
A second input end and an output end, wherein the first input end is the first input end;
And an output circuit having a second input terminal connected to the second input terminal and an output terminal connected to the output terminal, wherein the area of the emitter region of the second transistor and the first circuit are connected. The ratio of the area of the transistor to the area of the emitter region;
The ratio between the area of the emitter region of the third transistor and the emitter region of the third transistor has a value larger than 1.

[0008]

In the present invention, the current comparator is composed of two sets of current mirror circuits each composed of a diode-connected transistor and a transistor having a common base, and an output circuit. Since there are not many components and the IC is easy to implement, the power consumption is large and the IC
The problem of being unsuitable for conversion is solved. In addition, since the matching between elements in the IC is extremely good, the threshold value and hysteresis width of the input / output characteristics are determined only by the area ratio of the emitter region of the transistor. Is obtained on the basis of grounding, so that it is not affected by fluctuations in the power supply, and the problem that it is not easy to obtain a stable element against fluctuations in temperature and power supply is solved. It is known that a current mirror circuit generally operates stably in a wide current range of 6 digits or more. When the input current range is widened, the inconvenience of having to switch the resistance is eliminated.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a circuit configuration according to an embodiment of the current comparator according to the present invention. In the figure, an NPN transistor 11 having a collector and a base connected to each other and an emitter grounded, an NPN transistor 12 having a base connected to the base of the NPN transistor 11, a collector connected to the base and the collector of the NPN transistor 12 connected to the emitter , A collector connected to the collector of the NPN transistor 11, a base connected to the base of the NPN transistor 13, and an emitter grounded, and an output circuit 17. Is input terminal 1
5 and the input terminal 18 of the output circuit 17,
The collector of the transistor 13 is connected to the input terminal 16 and the input terminal 19 of the output circuit 17, and the NPN transistor 1
The ratio of the area of the emitter region of the NPN transistor 11 to the area of the emitter region of the NPN transistor 11 and the ratio of the area of the emitter region of the NPN transistor 14 to the area of the emitter region of the NPN transistor 13 each have a value greater than 1. It has a configuration.

In the current comparator thus configured, the NPN transistor 12 and the NPN transistor 11
N2 / n1 (> 1), NPN
The area ratio of the emitter regions of the transistor 14 and the NPN transistor 13 is assumed to be n4 / n3 (> 1).

First, consider the case where the input current I1 is larger than the input current I2, that is, I1> I2. At this time, the NPN transistor 11 is turned on, and the NPN transistor 12, which forms a current mirror circuit with the base common to the NPN transistor 11, attempts to flow a current of (n2 / n1) × I1, but I1> I2. Therefore, ΔI2 =
Since the current shortage ΔI2 of (n2 / n1) × I1−I2 is to be extracted from the output circuit 17, a current ΔI2 is generated. The NPN transistor 13 and the NPN transistor 14 are both off, and ΔI1 = 0.

Next, consider the case where the input current I1 is smaller than the input current I2, that is, I1 <I2. At this time, the NPN transistor 11 and the NPN transistor 12 are turned off, and the NPN transistor 13 and the NPN transistor 14 are turned on, contrary to the case described above. N
The PN transistor 14 attempts to flow a current of (n4 / n3) × I2, but since I1 <I2, ΔI1 = (n4 /
Since a current shortage ΔI1 of (n3) × I2−I1 is to be taken out from the output circuit 17, a current ΔI1 is generated. ΔI2 = 0.

Next, each of the above-mentioned transition regions → and → will be considered. The input current I1 decreases from the state of
When the current value is lower than 1 = (n1 / n2) × I2, the NPN transistor 13 is turned on → the NPN transistor 14 is turned on → the NPN transistor 11 is turned off → the NPN transistor 12 is turned off. In the case of →, when the input current I1 increases and exceeds the current value of I1 = (n4 / n3) × I2, the NPN transistor 11 is turned on → NPN
The transistor 12 is turned on → the NPN transistor 13 is turned off → the NPN transistor 14 is turned off. Since the output circuit 17 only needs to detect ΔI1 and ΔI2, the output circuit 17 can be easily realized by, for example, a circuit configuration as shown in FIG.

Referring to FIG. 2, a PNP transistor 21,
22 and the constant current sources 23, 24, and 25 constitute a well-known differential input stage. The difference between the input current ΔI1 and the input current ΔI2 is determined by an NPN transistor 26 and a constant current source 2 serving as a load.
7, the voltage is converted into a voltage to obtain an output VO. , Since ΔI2> 0 and ΔI1 = 0, PN
The P transistor 21 is turned on, so that the PNP transistor 22 and the NPN transistor 26 are turned off, and the output VO
Rises to near the power supply voltage and goes to the “H” level. Conversely, in the case of the condition of ΔI1> 0 and ΔI2 = 0, P
The NP transistor 21 is turned off, the PNP transistor 22 and the NPN transistor 26 are turned on, and the output V
O falls to the ground potential and goes to "L" level.

FIG. 3 shows input / output characteristics when the input current I2 is constant and the input current I1 is varied. As is clear from the figure, the threshold value 31 when the input current I1 increases is (n4 / n3) × I2, and the threshold value 32 when the input current I1 decreases is (n1 / n2) ×
I2 and the hysteresis width ((n4 / n3)-(n1 / n
2) It has a hysteresis characteristic of × I2.

In the above-described embodiment, the case where four NPN transistors are used has been described.
The present invention is not limited to this, and can be replaced with a PNP transistor, so that the present invention can be applied not only to the case where the input current flows but also to the case where the input current flows.

[0017]

As described above, according to the present invention, since the circuit configuration is simple and the number of parts is small, an extremely excellent effect that power consumption is small and an IC can be easily realized can be obtained. In addition, since the circuit is a basic component of a current mirror circuit utilizing the matching between elements, temperature fluctuation,
An extremely excellent effect that the input current range is widened and stable against power supply fluctuation can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration according to an embodiment of a current comparator according to the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration of the output circuit of FIG.

FIG. 3 is a diagram showing input / output characteristics of an embodiment of the current comparator according to the present invention.

FIG. 4 is a circuit diagram showing a circuit configuration of a conventional current comparator.

FIG. 5 is a circuit diagram showing a circuit configuration of a current-voltage conversion circuit of a conventional current comparator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 NPN transistor 12 NPN transistor 13 NPN transistor 14 NPN transistor 15 Input terminal 16 Input terminal 17 Output circuit 18 Input terminal of output circuit 17 19 Input terminal of output circuit 17 20 Output terminal 31 Threshold 32 Threshold

Claims (1)

(57) [Claims] 1. A first transistor having a collector and a base connected to each other and having an emitter grounded, a second transistor having a base connected to the base of the first transistor and having an emitter grounded, and a collector connected to the first transistor. A third transistor connected to the base and having the emitter grounded;
A base connected to the base of the third transistor;
A fourth transistor having an emitter grounded;
A first input terminal to which the collector of the transistor is connected to the collector of the fourth transistor; and a second input terminal to which the collector of the second transistor and the collector of the third transistor are connected. , A first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is connected to the first input terminal, and the second input terminal is connected to the second input terminal. An output circuit having an output terminal connected to an output terminal, wherein a ratio of an area of an emitter region of the second transistor to an area of an emitter region of the first transistor is determined. A current comparator, wherein the ratio of the area of the region to the emitter region of the third transistor is greater than one.