JPS6214517A - Hysteresis comparator circuit - Google Patents

Abstract

PURPOSE:To set optionally a hysteresis width by connecting transistors TRs different in emitter area between the earth and emitters of a pair of TRs whose bases an input voltage is impressed to differentially. CONSTITUTION:A TR 12 is provided, and the collector of the TR 12 is connected to the emitter of a TR 2 and the base of a TR 4, and the base of the TR 12 is connected to the anode of a diode 9 and the base of a TR 10, and the emitter of the TR 12 is grounded. Emitter areas of TRs 10 and 12 are (n) times and (m) times as large as that of a TR 11 for constant current source. By this circuit constitution, a hysteresis width V3-V4 (V3 and V4 are base voltages of TRs 3 and 4) is not dependent upon current amplification factors of TRs but dependent upon the emitter area ratio of the TR 10 to the TR 12. The variation of the hysteresis with due to temperature can be ignored. Thus, the hysteresis width can be set to an optional value determined only by the emitter area ratio of TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a comparator circuit whose hysteresis width can be arbitrarily set.

BACKGROUND OF THE INVENTION A conventional hysteresis comparator circuit configured to utilize the base-emitter voltage (VBE) of a transistor is shown in FIG. The operating principle of the hysteresis comparator circuit will be explained below with reference to FIG.

The comparison voltages V and v2 applied to the bases of the transistors of this hysteresis comparator circuit and 2
If the relationship vl<v2 is established between them, transistors 2 and 4 are in a conductive (on) state, while transistors and 3 are in a cutoff (off) state. As a result, no current flows through the diode 5 and it is in an off state. On the other hand, current flows through the diode 7 through the transistor 4, and the transistor 8. Diode 9 and transistor.

turns on. Note that transistor 1 is a transistor for a constant current source, and a constant voltage v0 is applied to its base, and a current source is always applied to its collector.

is flowing. By the way, transistor o is a transistor whose emitter size is the same as that of transistor 1, and when it is on, the collector current is the same as that of transistor 1. is flowing.

Base voltage of transistor 3 in the above circuit state■
3 is the following formula.

■3=v1-vBE1 ”vl-vT tn (Io' Engineering)”
``''''' (1) v 'Base emitter BE1/evening voltage I8 of transistor 1: Saturation current VT of transistor 1: kT/q k: Boltzmann constant Also, the base voltage v4 of transistor 4 is calculated using the following formula % Formula % ■BE2 :Base-emitter voltage of transistor 2 hFE4: Current amplification factor of transistor 4 Therefore,
The hysteresis width of this circuit is given by v3-v4, and is given by the following equation.

V3-V4=V1-V2-VT tn(hFE4+ 1
), (3) Problems to be Solved by the Invention In the conventional hysteresis comparator circuit, there arises a disadvantage that the current amplification factor hFE O value greatly influences the hysteresis width. That is, the current amplification factor hFE of the transistor
There is a possibility that the hysteresis width may change greatly due to factors such as variations in the manufacturing process or temperature changes during operation, and it is extremely difficult to fix the hysteresis width to an arbitrary value.

Means for Solving the Problems The hysteresis comparator circuit of the present invention comprises first and second transistors whose bases are applied with an input voltage in differential form and whose collectors are connected to a power supply; The base is connected to each emitter of the transistor No. 2,
A collector-emitter circuit is provided between third and fourth transistors whose emitters are commonly connected and connected to a ground point via a constant current source transistor, and the emitters of the first and second transistors and the ground point. fifth and sixth transistors connected; and the third and fourth transistors connected to each other;
first and second diodes having their cathodes connected to the respective collectors of the transistors and their anodes connected to the power supply; their bases connected to the collectors of the third transistor; their emitters connected to the power supply; and the collectors connected to the collectors of the fourth transistor. a seventh transistor with the same polarity as the seventh transistor and whose base is connected to the collector of the fourth transistor and whose emitter is connected to the power supply, and whose collector is connected to the cathode. an eighth transistor connected to an anode of a third diode connected to a ground point, and bases of the sixth and sixth transistors are connected to a connection point between the eighth transistor and the third diode. Further, the emitter areas of the sixth and sixth transistors are set to be n times and m times the emitter area of the constant current source transistor.

Effect: According to this configuration, a comparator circuit is realized in which the current amplification factor of the transistor does not affect the hysteresis width, and the transistor emitter area ratio (n/m) is dominant in setting the hysteresis width. Ru.

Embodiment An embodiment of the hysteresis comparator circuit of the present invention is shown in FIG. 1, and its operation will be explained below with reference to this circuit.

The feature of this circuit is that a transistor 12 is added compared to the conventional example, the collector of this transistor is connected to the emitter of transistor 2 and the base of transistor 4, the base is connected to the anode of diode 9 and the base of transistor 0, The emitters are grounded, and the emitter areas of transistor o and transistor 2 are n times and m times larger than the emitter area of constant current source transistor 1. Other circuit conditions are the same as in the conventional example.

In this circuit, voltages V and ■2 are applied to the bases of the transistor and 2, and between them ■1<■2
Assuming that the following relationship holds true, at this time, transistors 2 and 4 are in an on state, while transistors and 3 are in an off state. As a result, diode 5
No current flows through the transistor 6, and the transistor 6 is also turned off. On the other hand, current flows through the diode 7 through the transistor 4, and the current flows through the transistor 8. Diode9. Transistor o and transistor 2 are turned on.

At this time, by designing the circuit so that equal voltages are applied to the bases of transistors 10, 12 and 11, transistor 1 is applied to the collector of transistor 0.
A current (n I o ) that is n times the collector current I0 of
In addition, the collector of transistor 2 receives m times the current (m
Io) is flowing.

The base voltage v3 of the transistor 3 at this time is expressed by the following equation.

v3=v1-vBEl=v1-vTtn(n engineering/I8)...(4)
1' Also, the base voltage v4 of the transistor 4 is expressed by the following formula % Formula % Therefore, the hysteresis width is determined by the following formula according to formulas (4) and (5).

V s −■4:=: v1v2−V+Zn(n/ (
rrx+ 1 / (h F E 4+ 1) ) )
・・・・・・・・・・・・ (6) The current amplification factor hFE4 of transistor 4 is normally hFE4
Since it is set to a value that satisfies the relationship ≧1oO, 1/(hFE4+1):; o −=−−(
The relationship 7) holds true.

Therefore, equation (6) becomes a simple equation as shown below.

V3-V4=V1-V2-VTtn(n/rn)--
-...-(a) Equation 8 shows that the hysteresis width does not depend on the current amplification factor hFE of the transistor, and the transistor 10
It is shown that it depends on the emitter area ratio of 12 and 12.

Also, the term of the hysteresis width due to temperature change is vTC=
Since it is only kT/(1), temperature changes can be ignored compared to the conventional comparator circuit shown in FIG.

Effects of the Invention According to the hysteresis comparator circuit of the present invention, the influence of the current amplification factor hFE of the transistor on the hysteresis width can be ignored. Therefore, even if hFE varies greatly due to variations in the manufacturing process or temperature changes, the hysteresis width does not change due to this, and the hysteresis width can be set to any value determined only by the emitter area ratio of the transistor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a hysteresis comparator according to the present invention, and FIG. 2 is a circuit diagram of a conventional hysteresis comparator. 1.2, 3, 4, 10, 11.12...npn
type transistor, 5, 7.9... diode,
6゜8...PNP type transistor.

Claims (1)

[Claims] An input voltage is applied to the bases in a differential format, the collectors are connected to a power supply, and the bases are connected to each emitter of the first and second transistors, and the emitters are commonly connected. and a third and fourth transistor connected to the ground via a constant current source transistor.
fifth and sixth transistors having collector-emitter circuits connected between the emitters of the first and second transistors and a ground point, and a cathode connected to each collector of the third and fourth transistors. have first and second diodes whose anodes are connected to a power supply, bases of which are connected to the collector of the third transistor, emitters of which are connected to the power supply, and collectors of which are connected to the collector of the fourth transistor; The transistors include a seventh transistor with complementary polarity, and a seventh transistor with the same polarity as the seventh transistor, whose base is connected to the collector of the fourth transistor, whose emitter is connected to the power supply, and whose collector has a cathode connected to the ground point. an eighth transistor connected to the anode of the third diode; bases of the fifth and sixth transistors are connected to a connection point between the eighth transistor and the third diode; and the emitter area of the sixth transistor is n of the emitter area of the constant current source transistor.
A hysteresis comparator circuit characterized in that the hysteresis comparator circuit is set to double and m times.