JPH0936715A - Comparator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a characteristic of the comparator circuit with a hysteresis characteristic from being affected by power fluctuation and to change the characteristic into a desired characteristic. SOLUTION: An on-current of a transistor(TR) Q2 is extracted by current mirror transistors(TRs) Q3 , Q6 and given to a base resistor R2 of the TR Q2 and an emitter output current of a TR Q7 whose base receives a reference voltage Vref is applied to the base resistor R2. A base voltage VA, when the TR Q2 is conductive, and a base voltage VB when the TR Q2 is nonconductive, are both independently of a power supply Vcc and dependent on the external voltage Vref.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparator circuit, and more particularly to a comparator circuit having a hysteresis circuit and having a differential circuit configuration suitable for a semiconductor integrated circuit.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration example of a conventional comparator circuit of this type. The transistors Q1 and Q2 are differential pair transistors whose emitters are commonly connected to each other. The input signal IN is supplied to the base of the transistor Q1. The base of the transistor Q2 has a reference voltage (VA or VB) as a threshold value of this comparator circuit. ) Is being applied,
Therefore, the resistor R2 is connected between the base of the transistor Q2 and the ground potential.

A resistor R1 is connected between the collector of the transistor Q1 and the power supply Vcc and the transistor Q1 is connected.
By commonly connecting the collector of 1 and the base of the transistor Q2, the reference voltage, which is the threshold value of the comparator circuit, changes to VA or VB, and a so-called hysteresis characteristic is exhibited. The operation will be described later.

The collector current of the transistor Q2 is taken out by the current mirror circuit composed of the transistors Q3 and Q4 and supplied to the resistor R3. The voltage generated in the resistor R3 is input to the base of the output transistor Q5, and the output OUT is derived from the collector load R4.

A voltage of VA = R2Vcc / (R1 + R2) is initially applied to the base of the transistor Q2 as a threshold voltage VA. In this state, when the input signal IN is supplied to the base of the transistor Q1 and the base of the transistor Q1 exceeds the base voltage VA of the transistor Q2, the transistor Q1 is turned on and the current Ib is supplied to the resistor R2 via the resistor R1. Flowing.

As a result, the base potential of the transistor Q2 changes, and it drops to VB = Vcc-I0.R1. Here, I0 indicates the current value of the constant current source of the differential circuit. This transistor Q2
The change in the base potential of changes the switching characteristic of the comparator circuit, resulting in a comparator circuit having a hysteresis characteristic.

[0007]

In the conventional comparator circuit of this type shown in FIG. 2, since the threshold voltage VB depends on the power supply voltage Vcc, the hysteresis characteristic of the comparator circuit changes when the value of this Vcc changes. There is a drawback that. There is also a problem that the hysteresis characteristic cannot be controlled as desired.

An object of the present invention is to provide a comparator circuit that can obtain stable characteristics without changing hysteresis characteristics with respect to power supply fluctuations.

Another object of the present invention is to provide a comparator circuit which can control the change of the hysteresis characteristic as desired.

[0010]

According to the present invention, there is provided a pair of first and second transistors having a differential connection structure, an input signal is supplied to the base of the first transistor, and A comparator circuit in which a reference voltage is supplied to the base of a second transistor, wherein a base bias resistance element connected between the base of the second transistor and a reference potential point, and A second current supply means for supplying a current equal to a collector current of the second transistor when the second transistor is conductive, and a second current supply means for supplying a current proportional to a predetermined reference voltage to the resistance element. A comparator circuit that does

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The operation of the present invention is as follows.
That is, a resistance element is provided between the base of the transistor to which the reference voltage is applied to the base and the reference potential point, and the current flowing through the resistance element is made a current proportional to the external voltage irrelevant to the power supply Vcc. Of. This allows
It is possible to obtain a hysteresis characteristic which does not depend on the power source Vcc and can be changed freely by an external voltage.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. The input signal IN is supplied to the base of the differential pair transistor Q1, and the resistor R2 is connected between the base of the transistor Q2 and the ground potential.

The resistor R2 has a collector current (I) when the transistor Q2 is turned on.
0) is taken out and supplied by a current mirror circuit composed of transistors Q3 and Q6. Further, the emitter current of the transistor Q7 is supplied to the resistor R2 via the resistor R5.

A reference voltage Vref is externally supplied to the base of the transistor Q7, and its collector is a power supply Vref.
Connected to cc.

The other structure is the same as that of FIG. 2 and its explanation is omitted.

In such a structure, when the input signal IN is not applied, the transistor Q2 is turned on, and its collector current I0 is taken out by the current mirror circuit of the transistors Q3 and Q6 and flows to the resistor R2. A constant current from the transistor Q7 also flows through the resistor R2.

Therefore, the base voltage VA of the transistor Q2 at this time is VA = I0.R2 + (Vref-VBE) .R2 / (R2 +
R5). VBE is the base-emitter voltage of the transistor Q7.

In this state, the input signal IN is applied and V
When A is exceeded, the transistor Q7 is turned off, so that only a constant current from the transistor Q7 flows through the resistor R2.

As a result, the base voltage of the transistor Q2 drops to VB = (Vref-VBE) .multidot.R2 / (R2 + R5). Therefore, hysteresis characteristics are possible.

As is clear from the above equation, VB in this case does not depend on the power supply voltage Vcc, so that even if Vcc fluctuates, there is no effect on the characteristics. In addition, the reference voltage Vre from the outside
By changing f as desired, the hysteresis characteristic (VB
) Can be changed. Although the NPN transistor is used in the above embodiment, it is obvious that the PNP transistor may be used.

[0022]

As described above, according to the present invention, the threshold value of the comparator does not depend on the power supply voltage but depends on the reference voltage from the outside. This has the effect of obtaining a comparator circuit that can be set to, and is suitable for semiconductor integrated circuits.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a circuit example of a conventional comparator.

[Explanation of symbols]

 Q1, Q2 Differential pair transistor Q3, Q4, Q6 Current mirror transistor Q5 Output transistor Q7 Emitter follower transistor R2-R5 Resistance element

Claims (4)

[Claims] 1. A pair of first and second transistors having a differential connection configuration, wherein an input signal is supplied to the base of the first transistor and a reference voltage is supplied to the base of the second transistor. A supplied comparator circuit, which includes a base bias resistance element connected between the base of the second transistor and a reference potential point, and a collector current for the resistance element when the second transistor is conductive. A comparator circuit comprising: a first current supply means for supplying an equal current and a second current supply means for supplying a current proportional to a predetermined reference voltage to the resistance element. 2. The first current supply means is a current mirror circuit which is connected to the collector of the second transistor and supplies the collector current to the resistance element. Comparator circuit. 3. The second current supply means has a transistor to the base of which the predetermined reference potential is supplied, and the emitter current of the transistor is supplied to the resistance element. A comparator circuit according to item 1 or 2. 4. The comparator circuit according to claim 3, wherein the emitter current is configured to be supplied to the base bias resistance element via a second resistance element.