JPH0564486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a hysteresis comparator having hysteresis characteristics. More specifically, the present invention relates to a hysteresis comparator that has a small number of elements, has a simple configuration, and is suitable for integration into an IC.

[Prior art]

FIG. 1a is a connection diagram showing an example of a conventional hysteresis comparator, and FIG. 1b is a diagram of hysteresis characteristics realized by this comparator.

This comparator has a power supply terminal 1, a common terminal 2, input terminals 3, 4 to which two input signals to be compared are applied, and an output terminal 5, and consists of transistors _Q1 to _Q5 and a diode _D1 . Differential amplifier, diodes D ₂ , D ₃ , transistors Q ₇ , Q ₉
It is composed of two sets of current mirror circuits, an output transistor _Q8 , and current circuits _I1 to _I4 .

In the diagram shown in Figure b, the horizontal axis represents the potential _V3 of the terminal 3, and the point where _V3 becomes equal to the potential of the terminal 4 is _V4 . Furthermore, the vertical axis shows the on/off state of the output transistor _Q8 .

The potential V ₃ of input terminal 3 is the potential V 4 of input terminal ₄
When the potential is lower, the output terminal 5 (output transistor Q ₈ ) is turned off, and when V ₃ becomes higher than V ₄ , the voltage shifts to point B, and the output terminal 5 is turned on.

In the figure a, _a resistor R ₂ receives constant currents i _{2 ,}
i ₃ is flowing and the base potential of transistor Q ₃
V _BQ3 is as shown in equation (1).

V _BQ3 = V ₄ + V _BEQ4 + R ₂ (i ₂ + i ₃ ) ...(1) However, V _BEQ4 is the base-emitter voltage of transistor Q _4. On the other hand, the base potential of transistor Q ₂ , V _BQ2 , is
As shown in equation (2).

V _BQ2 = V ₃ + V _BEQ1 + R ₁ i ₄ ...(2) However, V _BEQ1 is the base-emitter voltage i ₄ of the transistor Q _1. The constant current V ₃ from the constant current source I ₄ is higher than the potential of V ₄ . When moving to point B of b, transistor Q ₈
turns on. This means that, as with a normal comparator, from equations (1) and (2), at the point where V _BQ3 = V _BQ2 , the transistor Q ₈ changes from off to on.

At this time, in FIG. 1b, the hysteresis width is 2
Using the condition of V _BQ3 = V _BQ2 from equations (1) and (2), V ₃ −V ₄ =V _BEQ4 +R ₂ (i ₂ +i ₃ ) −V _BEQ1 −R ₁ i ₄ ...(3) becomes. In equation (3), if V _BEQ4 V _BEQ1 , V ₃ − V ₄ = R ₂ (i ₂ + i ₃ ) − R ₁ i ₄ ...(4), and the hysteresis width 2 is the resistance R ₁ , R ₂ and constant currents i ₂ , i ₃ , i ₄ of constant current sources I ₂ , I ₃ , I ₄ .

Similarly, V ₃ is again at a lower potential than V ₄ and b
When moving to point B, when transistor _Q8 changes from on state to off state (in this state, transistor
Q ₆ is also off and constant current i ₃ flows through diode D ₂ )
, V _BQ3 and V _BQ2 are as shown in equations (5) and (6).

V _BQ3 = V ₄ + V _BEQ4 + R ₂ i ₂ ... (5) V _BQ2 = V ₃ + V _BEQ1 + R ₁ , i ₄ ... (6) From formulas (5) and (6), hysteresis width 1 is V _BQ3 = V _{BQ2
Using the conditions of _ _ _ _ _ _} becomes.

V ₄ −V ₃ =R ₁ i ₄ −R ₂ i ₂ ...(8) Therefore, the hysteresis width 1 is the resistance R ₁ , R ₂ ,
Determined by constant currents i ₂ and i ₄ .

Therefore, the hysteresis width of this entire circuit is
The sum of hysteresis width 1 and hysteresis width 2 is expressed by equation (9) from equations (4) and (8).

Hysteresis width 1 + Hysteresis width 2 = R ₂・i ₃
...(9) In the conventional example of such a circuit configuration, in order to obtain the hysteresis characteristic with the hysteresis width expressed by equation (9), two resistors, two sets of current mirror circuits, and a circuit for determining the hysteresis width are required. 3 current sources,
Transistor _Q6 is required to control current _i3 , which increases the number of elements to configure the circuit.
The structure was complicated.

[Object of the present invention]

The present invention has been made to solve these drawbacks of conventional circuits, and aims to realize a hysteresis comparator with a small number of elements and a simple configuration.

[Summary of the invention]

A hysteresis comparator of the present invention for achieving the above-mentioned object is a comparator comprising a power supply terminal, a common terminal, first and second input terminals, and an output terminal, and configured by a differential amplifier. , A series circuit of a first constant current source, a forward diode, and a second constant current source is connected between the power supply terminal and the common terminal, and the base is connected to the output stage of the differential amplifier. A collector of the transistor is connected to a connection point between the first constant current source and the diode, an emitter is connected to the common terminal, and one input terminal of the differential amplifier is connected to the first input terminal. , a connection point between the diode and the second constant current source is connected to the other input terminal of the differential amplifier and also connected to the second input terminal via a resistor. That is, the circuit according to the present invention includes a first constant current source in which a circuit for determining the hysteresis width is connected in series between the power supply terminal and the common terminal;
a diode, a second constant current source, a transistor connected between the connection point between the first constant current source and the diode and the common terminal, and a transistor connected between the connection point between the diode and the second constant current source and the input terminal. It consists of a resistor. Therefore, in the hysteresis comparator of the present invention, the hysteresis width is substantially determined by the product of the resistance value of the resistor and the current value of the first constant current source. The three elements that greatly affect the hysteresis width are the first and second constant current sources and the resistor, and the conventional current mirror circuit is not required and the number of constant current sources and transistors can be reduced. .

〔Example〕

FIG. 2a is a connection diagram showing an example of a hysteresis comparator according to the present invention, and FIG. 2b is a diagram of hysteresis characteristics realized by this comparator.

In this figure, 1 is the power supply terminal to which the power supply E ₀ is connected, 2 is the common terminal, 3 is the input terminal to which one input signal E ₂ to be compared is applied, and 4 is the input terminal to which the other input signal E ₁ is applied. 5 is an input terminal to which a comparison result is output.

Transistors Q ₁₁ to Q ₁₃ constitute a differential amplifier,
Current source I ₁₂ , I ₁₃ transistor Q ₁₄ , diode D ₁₁
and a resistor R constitute a circuit for determining the hysteresis width. In this circuit for determining the hysteresis width, a constant current source I ₁₃ and a diode D ₁₁
and constant current source _I12 are connected in series with each other and between power supply terminal 1 and common terminal 2. In addition, the collector of the transistor Q ₁₄ is connected to the connection point between the constant current source I ₁₃ and the diode D ₁₁ , the emitter is connected to the common terminal 2, and the base is connected to the collector of the transistor Q ₁₃ and the output transistor corresponding to the output terminal of the differential amplifier. Each is connected to the base of Q ₁₅ . The connection point between the diode D ₁₁ and the constant current source I ₁₂ is connected to one input terminal 4 via a resistor R, and
One transistor that makes up the differential amplifier
Connected to the base of Q ₁₂ .

In such a connection, when the input signal _E2 applied to terminal 3 is at point A (see Figure 2b), which is lower than the input signal (reference voltage) _E1 applied to terminal 4, the output transistor Q ₁₅ is in the off state. At this time, the transistor Q ₁₄ is also in an off state, and the constant current i ₁₃ from the constant current source I ₁₃ is divided into the resistor R side and the constant current source I ₁₂ side via the diode D ₁₁ . Therefore, the base potential of transistor _Q12
V _BQ12 is as shown in equation (10).

V _BQ12 = E ₁ + R (i ₁₃ − i ₁₂ ) ...(10) When the input signal E ₂ moves from point A to the point where it becomes the same as the reference voltage E ₁ to a higher voltage point B, the output transistor Q ₁₅ changes from off state to on state. The difference between the voltage of E ₂ and E ₁ at this point of change becomes the hysteresis width 2. Such a change occurs when the base potentials V _BQ11 and V _BQ12 of transistors Q ₁₁ and Q ₁₂ become equal.

V _BQ11 of the transistor Q ₁₁ is equal to the input signal E ₂ applied to the input terminal 3, and is expressed by equation (11).

V _BQ11 = E ₂ ...(11) From equations (10) and (11), using the condition of V _BQ11 = V _BQ12 ,
Equation (12) is obtained.

E ₂ - E ₁ = R (i ₁₃ - i ₁₂ ) ...(12) Therefore, as is clear from equation (12), the value of hysteresis width 2 is the difference between resistance R and currents i ₁₃ and i ₁₂ (i ₁₃ −
i ₁₂ ).

When the output transistor Q ₁₅ turns on, the transistor Q ₁₄ also turns on, so that the current i ₁₃ from the constant current source I ₁₃ flows to the transistor Q ₁₄ side and no longer flows to the diode D ₁₁ side. Furthermore, when the transistor Q ₁₄ is turned on, the diode D ₁₁ is reverse biased, so it is turned off, and the potential on the cathode side of the diode D ₁₁ , that is, the base potential V _BQ12 of the transistor Q ₁₂ is
The potential changes from the value shown by equation (10) to an even lower potential V _BQ12 ' shown by equation (13).

V _BQ12 ′=E ₁ −Ri ₁₂ (13) From this state, when the input signal E ₂ decreases again toward point A, the transistor Q ₁₅ changes from on to off. The difference between E ₁ and E ₂ at these changing points is the hysteresis width 1. This hysteresis width 1
From equations (11) and (13), using the condition of V _BQ11 = V _BQ12 ′, becomes as shown in equation (14).

E ₁ −E ₂ = Ri ₁₂ ...(14) From this, the hysteresis width of the entire circuit is (12)
From equation (14), hysteresis width 1 + hysteresis width 2 = R (i ₁₃ - i ₁₂ ) + Ri ₁₂ = Ri ₁₃ ... (15), which is determined by the product of resistance R and constant current i ₁₃ , and the first The same characteristics as the conventional circuit shown in the figure can be obtained.

In particular, ICs with unadjusted hysteresis comparators
According to the conventional circuit, there are five elements that greatly affect the hysteresis width: constant current sources I ₂ , I ₃ , I ₄ and resistors R ₁ and R ₂ made up of transistors, etc. The circuit according to the present invention has three elements, constant current sources I ₁₂ and I ₁₃ , and resistor R, and there are fewer elements that greatly affect the hysteresis width, so the yield is improved.

FIG. 3 is another connection diagram of the circuit according to the present invention. In this embodiment, the differential amplifier is constituted by NPN type transistors Q ₂₁ and Q ₂₂ , and the other configurations are not significantly different from those in FIG. 2a. That is, the diode D ₁₂ in FIG. 2a corresponds to the diode-connected transistor Q ₂₄ , and the transistor Q ₁₃ in FIG. 2a corresponds to the transistors Q ₂₃ and Q ₂₃ '. And the collector of transistor Q ₂₃ ′ is a transistor
It is connected to the base of _Q14 and the output is obtained through transistor _Q15 . It goes without saying that both the circuits shown in FIGS. 2a and 3 can be integrated into an IC.

[Effects of the present invention]

As explained above, according to the present invention, compared to conventional circuits, it is possible to eliminate the need for a current mirror circuit, reduce the number of constant current sources, reduce the number of transistors, etc., and therefore, the number of elements is small and the configuration is simple. A hysteresis comparator can be realized. Since the circuit of the present invention has a small number of elements, when integrated into an IC, the area of the IC can be reduced, the yield can be improved,
Since the effect of cost reduction can be expected, IC
This is particularly effective when

[Brief explanation of the drawing]

Figure 1 is the connection diagram and characteristic diagram of the conventional circuit, Figure 2
The figures are a connection diagram and a characteristic diagram of a circuit according to the present invention, and FIG. 3 is a connection diagram showing another embodiment of the present invention. 1...Power terminal, 2...Common terminal, 3, 4...
...Input terminal, 5...Output terminal, _Q11 to _Q15 ...Transistor, _I11 to _I13 ...Constant current source, _D11 ...Diode, R...Resistor.

Claims (1)

[Scope of Claims] 1. A comparator comprising a differential amplifier, comprising a power supply terminal, a common terminal, first and second input terminals, and an output terminal, wherein the power supply terminal and the common terminal Between the first
A series circuit of a constant current source, a forward diode, and a second constant current source is connected, and a collector of a transistor whose base is connected to the output stage of the differential amplifier is connected to the first constant current source. An emitter is connected to the common terminal at a connection point with the diode, one input end of the differential amplifier is connected to the first input terminal, and the diode and the second constant current source are connected to each other. A hysteresis comparator, characterized in that a connection point thereof is connected to the other input terminal of the differential amplifier and also connected to the second input terminal via a resistor.