JPH0436661A - Window comparator - Google Patents

Abstract

PURPOSE:To eliminate an irregularity in oscillation starting voltage and stabilize the voltage by applying the collector voltages of two transistors(TR) which are divided by resistances, to two input terminals as base inputs. CONSTITUTION:A TR T6 is connected between an input terminal A5 and an earth point G through collector resistances R9 and R10 and a voltage which is divided by the resistances R9 and R10 is inputted to the base of a TR T4. This TR T4 is connected between a power source E and an input terminal A4 through a collector resistance R7, the collector of a TR T5 is connected to the base of the TR T6, and its collector output is inputted to the base of the TR T6. Then only when an input voltage applied between the terminals A4 and A5 is in a desired range, an oscillation output is generated and when the voltage drops or rises from the desired range, the circuit oscillation is stopped, so the voltage with which the oscillating operation can be carried on has an upper limit and a lower limit, the irregularity of the oscillation starting voltage is eliminated, and the voltage can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fail-safe window comparator composed of a resistor and a transistor.

<Conventional technology> In fields that require a high degree of fail-safety, such as railway signal systems and nuclear reactor control systems, output is generated only in a specific input range, and circuit breakage, short circuit failures, etc. In such cases, level detectors with asymmetric pressure cover turns are used. The present invention relates to a window comparator that is suitable as such a level detector and also suitable as a logic operation oscillator used in a fail-safe logic circuit.

Logic operation oscillators composed of resistors and transistors are known as ``Fail-safe logic circuits using resistive semiconductor oscillators'' (IEICE Kenshu Sho 43-1), and
It is disclosed in Japanese Patent No.-29054, etc., and is already known.

Figure 1 shows an example of a logic operation oscillator clarified by these publications, in which transistors T1 and T2 are directly connected, and the collector of transistor T2 is connected to the base of transistor T3 via a Zener diode ZD. Zener diode ZD2 and resistor R connected in series to the collector of transistor T3.
3 is connected to the transistor T0 via the resistor R4.
This is to return it to its base. In addition, RI,
R2 is a collector resistance, and A, ~A are input terminals. The number of input terminals A and -A3 may be any number, or they may be made independent of each other and used as AND gates with the same number of terminals.
Or they can be connected in common.

In the logic operation oscillator having the above circuit configuration, the Zener voltages vz, vz2 of the input terminals A1 to A3 sufficient to operate the transistors T and T3, that is, the Zener diodes ZD and ZD2, are equal to the power supply voltage. When an input terminal such that VZ+ >E and VZ2 <E is input with respect to E, the transistor Tl-73 sequentially repeats on and off operations, and the output terminal v0 has an input terminal level that is approximately equal to the input terminal level given to the input terminal A3. An oscillation output that oscillates between the zero level and the zero level is obtained. On the other hand, if the input terminals applied to input terminals A, ~A, do not reach a sufficient level to operate the transistors T1 to T3, or if a disconnection failure occurs in the circuit, oscillation occurs. Therefore, it is possible to detect abnormalities in the circuit and whether the input terminal is suitable or not based on the presence or absence of oscillation output. Because of these features, the oscillator shown in FIG. 1 is increasingly being used as a component of systems that strongly require fail-safe properties, such as railway signal systems and nuclear reactor systems, particularly as level detectors.

By the way, the above-mentioned logical operation oscillator has input terminals A1 to A
If the input terminal applied to 3 rises above the operating voltage, the oscillation operation will follow this and no upper limit will occur, so it cannot be used as a level detector to detect the upper limit level. .

FIG. 2 shows an example of a window comparator circuit that improves this point and has upper and lower limits for the input level at which circuit oscillation occurs. In this window comparator, the Zener diode ZD shown in Fig.
2 is replaced by a resistor R5. R6 is a resistor inserted between the collector of transistor 71 and the base of transistor T.

In the window comparator described above, if the feedback voltage taken out from the connection point a between the collector resistor R8 and the resistor R6 of the transistor T is Vf, then this feedback voltage Vf
is R4) R3, Rs is the input voltage v3 of input terminal A3, and Vf-(R5/(R3+85))V
3.--(1). That is, the feedback voltage Vf rises and falls in proportion to the input terminal V.

The input voltage of input terminals A, ~A, is applied to transistors T1~T.
When the minimum level for operating the transistor T3 is reached, the transistor T3 enters the active region and an oscillating operation is carried out by the same circuit action as shown in Fig. 1, and the output terminal ■
. The oscillation output is extracted from.

However, when the input terminal voltage further rises and the feedback voltage Vf rises accordingly, the transistor T3 does not turn off and continues to turn on even though the transistor T3 is on. Therefore, the oscillation operation cannot be continued, and there is an upper limit to the input voltage that can be oscillated. That is, a window comparator is realized that has upper and lower limits on the input level at which circuit oscillation occurs.

<Problems to be Solved by the Invention> However, the logic operation oscillators shown in FIGS. 1 and 2 described above have the following drawbacks because the input level for starting oscillation is determined by the Zener diode ZD or ZD2. there were.

(A) Due to the non-uniformity of the Zener diode, the oscillation start voltage of each oscillator is not constant and becomes non-uniform.

(B) Since the oscillation start voltage depends on the Zener voltage,
The degree of freedom in adjusting and setting the oscillation start voltage is extremely limited.

An object of the present invention is to provide a window comparator which eliminates the above-mentioned drawbacks, stabilizes the oscillation start voltage, and allows the oscillation start voltage to be adjusted freely.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the window comparator according to the present invention includes: between the first input terminal and one end side of the power supply;
A first transistor connected via a collector resistor divided into at least two parts; a voltage divided by the collector resistor of the first transistor is used as a base input; a second transistor connected to the input terminal via a collector resistor; a resistor that divides the collector voltage of the second transistor between the power supply; and a base input voltage that divides the voltage divided by the resistor. and a third transistor connected between the one end and the other end of the power source and having a complementary relationship with the second transistor, the first input terminal and the second The oscillating operation is performed when the voltage value input to the input terminal is within a predetermined range, and the oscillating operation is stopped when the voltage value exceeds an upper limit value or a lower limit value, and a response is taken from the collector side of the first transistor. The invention is characterized in that it comprises an oscillation circuit that extracts an oscillation output.

<Embodiment> FIG. 3 is an electrical circuit diagram of a window comparator according to the present invention. In this example, the output stage transistor T
Reference numeral 6 is of the NPN type, and is connected between the input terminal Al and the ground G of the power source E via collector resistors R, , R, , which are divided into two.

The connection point between the collector resistor R9 and RIG is the feedback resistor R
+3 to the base of the transistor T4, thereby forming a collector resistor R,,R,.

The voltage divided by T4 is input to the base of transistor T4. Transistor T4 is connected between the hot side of power supply E and input terminal A4 via collector resistor R7.

A series circuit of resistors R11 and R12 is connected between the collector of the transistor T4 and the power supply ground G, and the collector voltage of the transistor T4 is divided by the resistors R11 and R12.

The base of a PNP transistor T5 is connected to the connection point C between the resistor a l and R12. This transistor T is connected between the hot side of the power supply E and the ground G.
are connected via a collector resistor R8, and two transistors T4. It is complementary to T6. Further, the collector of the transistor T is connected to the base of the transistor T6, and the collector output of the transistor T is connected to the base of the transistor T6.
6 as the base input.

The above embodiment is a circuit example in which the input polarity to the input terminals A 4 and A % is positive, and when the input polarity is negative, the NPN transistor T
,, T6 is PNP type, and PNP type transistor T
Just replace s with NPN type.

Next, the operation will be explained.

Input voltage ■4, V5 applied to input terminals A4, As is (R+z/(R11''R12 in R7))V4<E...
・(1) νt−(R+o/(Ro◆Rho))Vs<
E...To the extent that the condition (2) can be satisfied,
Since the transistors T, , T, are kept on and the transistor T4 is kept off, circuit oscillation does not occur and the output terminal V. The output voltage of is maintained at approximately zero level.

Next, the input voltage v4 of the input terminal A4 is applied to the transistor T
If the value increases to the value that can be checked with 5 turned off, that is, (Rx2/(Ry+R++”R+2))V4>E ・・
- In the range where the condition (3) can be satisfied, the transistors T, , T are turned off, and then the transistor T4 is turned on. When the transistor T4 is turned on, the transistors T s and Ta are turned on, so the transistor T4 is turned off, and the off operation of the transistor T4 turns on the transistors Ts and Ts.

As a result, an oscillation output that oscillates between the input voltage V applied to the input terminal A and substantially zero level is obtained at the output terminal v0.

Furthermore, the input voltage V of the input terminal A increases, and Vf-(
R+o/(Re”Rho))Vs>E...(4)
When the condition can be satisfied, the transistor "r
Since the base and emitter of the transistor T4 are reverse biased by the feedback voltage Vf when s and Tg are turned on, the transistor T4 is turned off. As a result, the transistors Ts and Ts are kept in the on state, and
Since the transistor T4 remains in the off state, no circuit oscillation occurs and the output terminal V. The output voltage of is fixed at approximately zero level.

That is, the window comparator according to the present invention has input voltages v4 and v applied to the input terminals A4 and As.
5 produces an oscillating output only when it is within a range that satisfies equations (2) and (3), and when the input voltage V4 drops to a range that satisfies equation (1), or when the input voltage V , is (4
), the circuit oscillation stops, and a lower limit and an upper limit are created for the input voltages V4 and VS that can continue the oscillation operation.

In this case, as is clear from conditional expressions (1) to (4), the lower and upper limits are the resistances (R7, all, R+2), (
Since the oscillation start voltage is determined depending on the values of Re, Rho), there is no non-uniformity in the oscillation start voltage unlike when a conventional Zener diode is used, and the oscillation start voltage is stable. Further, by appropriately selecting the resistance value, the oscillation start voltage can be freely set.

By the way, in general, a level detector may not have a hysteresis characteristic by changing the input level at the start and end of oscillation. A window comparator with such hysteresis characteristics can be realized by adding a circuit configuration that rectifies the output of the window comparator having the configuration shown in Figure 's3 and returns this rectified output to the input through a resistor, etc. can. Fourth
The figure is a specific circuit diagram. In the figure, 3, D,
is a numerical rectifier circuit, in which the oscillation output of the transistor T6 is negatively rectified and smoothed, and then passed through the resistor RI.
4 to the input terminal A5, and after positive rectification and smoothing in the rectifier circuit D2, the resistor R1! 1 to the input terminal A4.

In the above circuit, the input voltage v applied to the input terminal A4
4 rises and the circuit oscillates, the oscillation output is rectified by the rectifier circuit D2 and output as a positive DC voltage. This rectified output is passed through the feedback resistor RI5 to the input terminal A.
Since it is fed back to the 4 side, the input terminal at input terminal A4 rises further. On the other hand, when the input terminal V4 applied to the input terminal A4 decreases in the state of oscillating operation, 1,
The oscillation operation becomes difficult to stop because of the DC rectified output that is fed back via the feedback resistor R15. In other words, a difference is generated between the oscillation start level and the stop level, and a hysteresis characteristic is obtained.

Furthermore, when the input voltage V5 applied to the input terminal A increases and the oscillation of the circuit attempts to stop, the input terminal V increases by the effect of the negative rectified output of the rectifier circuit D1 fed back via the resistor R84. It rises and helps stop oscillation. On the contrary, when the input terminal v5 decreases, the output is applied negatively via the feedback resistor R14 due to the start of oscillation, so that oscillation is promoted. That is, even at the upper limit, there is a difference between the oscillation stop level and the oscillation start level, so a hysteresis characteristic is obtained.

Note that the transistors T4 to T6 are PNP type or NPN type.
It goes without saying that if the circuit configuration is such that a negative input voltage is supplied to the input terminals A4 and As, the rectifier circuits D2 will also have the opposite polarity.

<Effects of the Invention> As described above, the window comparator according to the present invention provides the following effects.

(a) The Zener diode that determines the oscillation start voltage in conventional logical operation oscillators has been replaced with a resistor divider, and the input gate transistor has been replaced with a complementary transistor that uses its own power source as its input power source, making it possible to oscillate. It is possible to eliminate non-uniformity of the starting voltage and stabilize it.

(b) When using a Zener diode, the oscillation start voltage is determined by the Zener voltage, so the degree of freedom is extremely narrow; however, in the case of the present invention, by appropriately selecting the resistance division ratio, Oscillation start voltage can be set freely.

(C) The window comparator according to the present invention can be used not only in level detectors but also in the technical field of fail-safe information processing. When a fail-safe window comparator is used, the restrictions on the analog processing circuit in the preceding stage are significantly relaxed, and the degree of freedom in the circuit is greatly increased. This window comparator also serves as a basic component of binary-to-ternary conversion.

(d) As a conventional window comparator, there is a method in which alternating current is superimposed on direct current input and received by a Schmitt circuit, but this method has extremely poor accuracy and has a complicated circuit configuration to be used as a level detector. be forced to. On the other hand, since the window comparator according to the present invention is based on an arithmetic oscillator, excellent effects such as high precision in each stage and a simple circuit configuration can be obtained.

(e) As shown in the example, by rectifying the oscillation output and feeding it back to the input terminal via a feedback resistor, hysteresis characteristics are provided at the start and stop of oscillation, making it possible to create a window that is very suitable as a level detector. A comparator can be realized.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of a conventional logic operation oscillator, FIG. 2 is an electrical circuit diagram of a conventional window comparator, FIG. 3 is an electrical circuit diagram of a window comparator according to the present invention, and FIG. 4 is an electrical circuit diagram of a conventional window comparator. FIG. 3 is an electrical circuit diagram in an example. T4, Ts, T6...Transistor E...Power supply R7-R15...Resistor A4. As...Input terminal Figure 1 Figure 2

Claims (2)

[Claims] (1) A first transistor connected between the first input terminal and one end of the power supply via a collector resistor divided into at least two parts, and divided by the collector resistor of the first transistor. A second transistor is connected between the other end of the power supply and a second input terminal via a collector resistor, and the collector voltage of the second transistor is connected to the power supply. and a voltage divided by this resistance as a base input, connected between the one end side and the other end side of the power supply, and in a complementary relationship with the second transistor. a third transistor, which performs an oscillating operation when the voltage value input to the first input terminal and the second input terminal is within a predetermined range, and when the voltage value exceeds an upper limit value or a lower limit value. 1. A window comparator comprising an oscillation circuit that stops oscillation when the first transistor oscillates and takes out the corresponding oscillation output from the collector side of the first transistor. (2) The oscillation start voltage and the oscillation stop voltage are made different by rectifying the oscillation output and feeding back the rectified output to the input via a feedback resistor. The window comparator mentioned.