JPH0654870B2 - AND circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fail-safe AND circuit, such as an AND circuit used in a railway signal processing device,
In particular, the present invention relates to a fail-safe logical product circuit including an AND logical operation oscillator, an amplifier that amplifies its output, and a rectifying circuit that rectifies its output.

2. Description of the Related Art A logical product circuit including a logical product operation oscillator using a threshold oscillator, an amplifier for amplifying its output, and a rectifying circuit for rectifying its output is disclosed in, for example, Japanese Patent Publication No. 43-1254.
No. 8, Japanese Patent Publication No. 45-29054, Japanese Patent Publication No. 51
Various proposals have been made such as the -38211 publication. These known circuits are characterized in that the logical product operation oscillator and the amplifier which form the logical product circuit are used as a common power source, and the logical product circuits for performing logical operation are coupled by a rectifier circuit. . However, in the conventional logical operation circuit of this type, when the logical product operation oscillator is configured to oscillate when a signal of a level within the frame of the power supply voltage (potential within the power supply frame) is input, the amplifier and the rectifier circuit are provided. When the capacitor for AC coupling is short-circuited, the power supply voltage of the AND circuit is directly generated at the output of the rectifier circuit, and as a result, the AND operation oscillator of the next stage oscillates.

Therefore, in the conventional logical operation circuit of this type, in order to make the circuit fail-safe, the oscillation start potential of the logical product operation oscillator is set higher than the power supply potential (the power supply potential is outside the frame). Means have been taken to make the rectifier circuit an n-fold voltage rectifier circuit whose output is clamped to the power supply potential. However, according to this method, for example, in order to use a certain binary processed output as an input to this operational oscillator, the processed output must be converted to a level lower than the oscillation start voltage of the operational oscillator, and this Another oscillator must be oscillated by the converted output signal, and its output must be converted into a signal of the potential outside the power supply frame by the rectification to be used as an input signal to the operational oscillator (otherwise the logical product operational oscillator will not oscillate) Had.

An object of the present invention is to provide a fail-safe AND circuit which can set the oscillation start voltage of a logical product operation oscillator to a potential within the power supply frame and does not need to clamp the output of the rectifier circuit to the power supply potential. With the goal.

In order to achieve the above object, the present invention has a window comparator / logical product operation oscillator having threshold values above and below an input signal and not oscillating when a circuit element fails and the window comparator / logical product operation. An AND circuit is configured by using an amplifier that amplifies the output signal of the oscillator and a rectifier circuit, and the upper threshold of the window comparator / AND operation oscillator is set to be lower than the power supply potential of the amplifier. It is characterized in that the upper limit threshold value of the window comparator / logical product operation oscillator can be set to a level lower than the power supply potential of the amplifier.

EXAMPLES The present invention will be described below based on examples shown in the drawings.

FIG. 1 shows an embodiment of a two-input logical product circuit. In FIG. 1, 1 is a logical product operation oscillator which has upper and lower threshold values and does not oscillate due to a failure of a circuit element, and 2 is an output of the logical product operation oscillator 1. Is a rectifier circuit for rectifying the output of the amplifier 2. In this logical product circuit, input signals are input to the terminals T1 and T2 of the logical product operation oscillator 1, and the power supply voltage (E) for the logical product operation oscillator 1 is provided between the terminals T3 and T4.
Is applied, the power supply voltage (V) for the amplifier 2 is applied to the terminal T5, the terminal T4 is used as the ground terminal, and the signal between the output terminals T6 and T7 of the rectifier circuit 3 is used as the output of the AND circuit. As for the logical product operation oscillator 1, in FIG. 1, the same applicant as the applicant is one of the applicants.
Two window comparator circuits disclosed in Japanese Patent Publication No. 2 are cascade-connected to form a two-input window comparator AND operation oscillator. The two-input window comparator AND logical operation oscillator shown in FIG. 1 is a system in which two window comparator circuits 10 and 11 are connected in cascade and a phase inversion circuit 12 is inserted between them to oscillate. Japanese Patent Application No. 58-175 by the same person as the applicant
It has already been filed under No. 914.

Each of the window comparator circuits 10 and 11 has a window defined by upper and lower threshold levels, and a logical product operation is performed only when the levels of the input signals to the terminals T1 and T2 are within the defined range of the windows. The oscillator 1 oscillates and does not oscillate when the level of one or both of the input signals is out of the range of the window or when the circuit fails, so that the output signal becomes zero with respect to the circuit failure. It is a known circuit having a characteristic of asymmetrical error.

Each window comparator circuit 10, 11 has three transistors Q1, Q2, Q3 or Q5, Q6, Q7 connected in series and eight resistors R1, R2, R3, R4, R5, R6 in the illustrated example. ,
R7, R8 or R11, R12, R13, R14, R15, R16, R
It is composed of 17 and R18. Transistors Q2 and Q1,
Q3 and Q6, and Q5 and Q7 are complementary transistors, and here, Q2 and Q6 play the role of an amplifier having a power supply potential (E).

The output of the transistor Q7 of the window comparator circuit 11 is divided by collector resistors R16 and R17 and input to the base of the transistor Q1 of the window comparator circuit 10. The output of the transistor Q1 is input to the base of the transistor Q2 by the resistors R2 and R3. The voltage is input including the level shift of the power input to the terminal T3, and the output of the transistor Q2 is input to the base of the transistor Q3 after being divided by the resistors R4 and R5. Is divided by collector resistors R6, R7 and supplied to the phase inversion circuit 12 via the resistor R8. The window comparator circuit 10 has a power input (E) to the terminal T3, an input to the terminal T1 of I1, resistors R1, R2, R3,
Assuming that the resistance values of R6 and R7 are R1, R2, R3, R6 and R7 respectively, the condition for oscillation is (R1 + R2 + R3) E / R3 <I1 I1 <(R6 + R7) E / R7.

Where (R1 + R2 + R3) E / R3 and (R6 + R7) E / R
Reference numeral 7 is a condition of the terminal T1 for oscillating the logical product operation oscillator 1, and this threshold interval is called a window of the terminal T1. (R1 + R
2 + R3) E / R3 is the lower threshold of oscillation, (R6 + R7)
E / R7 is the upper threshold value of oscillation.

The output of the phase inverting circuit 12 is input to the base of the transistor Q5 of the window comparator circuit 11, and the output of the transistor Q5 is input to the base of the transistor Q6.
The voltage is divided and input by R13 including the level shift of the power supply input to the terminal T3, and the output of the transistor Q6 is divided and input by the resistors R14 and R15 to the base of the transistor Q7. This window comparator circuit 11
Is the power input to the terminal T3 (E), the input signal to the terminal T2 is (12), and the resistance values of the resistors R11, R12, R13, R16, R17 (R11, R12, R13, R16, R17). Then, (R11 + R12 + R13) E / R13 <I2 I2 <(R16 + R17) E / R17 is the condition for oscillation. Here, (R11 + R12 + R13) E
/ R13 and (R16 + R17) E / R17 are AND operation oscillator 1
This threshold interval is called the window of the terminal T2 under the condition of the terminal T2 for oscillating. (R11 + R12 + R13) E / R13
Is the lower threshold of oscillation, and (R16 + R17) E / R17 is the upper threshold of oscillation. The output of the window comparator circuit 11 can be the Cholesta output of the transistor Q6, for example.

The phase inversion circuit 12 includes a transistor Q4 and two resistors R9,
It is composed of R10 and. The transistor Q4 has a base connected to the output terminal of the window comparator circuit 10, a collector connected to the terminal T1 via a collector resistor R9, and a resistor R10 connected to the base of the transistor Q5 of the window comparator circuit 11. , The emitter is connected to terminal T3.

The amplifier 2 includes a coupling capacitor 20, two resistors 21 and 22 provided on the output side thereof, and an amplification transistor 23.
And a resistor 24 provided on the collector side of this transistor 23
And a transistor 25 having a base connected to the collector of the transistor 23 and a collector connected to the terminal T5, and a diode 26 provided between the collector of the transistor 23 and the emitter of the transistor 25. Output is input to the base of transistor 23 via capacitor 20 and resistor 21, and the power supply voltage (V) to terminal T5
Input to the collector of the transistor 23 via the resistor 24 and the collector of the transistor 25, the base side of the transistor 23 is connected via the resistor 22 to the terminal T4, that is, the ground potential, and the emitter of the transistor 23 is connected to the terminal T4. Connected to. The power supply voltage (V) to the terminal T5 is
The level (potential) is selected to be higher than the upper threshold value of the window of the window comparator circuits 10 and 11. In this amplifier 2, the transistors 23 and 25 are turned on and off by the oscillation output of the logical product operation oscillator 1, and the transistor 25
The voltage of the emitter of is output to the rectifier circuit 3. Therefore, the output signal of the amplifier 2 is output to each circuit element 20, 21, 22, 23, 24, 2
If either of 5 and 26 fails, either the power supply voltage (V) to the terminal T5 or the ground potential is fixed, or the output signal of the AND operation oscillation is output in the same manner as in the normal state. (When the AND operation oscillator 1 is not oscillating, it is fixed to either the power supply voltage (V) or the ground potential). This output signal is an AC output that changes between the ground potential and the potential determined by the power supply voltage (V) and the load of the rectifier circuit 3 only when the above circuit elements are normal and the AND operation oscillator 1 is oscillating. It becomes a signal (changes between approximately power supply voltage (V) and ground potential).

The rectifier circuit 3 has an output only when the output of the amplifier 2, that is, the oscillation output of the AND logical operation oscillator 1 is input, and is not output when the oscillation output is not input and a circuit failure occurs. A safe rectifying and smoothing circuit in which the input signal is clamped to ground potential using a diode 32. That is, as shown in the figure, the rectifying / smoothing circuit shown in the figure is a known voltage doubler composed of a coupling capacitor 30, two diodes 31 and 32 provided on the output side thereof, and a four-terminal capacitor 33. Rectifier circuit, not superimposed on power supply potential.

The level of the rectified output (Vout) of the rectifier circuit 3 is E only when the circuit elements 30, 31, 32, 33 are normal and a signal which changes between the ground potential and a predetermined level is input from the amplifier 2. <Vout <V, and when any of the circuit elements 30, 31, 32, and 33 causes a short circuit or disconnection fault, the power source voltage potential (V) or the ground potential is input to the terminal T5. .

In this AND circuit, the AND operation oscillator 1 has a terminal T
When the input signal I1 to 1 exceeds the upper limit threshold value, the transistor Q4 remains on, and when it does not reach the lower limit threshold value, the transistor Q2 remains on. If the input signal I2 to the terminal T2 exceeds the upper threshold value, the transistor Q1 remains on, and if it does not reach the lower threshold value, the transistor Q6.
Remains on.

However, when the input signal (I1) to the terminal T1 satisfies the oscillation condition while the input signal (I2) to the terminal T2 satisfies the oscillation condition, each of the transistors Works and oscillates. That is, Q 2 · off → Q 3 · off → Q 4 · on → Q 5 · off → Q
6 ・ OFF → Q 7 ・ OFF → Q 1 ・ ON → Q 2 ON → Q 3 ・
It oscillates in the process of ON → Q 4 ・ OFF → Q 5 ・ ON → Q 6 ・ ON → .... In addition, the input signal (I1
) Satisfies the oscillation condition, and the input signal (I2) to the terminal T2 satisfies the oscillation condition, in the AND logic operation oscillator 1, each of the transistors of the logical product operation oscillator 1 is Q 6 OFF → Q 7 OFF → Q. 1 ・ ON → Q 2 ・ ON → Q 3 ・ ON → Q 4 ・ OFF →
Q 5 ・ ON → Q 6 ・ ON → Q 7 ・ ON → Q 1 ・ OFF → Q
2. Off ... Oscillates in the process.

Then, the circuit element R that constitutes the logical product operation oscillator 1
Even if one of 1 to R17 and Q1 to Q7 is short-circuited or broken, the AND operation oscillator 1 does not oscillate.

Therefore, in this logical product circuit, the logical product operation oscillator 1 does not oscillate unless the level of the input signal (I1, I2) is within the window of the window comparator circuits 10, 11, and between the output terminals T6, T7 of the rectifier circuit 3. No rectified output (Vout) is generated. The rectified output (Vout) when the logical product operation oscillator 1 is oscillating is E <Vout <V.

Therefore, when the same logical product circuit is cascade-connected to the logical product circuit shown in FIG.
6 may be connected to the input terminal T1 or T2 of the logical product operation oscillator in the subsequent logical product circuit. The logic circuit in this case uses the window comparator circuits 10 and 11 as the logical product operation oscillator 1, and the power supply potential (V) of the amplifier 2 is set to be higher than the upper threshold value of the window of the window comparator circuits 10 and 11. Even if the power supply potential (V) at the terminal T5 is directly input to the rectifying / smoothing circuit 3 due to a short-circuit failure in the capacitor 30 that AC-couples the amplifier 2 and the rectifying circuit 3 because of the high level, The output (Vout) of the rectifier circuit becomes the power supply potential (V), and the window comparator circuit 10, 11 of the AND operation oscillator 1 of the next stage.
Higher than the windows. As a result, in the logic circuit in this case, the subsequent AND circuit does not oscillate, and the fail-safe operation can be achieved.

The power supply (E) of the logical product operation oscillator 1 divides the power supply potential (V) of the amplifier using, for example, a resistor and a Zener diode, and the terminal voltage of the Zener diode is used as the power supply of the logical product operation oscillator 1 (Zener diode). The terminal voltage of is used as the power source of terminals T3 and T4)
The AND circuit of FIG. 1 can be one power supply circuit of the power supply voltage V.

Then, the logical operation circuit using the logical product circuit of FIG. 1 becomes a power supply circuit of the power supply voltage V, and between the logical product circuits,
As shown in FIG. 1 and FIG. 3, the arithmetic circuit may be coupled through a rectifier circuit clamped to the ground potential and a signal may be transmitted only within the power supply frame.

EFFECTS OF THE INVENTION As described above, the present invention uses a window comparator circuit having a threshold level above and below an input signal and not oscillating due to a failure of a circuit element as an AND operation oscillator. Since the power supply potential of the amplifier for amplifying the output signal is set to a level higher than the upper limit threshold level of the window comparator circuit and the rectifier circuit is followed by the AND circuit, the oscillation start voltage of the window comparator circuit is formed. Can be within the frame of the power supply voltage, and the AND operation circuit can be configured in a fail-safe manner without using the rectification circuit as a voltage doubler rectification circuit that clamps its output to the power supply voltage.

Further, if the output level of the processing circuit provided in the preceding stage is made higher than the threshold value of the logical product operation oscillator and the output level is lowered to the threshold value by the constant voltage circuit to be the input of the logical product operation oscillator, it becomes constant. Even if the voltage circuit should fail and its output level becomes higher than the threshold value, no output is generated in the AND logical operation oscillator. Therefore, an oscillator circuit and a rectifier circuit may be provided in the previous stage as in the conventional case. Instead, there is an effect that the DC output of a general processing circuit can be input.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a logical product circuit according to the present invention. 1: Logical AND operation oscillator, 2: Amplifier, 3: Rectifier circuit, 10: Window comparator.

Claims (1)

[Claims] (A) An input signal has upper and lower threshold values, and oscillates and outputs an alternating current only when the input signal is between the upper and lower threshold values to form a circuit. A logical product operation oscillator that does not oscillate when a failure occurs in an element, and (b) a power supply potential higher than the upper limit threshold value of the logical product operation oscillator for amplifying an output signal of the logical product operation oscillator. An amplifier circuit; and (c) a rectifier circuit that clamps the output signal of the amplifier circuit to the zero potential of the power supply and rectifies the output signal, and (d) sets the upper limit threshold of the AND operation oscillator to An AND circuit that is set to a level lower than the power supply potential of the amplifier circuit.