JPH0154885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monostable multivibrator, and particularly to a transistor monostable multivibrator circuit that is most suitable for integration into an integrated circuit.

A monostable multivibrator is widely known as a typical circuit that generates a pulse with a constant pulse width in synchronization with an input trigger pulse. FIG. 1 shows an example of a conventionally used transistor monostable multivibrator. This circuit is widely known as a collector-base coupled monostable multivibrator, and the common emitter connection point of transistors 51 and 52 is grounded via a resistor 54, and a capacitor 63 is connected in parallel with this resistor 54. It is connected. The collectors of the transistors 51 and 52 are each connected to a resistor 5.
The collector of the transistor 51 is connected to the base of the transistor 52 via the capacitor 61, and the collector of the transistor 52 is connected to the power supply line 65 via the capacitor 62 and the resistor 59. 51
connected to the base of. Furthermore, capacitor 61
The connection point between and the base of the transistor 52 is the resistor 5
The connection point between the parallel connection circuit of the capacitor 62 and the resistor 59 and the base of the transistor 51 is grounded through the resistor 53. A trigger signal is applied from an input terminal 66 to the collector of the transistor 51 via a differentiator circuit including a capacitor 60 and a resistor 55 and a diode 64, and an output is taken out from an output terminal 67 connected to the collector of the transistor 52.

In such a collector-base coupled monostable multivibrator, a pulsed trigger signal is differentiated by a capacitor 60 and a resistor 55, and the negative component of the differentiated output is applied to the collector of the transistor 51, and at the same time, the pulsed trigger signal is applied to the collector of the transistor 51 via the capacitor 61. is applied to the base of , turning transistor 52 off. At this time, transistors 51 and 5
Since the transistor 2 constitutes a differential amplifier, the state in which the transistor 52 is in an off state and the transistor 51 is in an on state is maintained. However, capacitor 62 is then charged and transistor 5
When the base potential of the transistor 1 falls, the transistor 51 is turned off and the transistor 52 is turned on. Therefore, an output pulse having the pulse width during the off state of transistor 52 is produced at output terminal 67.

Such a collector-base coupled monostable multivibrator requires four capacitors, elements that cannot be integrated into an integrated circuit. Therefore, if it were integrated into an integrated circuit, it would require four external terminals in addition to the input/output terminals and power supply terminals. shall be. Furthermore, since either transistor 51 or 52 is always on, power consumption also increases. Furthermore, the pulse width of the output pulse is determined by the base voltage of transistor 51 and the threshold voltage of transistor 51. However, since the threshold voltage of the transistor 51 is greatly affected by the operating temperature, there is a drawback that the pulse width of the output pulse is greatly affected by the ambient temperature and the operating temperature. Also, resistors 53, 58, 5
Transistor 51 determined by 9 and capacitor 62
The base voltage also changes depending on the power supply voltage, so the pulse width of the output pulse has the disadvantage that it is also greatly affected by the power supply voltage.

As described above, conventional monostable multivibrators are unsuitable for integration into integrated circuits, and have the drawback that the output pulse width is greatly affected by operating conditions.

An object of the present invention is to provide a monostable device which can have a desired pulse width determined by the charging time constant obtained by connecting a resistor and a capacitor in series, and which can be configured with one terminal, which is the minimum number in integrated circuits. Our goal is to provide a multi-vibrator. Furthermore, according to the present invention, it is possible to create a configuration in which the output pulse width is not affected by the characteristics of circuit elements other than the charging time constant, which is extremely stable against power supply voltage fluctuations and ambient temperature changes, and is easy to integrate into integrated circuits. An optimal monostable multivibrator can be obtained.

According to the present invention, there is provided a series connection circuit of a resistor and a capacitor to which a power supply voltage is applied to one end and the other end is grounded, and a first transistor connected to a connection point between the resistor and the capacitor for discharging the charge of the capacitor. a switch circuit, a differential comparison circuit that compares a reference voltage and the charging voltage of the capacitor, a current supply source that supplies current to this differential comparison circuit, and a second transistor switch that cuts off this current supply source. an input terminal for receiving an input gate signal for simultaneously driving a first transistor switch circuit and a second transistor switch circuit; a third transistor switch circuit for simultaneously shutting off the first transistor switch circuit and the second transistor switch circuit;
The monostable multi-channel transistor switch circuit operates the third transistor switch circuit only for a certain period of time determined by the values of the resistance and capacitance from the time when the transistor switch circuit switches from a conductive state to a cutoff state in response to an input gate signal. Get a vibrator.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 2 is a functional block diagram for explaining the operation of the monostable multivibrator according to the present invention. In the figure, a resistor R and a capacitor C are connected in series, a power supply voltage Vcc is applied to one end of the resistor R, one end of the capacitor C is grounded, and the connection point of the resistor R and capacitor C is connected to a terminal A. has been done. Terminal A
A first transistor switch circuit 1 is connected to the input terminal 4, and when no input trigger signal is applied to the input terminal 4, the charge in the capacitor C connected to the terminal A is discharged, and the terminal A is short-circuited to approximately the ground potential. ing. Terminal A is further connected to a differential comparison circuit 5, which compares and amplifies the reference voltage V _R and the potential of terminal A, and supplies the output to the third transistor switch circuit 3. Differential comparison circuit 5
The current supply source 6 for operating the first
When no input signal is applied to the input terminal 4 connected in parallel with the transistor switch circuit, the current supply is cut off. The third transistor switch circuit 3 is connected to simultaneously cut off the first transistor switch circuit 1 and the second transistor switch circuit 2, forming a feedback loop.

As described above, when no input trigger signal is applied, the first transistor switch circuit 1 and the second transistor switch circuit 2 are operating, and the current supply source 6 is cut off, so the differential comparator circuit 5. The third transistor switch circuit 3 is in a cut-off state. Therefore, when an input trigger signal is applied to the input terminal 4 to cut off the first transistor switch circuit 1 and the second transistor switch circuit 2, charging of the discharged capacitor C starts through the resistor R, and the terminal A Potential is time constant CR
(where C and R are the respective values of capacitance C and resistance R). On the other hand, the current supply source 6 starts operating and supplies an operating current to the differential comparator circuit 5, so that the differential comparator circuit 5 can compare and amplify the potential of the terminal A and the reference voltage _VR . Terminal A
An output current for driving the third transistor switch circuit 3 is supplied to the output of the differential comparator circuit 5 during a period until the charging potential of the differential comparator circuit 5 reaches the reference voltage _VR .
When the third transistor switch circuit 3 operates, the first transistor switch circuit 1
Since the first transistor switch circuit 1 and the second transistor switch circuit 2 are cut off, the first transistor switch circuit 1 and the second transistor switch circuit 2 are cut off at the same time as the input trigger signal is applied.
The transistor switch circuit 2 continues to be kept in the cut-off state even if no input trigger signal is applied. When the charging potential of terminal A rises and reaches the reference voltage _VR , the output of the differential comparator circuit 5 is inverted and the third
The first transistor switch circuit 1 and the second transistor switch circuit 3 are switched to cutoff.
The transistor switch circuit 2 returns to its original operating state.

As described above, after the input trigger signal is applied, the third transistor switch circuit 3 operates only for a certain period determined by the resistor R, capacitor C, power supply voltage Vcc, and reference voltage _VR , and supplies an output pulse to the output terminal 6. Therefore, this is nothing but the operation of a monostable multivibrator.

FIG. 3 is a circuit connection diagram showing a specific embodiment of the monostable multivibrator according to the present invention, and FIG. 4 is a voltage waveform diagram of each part for explaining the operation of FIG. 3.

In FIG. 3, a transistor 12 to which a power supply voltage Vcc is applied via an emitter resistor 11 is normally forward biased as a grounded emitter circuit and supplies a constant collector current. transistor 12
The collector of is connected via a diode 13 to the base of a transistor 14 whose emitter is grounded.
Furthermore, it is connected via a resistor 15 to the base of a transistor 16 whose emitter is grounded. Transistor 14 corresponds to the first transistor switch circuit in FIG. 2, and its collector is connected to terminal A. A portion of the collector current of the transistor 12 flows through the resistor 17, but it is supplied as a base current to the transistors 14 and 16, keeping them in a conductive state. Similarly to FIG. 2, a resistor R and a capacitor C are connected to the terminal A, and the electric charge of the capacitor C is discharged by conduction of the transistor 14, so that the terminal A is held at approximately the ground potential. Transistors 17 and 18, whose emitters are commonly connected, constitute a differential comparison circuit, and transistor 1
The potential of terminal A is at the base of transistor 1.
A reference voltage V _R obtained by dividing the power supply voltage Vcc by resistors 19 and 20 is applied to the base of 8. A current supply source for supplying the emitter currents of the transistors 17 and 18 is composed of a transistor 24 whose base is connected to a bias voltage source 22 via a resistor 21 and whose emitter is grounded via a resistor 23.
However, since the collector of the transistor 16 is connected to the base of the transistor 24 and the transistor 16 is in a conductive state, the transistor 24 and the transistors 17 and 18 are cut off and no current flows. Therefore, the current mirror transistor 25 connected to the collector of the transistor 18 is also cut off, and since no current is supplied to the resistors 26 and 27 connected to the collector, the transistor 28 corresponding to the third transistor switch circuit is also cut off. It's getting old.

Now, when the base of transistor 12 is momentarily reverse biased by the input trigger signal, transistors 14 and 16 are no longer supplied with base current and both switch off. and capacity C
Supply of charging current from the power supply voltage Vcc through the resistor R is started. At the same time, the transistor 24 operates as a current supply source, and the transistor 18 of the differential comparator circuit whose base is biased with the reference voltage V _R becomes conductive, and the current mirror transistor 2
5. By operating the transistor 28 and lowering the collector potential of the transistor 12, the transistors 14 and 16 are cut off and the transistors 24 and 1 are cut off regardless of the presence or absence of a subsequent input trigger signal.
8, 25, and 28 are maintained in a conductive state. A reference voltage V _R is applied to the base of the transistor 18, and when the charging potential of the terminal A reaches the reference voltage V _R , the differential transistors 17 and 18 are switched, and the transistor 18, the current mirror transistor 25, and the transistor 28 is placed in a cut-off state. If the next input trigger signal is not applied at this time, the original state is restored and the transistors 14 and 1
6 is conductive, transistors 24, 17, 18, 2
8. The current mirror transistor 25 is cut off.

In FIG. 4, when the input trigger signal applied to the base of the transistor 12 is shown by a waveform 31, the collector potential of the transistor 12 decreases in synchronization with the rise of the waveform 31, and even after the transistor 12 returns to the conductive state, the collector potential of the transistor 12 decreases. This is represented by a waveform 32 that maintains a low potential for a certain period of time due to the conduction of 28. A waveform 33 shows a change in the potential of the terminal A. Charging of the capacitor C starts at the same time as the waveform 31 rises, and is discharged by the transistor 14 when the reference voltage V _R is reached. The waveform 34 is an output pulse waveform appearing at the output terminal 6 connected to the collector of the current mirror transistor 25, and the pulse width is determined as follows.

If the charging time to reach the reference voltage V _R is T, then V _R = {1-exp (-T/CR)}Vcc T = -CRln (1-V _R /Vcc) ...(1) The pulse width is , is equal to this charging time T, as shown in FIG. Here, when the reference voltage V _R is given as a voltage proportional to the power supply voltage Vcc by resistor division as shown in Figure 3, the pulse width T' is V _R = KVcc (K
is the voltage division ratio by resistors 19 and 20, and 0<K<
Substituting 1) into equation (1), T'=-CRln(1-K)......(2) is obtained. From equation (2), the pulse width is determined by the values of the resistor R and capacitor C, and the resistors 19 and 20 that provide the reference voltage V _R.
Since it is determined by the division ratio K, it can be seen that it is not affected by fluctuations in the power supply voltage Vcc or temperature changes in V _BE of the transistor, and can be obtained very stably.

In FIG. 3, the potential at the time of discharge of terminal A is determined by the collector-emitter saturation voltage of transistor 14, and although it is not strictly the ground potential, the saturation resistance of transistor 14 is selected low, and resistor R
By setting the value of V to a large value to reduce the collector current, it is possible to make the value sufficiently negligible with respect to the reference voltage _VR . Furthermore, the discharge time of the capacitor C is determined by the collector current of the transistor 14, but is unrelated to the desired pulse width. Since transistor 17 is in a cut-off state during the charging period of capacitor C, transistor 1
7 base current has no effect. Furthermore, according to the circuit shown in Fig. 3, if the input trigger signal arrives at a sufficiently long period or very few times compared to the pulse width, many of the transistors in the circuit remain cut off. , it is possible to reduce power consumption compared to conventional circuits.

The present invention has been described above with reference to one embodiment of the present invention, but it is clear that the same operation can be achieved even if the NPN transistor and the PNP transistor are replaced, and the present invention does not extend to the entire scope of the claims. be.

[Brief explanation of drawings]

Fig. 1 is a circuit connection diagram showing a conventional example of a monostable multivibrator, Fig. 2 is a functional block diagram for explaining the operation of the monostable multivibrator according to the present invention, and Fig. 3 is a monostable multivibrator according to the present invention. FIG. 4 is a circuit connection diagram showing a specific embodiment of the present invention, and FIG. 4 is a voltage waveform diagram of each part for explaining the operation of FIG. 3. 1, 2, 3...transistor switch circuit, 4
...Input terminal, 5...Differential comparison circuit, 6...Output terminal, R...Resistance (resistance value), C...Capacitance (capacitance value), Vcc...Power supply voltage, V _R ...Reference voltage, A...
...Terminal, 11, 15, 17, 19, 20, 21,
23, 26, 27...Resistance, 12, 14, 16,
17, 18, 24, 25, 28...transistor, 13...diode, 31, 32, 33, 3
4... Voltage waveforms of each part.

Claims (1)

[Claims] 1 A series connection circuit of a resistor and a capacitor provided between a first and a second power supply terminal, a first transistor switch circuit connected to a connection point of these resistors and a capacitor, and discharging the capacitor when in a conductive state; a resistive voltage divider circuit that is provided between the first and second power supply terminals and generates a divided voltage of the power supply voltage between these terminals as a reference voltage; and a differential comparison circuit that compares the charging voltage of the capacitor with the reference voltage. , a current supply source that supplies an operating current to the differential comparison circuit to cause the differential comparison circuit to perform a comparison operation; a second transistor switch circuit that cuts off the current supply source when in a conductive state; means for responsively switching both the first and second transistor switch circuits from a conductive state to a disconnected state; and a point in time in response to an output of the differential comparator circuit that the charging voltage of the capacitor reaches the reference voltage. and a third transistor switch circuit that holds the first and second transistor switch circuits in a cut-off state until then.