JPH0225291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform shaping circuit including a transistorized bistable multivibrator.

Conventionally, bistable multivibrators have been used in frequency dividing circuits and the like, and among these, there are many saturated types that use a fixed bias, which have a simple circuit configuration and are highly stable against changes in external loads. A waveform shaping circuit includes this bistable multivibrator and a trigger circuit that drives the bistable multivibrator.

FIG. 1 shows an example of a conventional waveform shaping circuit,
In the figure, first and second transistors 10 and 11 and resistors 6, 7, 8 and 9 constitute a bistable multivibrator, terminals 1 and 2 are power supply terminals, and terminal 2 is normally grounded. Terminals 4 and 5 are output terminals. A trigger circuit is configured by third and fourth transistors 12 and 13 and resistors 14 and 15, and is for driving transistors 10 and 11.
Terminal 3 is a trigger signal input application terminal. The emitters of transistors 10 and 11 are grounded, and the collector of transistor 10 is connected to power supply terminal 1 through resistor 6 and also to output terminal 4. The collector of the transistor 11 is connected to the power supply terminal 1 through the resistor 7 and also to the output terminal 5. transistor 10
The bases of and 11 are connected through resistors 8 and 9 to the collectors of transistors 11 and 10. The emitters of transistors 12 and 13 are connected to the bases of transistors 11 and 10, the bases of transistors 12 and 13 are connected to the collectors of transistors 13 and 12, and the collectors of transistors 12 and 13 are connected to the input through resistors 14 and 15. Connected to terminal 3. In the above circuit configuration, it is preferable that transistors 10 and 11, 12 and 13 have the same characteristics, and resistors 6 and 7, 8 and 9, and 14 and 15 have substantially the same resistance values.

The operation of such a waveform shaping circuit is as follows. When the first transistor 10 is on,
The saturation voltage of the transistor 10 is applied to the base of the second transistor 11 through the resistor 8, but since the forward voltage between the base and emitter of the transistor is sufficiently large compared to the saturation voltage, the transistor 11 is turned off. So, transistor 10
The current determined by resistors 7 and 9 continues to flow through the base of , and is in a stable state. Now input terminal 3
If a positive trigger signal is applied to
The current determined by the resistor 15 flows through the base, and the sum of the currents flows into the base of the transistor 11 through the emitter, so that the transistor 11 is forcibly turned on. At this time, the collector potential of the transistor 11 decreases, and this voltage is transmitted to the base of the transistor 10 and acts to reduce the collector current of the transistor 10. This current change is detected by the resistor 6 and increases the base current of the transistor 11. Eventually, the transistor 10 is off and the transistor 11 is on, resulting in a stable state. At this time, transistor 13 is in an off state.

The above operation will be explained in the case where the trigger signal shown in FIG. 2 is applied.

The trigger signal 20 shown in FIG. 2 has a repetition frequency of 1/T, and this value is sufficiently smaller than the resolution frequency m at which the operation of the bistable multivibrator becomes unstable at frequencies above which the operation of the bistable multivibrator becomes unstable. This is a signal where the time is t _H , the time of the low level period near the ground potential is t _L , and the amplitude is represented by A. The signal state at output terminal 4 is represented as output signal 24, with amplitude B and repetition frequency 1/2T. That is, while the pulse signal 20 is at a low level, the transistor 10 is turned on and the transistor 11 is turned on.
Assuming that the transistor 12 is turned on at the moment when the pulse signal increases to a high level, the transistor 11 is turned on and the transistor 10 is turned off. 12 is on, and the instant the transistor 12 decreases to low level, it turns off, but one stable state of the bistable multivibrator continues.

The next high-level pulse signal 20 turns on the transistor 13, and returns to the original stable state through an operation completely symmetrical to that described above. The on/off state of the transistor 10 (or 11) is alternated every period T, and a square wave output signal 24 with a repetition frequency of 1/2T is output from the terminals 4 and 5. Further, after the transistor 12 (or 13) is in the on state for a certain period (t _H1 ), it is in the cut-off state for the next (t _L1 +t _H2 +t _L2 ) period.

In such a waveform shaping circuit, the low level period t _L
When a short pulse signal 20 with a large duty cycle t _H /T is applied, the transistor 12 (or 13) which is on during the high level period t _H becomes low level even when the pulse signal 20 decreases. Since the transistor 12 (or 13) is in the on state, the transistor 12 (or 13) continues to be in the on state even at the time of the next high-level pulse signal, and the bistable multivibrator does not transition. This is because the transistor 12 (or 13), which is in a saturated state during the high level period _tH , remains saturated for the accumulation time during the low level period when there is no drive signal, and then turns off. For pulse signals with a shorter low level period _tL , transistor 12 (or 13) is always in a saturated state, and transistors 10 and 1 forming a bistable multivibrator
Since only the transistor 11 (or 10) on one side of the bistable multivibrator is driven, the bistable multivibrator maintains one stable state.

The storage time of a transistor is determined by the structural conditions of the element, characteristics (eg, epitaxial layer thickness, etc.) (eg, grounded emitter forward current amplification factor _hFE , etc.), circuit conditions, etc. Figure 3 is a diagram showing the stable operating region of a bistable multivibrator when the horizontal axis is the low level period _tL of the pulse signal and the vertical axis is the amplitude of the pulse signal. This is the stable operating area of the circuit. As shown by region A in FIG. 3, even in the same stable operation region, the amplitude range of the pulse signal becomes narrower where the low level period t _L of the pulse signal is small. This is because when the amplitude is smaller than that in region A, there is insufficient drive current to reverse the stable state of the bistable multivibrator, and when the amplitude is larger, the accumulation time of the transistor 12 (or 13) described above is pulsed. Transistor 12 (or 13) is always active because it is longer than the low level period _tL of the signal.
is in a saturated state and the bistable multivibrator does not reverse.

As described above, the conventional waveform shaping circuit that includes a bistable multivibrator and a trigger circuit has the disadvantage that when the duty cycle of the pulse signal becomes large, the transition of the bistable multivibrator is not performed and the frequency dividing function is lost. was. Furthermore, even if the duty cycle of the pulse signal becomes a little small, the bistable multivibrator will not shift in response to fluctuations in the amplitude of the pulse signal, making it very difficult to set the amplitude of the pulse signal.

In view of the above-mentioned drawbacks, the present invention increases the duty cycle of the pulse signal with a simple circuit configuration, and furthermore, the transition of the bistable multivibrator is performed even in response to fluctuations in the amplitude of the pulse signal, and the present invention has a frequency dividing function. It is also an object of the present invention to provide a waveform shaping circuit that facilitates setting of the amplitude of a pulse signal.

According to the present invention, in the waveform shaping circuit configured with a bistable multivibrator including first and second transistors and a trigger circuit including third and fourth transistors, the third transistor has its emitter The fourth transistor has its emitter connected to the base of the first transistor and its base connected to the collector of the third transistor. The bases are connected, and the collectors of the third and fourth transistors are connected to one end of the first and second resistors, respectively, and the other end common connection point of these first and second resistors is connected to the trigger. A waveform shaping circuit characterized in that a third resistor is connected between the input terminal and the input terminal is obtained.

Since the third or fourth transistors 12 and 13 of the trigger circuit in the conventional waveform shaping circuit described above remain saturated, the bistable multivibrator does not transition and loses its frequency dividing function. The accumulation time when 12 and 13 are saturated is the low level period t _L of the pulse signal 20
This is due to the fact that the transistors 12, 13 are
This can be solved by reducing the accumulation time so that it does not become saturated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A waveform shaping circuit according to the present invention will be described below based on embodiments with reference to the drawings.

An embodiment of the waveform shaping circuit of the present invention will be described in the fourth embodiment.
As shown in the figure, a conventional waveform shaping circuit (see Figure 1)
The same parts are given the same reference numerals, and the difference is that the connection point between the first and second resistors 14 and 15 is connected to the input terminal 3 through the fourth resistor 17. In the embodiment of FIG. 5, the operation of the trigger circuit is such that if the transistor 12 is turned on when a positive pulse signal is applied, its collector current and base current are transferred from the input terminal 3 to the resistor 17.
After passing through the resistors 14 and 15, the collector current and base current are supplied from the input terminal 3 to the resistors 15 and 14 after passing through the resistors 17 when the transistor 13 is turned on.
It will be supplied through. Therefore, the voltage at the connection point between resistors 14 and 15 when a positive pulse signal is applied is determined by resistor 17, and its value is higher than the base voltage of transistor 12 (or 13). resistor 14 and 1 by the voltage determined by 14
The voltage will be lower than the voltage at the connection point 5. That is, V _BE12(13) >
By appropriately setting resistors 14, 15, and 17 so that V _CE12(13) > V _sat12(13), transistor 12 (or 13) will not saturate even if it is turned on, so the transistor 12 (or 13) accumulation time can be extremely reduced, and a sufficiently stable waveform shaping circuit can be obtained even for a large amplitude pulse signal with a large duty cycle.

In the above explanation, the first, second, third, and fourth transistors were described using NPN transistors, but the present invention is effective and the same effects can be obtained even when PNP transistors are used as these transistors. Needless to say, it can be done.

As described above, according to the present invention, it is possible to perform stable circuit operation even in the case of a pulse signal having a large duty cycle with a very simple configuration without impairing the function of a conventional waveform shaping circuit.

In addition, since the waveform shaping circuit according to the present invention can obtain stable operation even when a pulse signal has a large amplitude, it is stable even against fluctuations in amplitude caused by power supply voltage, ambient temperature, variations in elements, etc., so the waveform shaping circuit It also becomes easier to set up the elements that make up the .

Further, the waveform shaping circuit according to the present invention is effective when integrated into an integrated circuit. In other words, the capacitance of a capacitor that can be obtained in an integrated circuit is approximately several tens _{of PF} at most, and it can be constructed with only transistors and resistors that do not include this capacitor, and transistors or resistors placed adjacent to each other on the same semiconductor integrated circuit board are This is because a product with uniform characteristics can be obtained.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional waveform shaping circuit.
FIG. 2 is a diagram of the amplitude of the trigger pulse signal and the output signal with respect to time, and FIG. 3 is a diagram showing the stable operating region with the amplitude of the pulse signal with respect to time (low level period of the pulse signal) to explain the effects of the present invention. FIG. 4 is a circuit diagram showing an embodiment of the waveform shaping circuit according to the present invention. 1, 2...Power terminal, 3...Input terminal, 4,5
...Output terminal, 6, 7, 8, 9, 14, 15, 1
7...Resistor, 10,11,12,13...Transistor.

Claims (1)

[Claims] 1 A bistable multivibrator having a first and a second transistor, the base and collector of the first transistor being coupled to the collector and base of the second transistor, and a third and fourth transistor. , a trigger circuit having first and second resistors and a trigger input terminal, the trigger circuit triggering the bistable multivibrator in response to a trigger signal applied to the trigger input terminal; A base and a collector are coupled to the collector and base of the fourth transistor, respectively, and a collector-emitter conductive path of the third transistor is provided between one end of the first resistor and the base of the first transistor. a collector-emitter conductive path of the fourth transistor is provided between one end of the second resistor and the second transistor and the base, and the other ends of the first and second resistors are commonly connected. In the waveform shaping circuit, a third resistor for preventing saturation of the third and fourth transistors is provided between a common connection point of the other ends of the first and second resistors and the trigger input terminal. A waveform shaping circuit characterized in that: