JPS6147447B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform shaping device that converts an alternating current waveform into a square waveform.

In this type of device, a differential amplification circuit is used,
Further, a configuration in which an offset is provided so as not to respond to minute inputs has been separately proposed and filed. According to this, even if there are variations in the characteristics of the transistors used, they cancel each other out and stable waveform shaping becomes possible. Also, due to the existence of the offset, malfunctions due to noise, drift, etc. can be reliably avoided. This method has the advantage that an offset can be easily applied, and is extremely advantageous.

By the way, such a differential amplifier circuit is composed of a pair of transistors, each emitter of which is connected to a common constant current source, and each collector of which is connected to a DC power supply via a current mirror circuit. In this case, in order to make both transistors equally active, a predetermined bias is applied to the base of each transistor from the bias terminal via the bias resistor, an AC input signal is superimposed on the base of one, and the output is output from the collector of the other. It's being taken out.

However, with this configuration, a problem arises due to the fact that the current amplification factor of the transistor is a finite value.
That is, when an AC waveform input signal is applied to one base, the base current follows the change in the collector current of the other base, and the bias potential of the other base changes by the change in voltage drop across the bias resistor.
Therefore, as the current amplification factor of the transistor becomes smaller, the input signal as a differential input becomes equivalently smaller.

Conversely, when the current amplification factor becomes larger than the design value, even if a constant offset is given as described above, the offset level will become small from the perspective of the input signal, causing malfunctions due to noise, etc. Put it away.

This invention uses a differential amplification circuit for waveform shaping,
In addition, when an offset is given, it is an object of the present invention to prevent the width of the offset from decreasing due to an equivalent decrease in the input signal, and to ensure stable waveform shaping.

Before explaining the present invention, an example of use of the present invention will be explained. FIG. 1 shows a speed control device for a DC motor, and FIG. 2 shows signal waveforms appearing at each point a to f in the figure. An output signal a from a frequency generator 2 that outputs a frequency corresponding to the rotational speed of a motor 1 to be controlled (for example, a micromotor)
is applied to the waveform shaping circuit 3, where it is converted into a square wave signal b. The signal b is passed through the differentiating circuit 4,
For example, it is differentiated at its falling edge and outputs a signal c. This signal c triggers the monostable multivibrator 5, thereby producing a square wave-like signal d with a constant width. This signal d is then passed to the integrator circuit 6
is integrated and outputs an integral output e. This output e is compared with the reference voltage E _S of the reference power source 8 in the comparator circuit 7, and when the integrated output e becomes larger than the reference voltage E _S , the output f that was previously output from the motor drive circuit 9 changes. fall more.

In the above configuration, as the rotational speed of the motor 1 gradually increases, the frequency of the output signal a from the frequency generator 2 also gradually increases, and thereby the interval between the signals d of the monostable multivibrator 5 becomes shorter. I'm getting used to it. Therefore, the integrated output e from the integrating circuit 6 gradually increases, and this increases the reference voltage E.
When _S is exceeded, the output f from the motor drive circuit 8
falls, and the power supply to the motor 1 is stopped. Conversely, when the rotational speed of the motor 1 is decreasing, power supply to the motor 1 is restarted when the integral output e from the integrating circuit 6 becomes smaller than the reference voltage E _S .
As a result of the above, the motor 1 comes to rotate at a constant speed.

The waveform shaping circuit 3 of this invention is used in the waveform shaping circuit 3 having such a configuration. If a conventional waveform shaping circuit 3 having a configuration that causes malfunctions due to drift or other factors is used, the following problems will occur. That is, suppose, for example, that the rotating shaft of the motor 1 is forced to stop by applying an overload from the outside. At this time, the output signal a from the frequency generator 2 is no longer output, but if at this time a minute signal from the waveform shaping circuit 3 is input due to noise from other circuits or due to drift, the waveform will be shaped each time. Then, a signal d is output from the monostable multivibrator 5. As a result, when the integrated output e from the integrating circuit 6 exceeds the reference voltage E _S , the power supply to the motor 1 is stopped. Even if the overload is removed after such a state is reached, the motor 1 will not be able to be restarted because the power supply to the motor 1 has been stopped.

Also, while the motor 1 is rotating, the frequency generator 2
There is no compensation to always maintain a constant amplitude of the signal a from . For example, as frequency generator 2,
When using a structure in which a large number of magnets are installed at equal intervals around the periphery of a rotating disk rotated by the rotation of the motor 1, and the Hall element is excited by the magnetic flux from each magnet, When the rotating disk rotates with wobbling, the distance between the magnet and the Hall element changes, and the electromotive force of the Hall element, that is, the amplitude of the signal a, changes greatly. Therefore, the interval of the signal d from the monostable multivibrator 5 will not respond correctly to the frequency of the signal a, and the motor 1 may run out of control.

In order to prevent these malfunctions, it is possible to set an offset in the waveform shaping circuit 3 and perform waveform shaping on input signals that exceed this offset range, but if this offset is not stably set, This causes malfunctions like those mentioned earlier. In this case, if the waveform shaping circuit is constructed from a differential amplification circuit according to the present invention, a stable offset can be easily set.

An embodiment of the present invention will be described below with reference to FIG. 11 is the signal a from the frequency generator 2 in FIG.
12 and 13 are a pair of transistors, 14 is a terminal to which a bias voltage is applied, 15 and 16 are bias resistors whose resistance values are almost equal to each other, 17 is a constant current source, 18 is a power supply line, 1
9 is a diode, 20 is a transistor, which together with the diode 19 constitute a current mirror circuit,
The transistor 20 operates so that a current equal to the current flowing through the diode 19 flows between the collector and emitter of the transistor 20. Reference numeral 21 is an output terminal, and by connecting a load thereto, a voltage with an output current is generated between it and a reference potential.

In the above configuration, when no input signal is applied to the input terminal 11, the base potentials of both transistors 12 and 13 are considered to be equal to each other, so the currents I ₁ and I ₂ flowing through both transistors 12 and 13 are equal. The sum of these two currents becomes the constant current I ₀ flowing through the constant current source 17. In this state, the currents flowing through transistors 20 and 13 are equal, so
The output of the output terminal 21 is at L level. Next, when an AC waveform such as signal a is applied to the input terminal 11, and if the AC waveform crosses zero and enters the positive range, the base potential of the transistor 12 will be higher than the base potential of the transistor 13. So,
The current I ₁ becomes larger than before, and therefore the current I ₂ becomes smaller. At this time, the same current as the increased current _I1 tries to flow through the transistor 20, but only _a smaller current _I2 flows through the transistor 13 by the amount of the increased current I1. The collector potential of , that is, the output of the output terminal 21 is inverted to H level.

Conversely, if the input signal crosses zero and enters the negative range, the current flowing through the transistor 12 will be smaller than the current _I1 , and conversely the current _I2
increases. However, since the same current as the reduced current I ₁ is going to flow through the transistor 20, the output of the output terminal 21 becomes L level. As a result of the above, an output whose waveform has been shaped in accordance with the positive range of the input signal is obtained from the output terminal 21. In other words, the required waveform shaping can be performed using the differential amplification circuit.

In order to provide an offset in such a circuit, a current source 22 is connected to the collector of the transistor 13 as shown in the figure. And this current source 22
It is assumed that the limit value I ₀ ' of the current that can flow satisfies I ₀ '=KI _{0 (} however, 1>K>0) in relation to the constant current I 0 .

In this configuration, when an input signal is applied to the input terminal 11, even though the current I ₂ decreases from the moment it crosses the input signal and enters the positive range, the current from the transistor 20 continues to flow through the current source 22. flows into
It does not flow to the output terminal 21. As the input signal further increases, the difference between the currents I ₁ and I ₂ (I ₂ = I ₀ − I ₁ ) obtained by amplifying the base current that increases accordingly becomes the limit value of the current that the current source 22 can flow. When the voltage becomes larger than I ₀ ', a current flows to the output terminal 21 for the first time, and its potential becomes H level. This gives an offset to the input signal. The above relationship is illustrated in FIG. 4, where the constant current source 22 generates an offset voltage V
When _0S is set, the signal b to be waveform shaped is
It rises when the input signal a exceeds the offset voltage V _0S , and falls when it becomes smaller than the offset voltage V _0S . Since the offset voltage can be determined by setting the current capacity of the current source 22 determined by the current ratio with the constant current source 21, it is extremely stable.

By the way, if we examine the configuration shown in FIG. 3 in more detail, we will first consider the case where no input signal is applied to the input terminal 11.The potential of the base of the transistor 12 will be higher than the potential applied to the terminal 14. , the potential is lower by the voltage drop across the resistor 15, and the potential at the base of the transistor 13 is also lower by the voltage drop across the resistor 16. If the resistance values of both resistors 15 and 16 are kept the same, both base potentials are the same. Assume that an input signal is applied to the input terminal 11. As this input signal increases within the positive range, the base potential of transistor 12 becomes high and transistor 1
The current I ₁ flowing through 2 becomes larger than before. On the other hand, since the sum of currents I ₁ and I ₂ is always constant due to the constant current source 17, as current I ₁ increases, current I ₂ becomes lower than before. As a result, the base current of transistor 13 also becomes smaller than before, and the voltage drop caused by resistor 16 also becomes smaller, thereby restoring the base potential of transistor 13. Conversely, if the input signal decreases, the base potential of the transistor 13 also decreases for the same reason. In other words, this base potential will fluctuate in the same way as the input signal signal increases or decreases. Here, if the transistor 13 were an ideal transistor, the current amplification rate would be infinite, so such fluctuations would not occur, but since the current amplification rate generally has a finite value, this Such fluctuations are unavoidable, and the smaller the current amplification rate, the wider the fluctuations. Therefore, even if an input signal is applied, as shown in Fig. 5, the signal level will equivalently be in a state similar to a drop, and if the drop is large enough that the collector current of the transistor 20 does not reach the limit value I ₀ '. In this case, the output pulse will not be generated and malfunction will occur.

In order to prevent this, it is conceivable to keep the offset level sufficiently low, but if this is done, malfunctions due to noise etc. as already mentioned will occur.

Therefore, in this invention, the equivalent variation depending on the current amplification factor of the level of the input signal a is canceled out, and for this purpose, the resistor 15 is used rather than the resistor 16.
For example, reduce the resistance value of resistor 16.
It is set to about 0.8 to 0.95 times.

If this is done, the voltage drop across the resistor 16 will be greater than the voltage drop across the resistor 15 when no input signal is applied, so that the base potential of the transistor 12 will be equal to the base potential of the transistor 13 on average. Becomes higher.

That is, as shown in FIG.
Since the base potential of the offset becomes higher, the offset level V _0S appears to have shifted to the level v _0S . Therefore, even if the current amplification factor of the transistor is low and the current amplitude is equivalently small, the offset level is corrected to _V0S , so that a waveform-shaped pulse can always be obtained.

In other words, when this circuit device is configured in an integrated circuit, it is possible to set a stable offset even if there are variations in the current amplification factor of the transistors, thereby preventing malfunctions caused by minute voltages. Malfunctions such as pulse omission can be avoided.

As detailed above, according to the present invention, when shaping a waveform using a differential amplification circuit, even if the current amplification rate is finite as a transistor constituting the differential amplification circuit, Even if there are variations, the set offset can be maintained reliably, and stable waveform shaping becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of use of this invention, Fig. 2 is a waveform diagram for explaining operation, Fig. 3 is a wiring diagram showing an embodiment of this invention, and Figs. 4 to 6 are waveforms for explaining operation. It is a diagram. 11...Input terminal, 12, 13...Transistor, 14...Bias terminal, 17...Constant current source,
19...Diode, 20...Transistor, 2
1... Output terminal, 22... Current source.

Claims (1)

[Claims] 1. The emitters of a pair of transistors constituting a differential amplifier circuit are connected together to a constant current source, the collectors of both transistors are connected to a DC power supply via a current mirror circuit, and one of the transistors is connected to a constant current source. An input terminal to which an AC waveform signal to be waveform-shaped is applied is connected to the base of the transistor, an output terminal is connected to the collector of the other side, and a bias power supply terminal is connected to the base of each transistor via a bias resistor. , a current source having the ability to flow a current smaller than the current flowing through the constant current source is connected to the collector of the other transistor, and the bias resistance of the one transistor is set to be lower than the bias resistance of the other transistor. A waveform shaping device with a small resistance value.