JPS59165516A - Unstable multivibrator - Google Patents

Abstract

PURPOSE:To prevent an error due to an antiphase current flowing through the capacity between terminals of a constant current source by setting the potential of the output terminal of the constant current source which is not connected to the input terminal of an amplifier at a level near the threshold level of the amplifier. CONSTITUTION:The voltage of a positive voltage source terminal 4 is divided by resistances 12-14, and the terminals of switch elements 10 and 11 which are not connected to constant current sources 6 and 7 are connected to the juncture of the voltage dividing resistances. The voltage dividing ratios of resistances 12-14 are set so that the potential at the juncture of each resistance is set at a level near the threshold level of an amplifier 1. Thus the instantaneous change of potential is greatly reduced when the switch elements are changed over. This can reduce the effect of the inter-terminal capacity of the sources 6 and 7.

Description

[Detailed Description of the Invention] In an astable multivibrator that eliminates the influence of stray capacitance by supplying a constant current to the resistor, there is a method that eliminates errors caused by the capacitance between the terminals of the positive and negative constant current sources. Regarding stable multivibrator.

<Description of the Prior Art> The applicant previously disclosed in Application No. 57-98740 "In an astable multivibrator J, a capacitive element is provided in the positive feedback loop of the mi increaser, and a positive constant current source and a negative constant current source are alternately switched. The present invention provides an astable multivibrator that is unaffected by stray capacitance and is configured to supply a constant current to the capacitive element.

This circuit will first be explained based on FIG.

In Figure 1, 1 is an amplifier, 2 is a capacitor for determining the oscillation frequency, 3 is a stray capacitance, 4 is a positive voltage source terminal,
5 is a negative voltage source terminal, 6 is a positive constant current source, and 7 is a negative constant current source. The 8, 9, 10, 11 switch element 11 is connected between the positive voltage source terminal 4 and the negative constant DC source 7. The common connection point of the switching elements 8.9 is connected to the hexagonal terminal of the amplifier l. These switching elements are controlled by the output of amplifier 1. That is, the output of amplifier 1 is rHJ
When , switch elements 9 and 10 are conductive, and switch elements 8 and 11 are non-conductive. Further, when the output of the amplifier 1 is "L", the control is performed in the opposite manner to the above.

Next, the operation will be explained. The output of amplifier 1 increases from zero to +ll1
When K changes, the potential t at the input terminal of amplifier 1, that is, point A
A increases only to that threshold level. 0. Os is the capacitance of capacitor 2 and stray capacitance 3, respectively. At this time, the switch cable 9 becomes conductive,
Since point A is connected to a negative constant current source, the potential at point A falls at a constant rate, and when it falls below the threshold level of amplifier 1, its output is inverted. This time, the potential at point A drops by the above tk. Further, since the switch element 8 is conductive and the point A is connected to the positive constant current source, its potential increases at a constant rate, and when it reaches the threshold level, the output of the amplifier 1 is inverted again and returns to the original value.

Self-oscillation is performed by repeating these operations. If the time to return now is tl, and the current of the negative constant current source 7 is 11, then tA・(C+0a)=il・tl...
...(2) holds true. Substituting this into the formula +11 above, t1=0・E/11...
・・・・・・・・・・・・・・・・・・(3) That is, the oscillation frequency no longer depends on the stray capacitance CaK. The constant current source 6.7 is connected to the voltage terminal 5.4 by means of a switching element 10.11 when its output terminal is not connected to point A. Therefore, the constant current source always outputs current.

In this way, the astable multi-pipe lake shown in Figure 1 is
Since its oscillation frequency does not depend on stray capacitance, the amplifier 1
When the output E of the constant current source and the output current 11 of the constant current source are held constant, the oscillation frequency is exactly proportional to the capacitance of the capacitor 2. Furthermore, since the constant current source is constantly outputting a current due to the switching element 1011, the output current does not change even when the switching element is switched, which has the effect of further stabilizing the oscillation frequency.

However, this conventional example has the following drawbacks. FIG. 2 shows the potential of the output terminal of the positive constant current source 6 when the high level output of the amplifier 1 is set to F, its threshold level potential is 0, 5 Fi , and the potential of the negative voltage terminal 5 is set to zero. When the switch element 8 is turned on and the switch element 10 is turned off at time t1, the potential at the output terminal of the positive constant current source 6 instantly changes from zero to (0,51-LA).
(/-A is the value shown in the formula +11 above) K changes. This potential rises at a constant rate, and when it reaches the threshold level at time t2, the switching element 8 is disabled.
becomes conductive and momentarily drops to zero potential. That is, time t
1. At t2, the potential changes significantly instantaneously.

The potential of the output terminal of the negative constant current source 7 changes similarly.

Therefore, a negative phase current flows through the capacitance between the terminals of the positive and negative constant current sources 6.7, and the oscillation frequency changes. If the capacitance between the terminals of the positive and negative constant current sources is Ca, and the threshold level of the amplifier 1 is 0.5E, then the above formula 5-(1) f2) must be replaced with the following formula (41 (51).

The second term in equation (4) represents the influence of negative sequence current.

tA・(0+08+CG)-11・tl・・・・・・・
(5) Therefore, the equation representing the oscillation period corresponding to the above equation (3) is K as follows.

t1=(c-0,5CG)・E/11・・・・・・・・・
(6) That is, the oscillation frequency depends not only on the capacitance of the capacitor 2, but also on the constant current sources 6 and 7.
The inter-terminal capacitance OGK of is also dependent on K. CG varies depending on the element and also changes due to changes in the surrounding environment, which causes the oscillation frequency to become unstable.

<Summary of the Invention> The object of the present invention is to fix the potential of the output terminal of a constant current source, which is not connected to the input terminal of an amplifier, near the threshold level of the amplifier, thereby reducing the potential flowing through the capacitance between the terminals of the constant current source. It is an object of the present invention to provide an astable multivibrator that can prevent errors caused by negative sequence current.

<First Embodiment> FIG. 3 shows a first embodiment of the present invention. 1 is an amplifier,
2 is a capacitor, 3 is a stray capacitance, 4 is a positive voltage source terminal, 6
．． 7 are positive and negative constant current sources, 8G, and 10.11 are switching elements, which function in the same way as the conventional example shown in FIG. 1, so their explanation will be omitted. In this embodiment, no negative voltage source terminal is provided, and one end of the negative current source 7 is connected to a common potential point. In this embodiment, the voltage at the positive voltage source terminal 4 is divided by a resistor 12°13.14, and the switching element 10.11
The terminal on the side that is not connected to the constant current source is connected to the connection point of these voltage dividing resistors. The voltage division ratio of the resistors 12.13.degree. 14 is set so that the potential at the connection point of each resistor, that is, the other end of the switching element 10.11, is near the 2-reshold level of the amplifier l. FIG. 4 shows the potential of the output terminal of the positive constant current source 6 corresponding to FIG. 2. As can be seen from this figure, the instantaneous change in potential when the switch element is switched is on the order of El, which is much smaller than in FIG. 2. Therefore, the above equation (4) becomes the following equation (7), and the above equation (6) representing the oscillation period becomes the equation (8).

- Ma - 0 0G c+cs+cG o+cs+cG 1 t1=(0-1・CG)・F! /il・・・・・・・・・
・・・・・・・・・・・・・・・+81, that is, by adjusting the voltage dividing ratio of resistors 12, 13, and 14, and decreasing 1cLE1 so that the divided voltage is close to the threshold, the constant The influence of the inter-terminal capacitance CO of the current source 67 can be reduced. In this example, resistor 13
The reason why the voltage applied to the switch element 10 and the switch element 10 by 11K is made different is to reduce the instantaneous change in potential at time t1'.

<Second Embodiment> FIG. 5 shows a second embodiment. In this embodiment, a diode 1516 is connected in place of the switch element 10.11. The diode 15 has its anode connected to the output terminal of the positive constant power supply 6, and its cathode connected to a voltage dividing circuit consisting of resistors 17 and 18. Further, the diode 16 has its cathode connected to the output terminal of the negative constant current source 7, and its anode connected to a voltage dividing circuit consisting of resistors 17 and 18. As shown in FIG. 4, while the switching element 8 is conducting (between tl and t2 in FIG. 4), the potential of the output terminal of the positive constant current source 6 is lower than the threshold level of the amplifier 1, so the resistance 17 and 18
To set the output voltage of the voltage divider circuit equal to the threshold level, the voltage divider circuit and the output shield of the positive constant current source 6 are switched by a diode 15. Further, when the switch element 8 becomes non-conductive, the output current of the positive constant current source 6 flows through the diode 15. Also, diode 16
works in the same way. That is, the diode 1516 operates in the same way as the switch element 1011 of the first embodiment shown in FIG.

<Third Example> A third example is shown in FIG. In this example, diodes 19, 20, 21, 22 are used as switching elements. If the output of the amplifier 1 now becomes rHJ, the output of the inverter 24 becomes "L"K. Therefore, the positive constant current source 6
The output current flows into the inverter 24 through the diode 19.

Also capacitor 2. The charges accumulated in the floating capacitor 1it31c flow into the negative constant current source 7 through the diode 21. When the output of the amplifier l becomes rLJ, current flows from the inverter 24 into the negative constant current source 7, and the positive constant current source 6
From capacitor 2. Charge is supplied to the floating capacitance 3. Similarly, the diodes 19-22 operate in the same manner as the switching elements 8-11 of the first embodiment. In this embodiment, a resistor 23 is further provided at the output of the inverter 24.

Due to the voltage drop across this resistor, the potential of the output terminals of the constant current sources 6 and 7 when they are not connected to the input terminal of the amplifier 10 is set near the threshold level of the amplifier. The same effects as in the second embodiment can be obtained. The output of the inverter 24 is connected to the resistor 2 as shown in Figure 7.
The voltage may be divided by 5.26 and connected to a diode circuit.

<Application example> An example of obtaining an output proportional to the ratio of the sum and difference of two capacitances using the astable multivibrator of the first embodiment shown in Fig. 3 is shown in Fig. 8, which corresponds to Fig. 3. are shown with the same symbols. The oscillation output from the amplifier 1 is manually counted by the n-bit counter 37, and the rubit-th output terminal 38 of the 10-counter 37 is directly connected to the NAND gate 2 through the inverter 39 or without going through it.
7.28. The count value of counter 37 is 2'1
Before , the terminal 38 is at a low level and the gate 27 is opened,
The oscillation output of amplifier 1 is connected to NAND through inverter 36.
The signal is supplied to the gate 27. Each output of the NARD gate 27.28 is connected to a capacitor 311.31 and a positive electrode 32a, 32b. Further, a common electrode 33 is provided opposite the electrodes 32a and 32b, and is connected to the non-inverting input terminal of the amplifier 1 and to the connection point of the switch cables 8 and 9.

The common electrode 33 is moved by the physical quantity to be measured, so that the capacitances 31a, 32b are in opposite directions! be placed in a position. The oscillation signal at the non-inverting input terminal of the amplifier 1 is converted into DC by the low-pass F-wave generator 34, and the oscillation signal at the non-inverting input terminal
11 voltage and is supplied to the inverting input terminal of the amplifier 1 as a threshold voltage. When the HAND gate 27 is open, the amplifier IK capacitor 31a is connected to form a positive feedback loop, and therefore oscillates at a frequency fl that is inversely proportional to this capacitance. When the count value of the counter 37 reaches 2rL-1, the n-bit terminal 38 becomes [JK, NAND
The gate 28 is opened, the capacitor 31b is connected to the positive feedback loop of the amplifier 1, and oscillation with a frequency f2 that is inversely proportional to the capacitor iK occurs.

When the count value of the counter 37 reaches 2rLK, the output of the terminal 38 becomes "L", and the above steps are repeated. Therefore, the output of the terminal 38 of the counter 37 changes the frequency f1 to 2rL-
During the period when one piece is counted, “L” 2 frequency f2 is 2n-1
The period during which pieces are being counted becomes "■", and this is repeated. This output becomes an analog value proportional to the smoothing circuit. N
The output of the AND gate 2728 is also supplied to the WAND gate 29, and the output side of the NAND gate 29 has a capacity of 31 m,
31bK is connected to the non-inverting input terminal of the amplifier 1 through a parallel stray capacitance compensation capacitor element 30 that removes the influence of stray capacitances added in parallel.

<Effects of the Invention> As described above, in this invention, the potential of the output terminal of the constant current source on the side not connected to the input terminal of the amplifier 1 is maintained near the threshold level of the amplifier. This minimizes sudden changes in the potential of the output terminal. Therefore, the magnitude of the error current flowing through the capacitance between the terminals of the constant current source is reduced, and the output frequency is precisely proportional to the capacitance of the capacitor. Such an astable multivibrator can be used as a measuring device for measuring physical quantities by converting a single flow cap into a volume and measuring the volume, as shown in Application μ in Figure 8. Particularly suitable.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram showing a conventional astable multivibrator, Fig. 2 is a diagram showing the potential of the output terminal of the positive constant current source in the conventional example of Fig. 1, and Fig. 3 is a diagram of the astable multivibrator of the present invention. 4 is a diagram showing the potential of the output terminal of the positive constant current source in the embodiment shown in FIG. 3, and FIG. 5 is a connection diagram showing the second embodiment of the astable multivibrator of the present invention. 6 is a connection diagram showing the third embodiment of the astable multiper 13-ibrator of the present invention, and FIG.
Another embodiment of the voltage dropping means shown in the embodiment shown in FIG. 8 is a connection diagram of a device that uses the astable multivibrator of the present invention and obtains an output proportional to the ratio of the sum and difference of two capacitances. 1: Amplifier, 2: Capacitor, 3: Stray capacitance. 6: Fixed constant current source, 7: Negative constant current source, &9,10°11=
Switch element, 24, 36. :Inverter. Patent applicant Hokushin Electric Manufacturing Co., Ltd. Representative Masahiro Shimizu 14- Figure 2 Figure 4 □0

Claims (1)

[Claims] It has an amplifier, a capacitive element connected to the amplifier to form a positive feedback loop, a positive constant current source, and a negative constant current source, and the positive constant current source and the negative constant current source are connected to each other according to the output of the amplifier. Current is alternately supplied from the source to the capacitive element, and the potential of the output terminal of the constant current source that is not supplying current to the capacitive element among the positive constant current source and the negative constant current source is set approximately to that of the amplifier. An astable multivibrator characterized by maintaining the vibration at a threshold level.