JPH0481014A - Time constant circuit - Google Patents

Abstract

PURPOSE:To obtain an equivalently large value with circuit configuration by connecting one end of a capacitor to the input terminal of a signal polarity inversion amplifier and connecting the other end to the output terminal of this amplifier. CONSTITUTION:One end of a capacitor 7 is connected to the input terminal of a signal polarity inversion amplifier 8, and the other end of the capacitor 7 is connected to the output terminal of the amplifier 8. Namely, since the change of a potential at the input terminal of the amplifier 8 is inverse to the change of a potential at the output terminal of the amplifier 8 on the output side of a resistor 4, for capacity 6 of the time constant circuit, it is equal to a capacity value (C.G) which is gain (G) times of the amplifier 8 in respect to the capacity value (C) of the capacitor 7 as a whole. Therefore, when the resistance value of the resistor 4 is defined as R, the time constant of this circuit is shown by (R.C.G). Accordingly, when an area constituting the amplifier 8 on a substrate or the like is smaller than an area forming the large capacity (C.G), the area on the substrate is saved. Thus, without specially enlarging the resistor 4 and the capacitor 7 themselves, the equivalently large value can be obtained by the circuit configuration.

Description

[Detailed Description of the Invention] [Summary] Regarding a circuit that can obtain a simple time constant circuit with a large value, when a large value can be obtained isometrically by the circuit configuration without making the resistive element or capacitive element themselves particularly large. For the purpose of providing a constant circuit, the other end of the resistive element whose one end is connected to the first input terminal is connected to one end of the capacitive element, and the other end of the capacitive element is connected to the input terminal of @2, and a time constant circuit in which one end of the capacitive element is an output terminal,
One end of the capacitive element is connected to the input terminal of a signal polarity inversion amplifier, and the other end of the capacitive element is connected to the output terminal of the amplifier.

[Industrial application field]

The present invention relates to a circuit that can provide a simple time constant circuit with a large value.

Conventionally, the characteristics of time constant circuits used in signal differentiating circuits, integrating circuits, etc. are determined by the "time constant" determined by the product of resistance and capacitance. When used as an integrator circuit, when a large time constant was required, it was necessary to make the resistor and capacitor elements extremely large.Due to space constraints, this purpose could not be fully achieved. There was a request to develop a technique to obtain an equivalently large time constant by changing the circuit configuration, such as in a field where there is no such thing.

[Conventional technology]

FIG. 4 is a diagram showing a conventional time constant circuit. In FIG. 4, ■ indicates a signal input terminal, 2 indicates a signal output terminal, 3 indicates a ground terminal, 4 indicates a resistive element, and 5 indicates a capacitive element.

The resistance value of the resistor element 4 is R1, the capacitance value of the capacitor element 5 is C, and the output signal v generated between the output terminal 2 and the ground terminal 3
, =v, (1-eτ) is well known.

Here, τ=C−R, and this value is called a time constant. According to the previous formula, when 1=0, V. It can be seen that =0. Further, it is possible to obtain a change state that increases according to an exponential function according to the elapsed time t after a constant vI is applied. Therefore, this time constant circuit is often used in signal waveform conversion circuits such as differentiating circuits and integrating circuits.

[Invention or problem to be solved]

When the circuit in Figure 4 is used as an integrating circuit, for example, when it is necessary to make the value of τ extremely large, C and R
Is it necessary to increase the values for each separately or for both?

At that time, when a time constant circuit was constructed on the substrate of a semiconductor integrated circuit, the size of the element could not be increased arbitrarily, and there was a drawback that the upper limit was fixed. Furthermore, due to the manufacturing technology of semiconductor devices, the values of C and R vary widely, and since there is no correlation between the two values, it is extremely difficult to design and manufacture a time constant circuit with accurate values.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and to provide a time constant circuit that can obtain an equivalently large value by changing the circuit configuration without making the resistive element or capacitive element particularly large.

[Means to solve the problem]

FIG. 1 is a diagram showing the basic configuration of the present invention. In FIG. 1, 1-1 is the first input terminal, 12 is the second input terminal, 2 is the output terminal, 3 is the ground terminal, 4 is the resistive element, and 6 is the entire capacitance of the time constant circuit according to the present invention. , 7 is a capacitive element in the circuit 6, and 8 is a signal polarity inversion amplifier in the circuit 6.

The other end of the resistor element 'F4 whose one end is connected to the first input terminal 1-1 is connected to one end of the capacitive element 7, and the other end of the capacitive element 7 is connected to the second input terminals 1-2, and a time constant circuit in which one end of the capacitive element is the signal output terminal 2,
The present invention has the following configuration. That is, □″capacitive element 7
Connect one end of the signal polarity inverting amplifier 8 to the input terminal of the signal polarity inverting amplifier 8,
The other end of the capacitive element 7 is connected to the output terminal of the amplifier 8 described above.

It can be replaced by a circuit. ′ [Function] In the circuit shown in FIG. 1, the amplifier 8
The change in the potential at the input terminal of the amplifier 8 and the change in the potential at the output terminal of the amplifier 8 have exactly the opposite relationship and are equal to the book of .G). Therefore, the resistance value of resistance element 4 is R
Then, the time constant of this circuit is (R-C-G). Therefore, the area where the amplifier 8 is configured on the board etc.
If it is smaller than the area that forms a large capacitance (CG),
Saves space on the board.

Next, as shown in Fig. 2, a combination circuit is made of a resistive element 4, a switch 4I, and a capacitive element (capacitance value C'), and when the switching frequency of the switch 41 is f'c, the resistance value is equivalently ni 1/
(C' ・fc). Therefore, the formula for determining the time constant of this circuit is (CG)/(C'fc), which can be expressed only by the ratio of capacitances.

〔Example〕

FIG. 3 is a diagram showing the configuration of an embodiment of the present invention.

In Fig. 3, 42 is a capacitive element whose capacitance value is CI, 43
-1.43-2 is an electronic switch like a transistor,
44 is an inverter, 45 is a pulse generator with a repetition frequency fc, 81.82 is an operational amplifier, especially the former operates as a voltage follower, 83.84 is a resistor element,
When the value of the element 84 is r, the element 83 has a value of G-r (here, G represents the gain of the amplifier 82), and the electronic switch 43-1.43-2 is controlled by the output of the pulse generator 45. Since it is turned on and off alternately, in combination with the capacitive element 42, it operates isometrically as a resistive element. Third
When configured as shown in the figure, the resistance value R of the part that operates as a resistive element is R=l/(C1・fc), and the capacitance value C of the part that operates as a capacitive element is C=02.
G (Here, 02 represents the value of the capacitive element 7.) At this time, the time constant τ can be expressed as the ratio τ=C−R°=(C2·G)/(C1·fc).

After C, C2 are determined, the value of τ can be controlled by changing fc, which is effective in adjusting the time constant.

〔Effect of the invention〕

In this manner, according to the present invention, since the time constant is determined by the ratio of the capacitive elements constituting the circuit, a highly accurate value can be obtained. Furthermore, when changing the value of the time constant, it can be easily done by changing the switching frequency of the switch that opens and closes the connection with the capacitive element. Furthermore, when such time constant circuits are collectively constructed on a substrate using semiconductor manufacturing technology, the layout area can be extremely small compared to conventional circuits when obtaining a large time constant. In addition, even if variations occur in the capacitive element manufacturing technology, the tendency of the variations is the same, so accurate time constant values can be easily designed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle configuration of the present invention, Fig. 2 is a diagram showing another configuration of the present invention, Fig. 3 is a diagram showing the configuration of an embodiment of the present invention, and Fig. 4 is a diagram showing the conventional time constant. It is a diagram showing a circuit. 1-A Word input terminal 2-Signal output terminal 3--Ground terminal/resistance element Overall indication of the capacitance of the time constant circuit Capacitive element signal polarity inversion amplifier Patent applicant Fujitsu Ltd. Representative Patent attorney Suzuki Eisuke Figure 1 Figure 2

Claims (1)

[Claims] 1. The other end of a resistive element (4) whose one end is connected to the first input terminal (1-1) is connected to one end of a capacitive element (7), The other end is connected to the second input terminal (1-2), and one end of the capacitive element (7) is connected to the output terminal (2-2).
), one end of the capacitive element (7) is connected to the input terminal of the signal polarity inverting amplifier (8), and the other end of the capacitive element (7) is connected to the output terminal of the amplifier (8). A time constant circuit characterized by: 2. A time constant circuit characterized in that the resistive element in the time constant circuit according to claim 1 is constituted by a switch having a switching terminal connected to another capacitive element. 3. The switch in the time constant circuit according to claim 2,
A time constant circuit characterized by being opened and closed by a signal with a variable period.