JPS601967B2 - capacitance circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitance circuit realized by a simple circuit, and in particular to a grounded capacitance circuit.

In recent years, various circuits using integrated circuit operational amplifiers (obeamps) have been proposed and put into practical use.

One such type of circuit is the inductance and capacitance implemented using an OBE amplifier. Among these, an inductance circuit has already been proposed by the present applicant in Japanese Patent Application No. 53-63947, and therefore the present invention relates to a capacitance circuit. Figure 1A shows a conventional capacitance circuit, and Figure 1B shows its equivalent circuit, where OP is an obeamp, R, , R2, and R3 are resistors, and C
, is the capacitance, and the values of the combined capacitance Co and the series resistance RS of this circuit are given as follows.

C.

= Climb - CI, RS; R3 Therefore, the capacitance circuit in Figure 1 essentially includes a series resistance RS, and RS
It is impossible in principle to set the value to 0.

On the other hand, in normal circuit design, capacitance is generally treated as lossless, so the presence of a series resistance component is a major drawback in practice. SUMMARY OF THE INVENTION The present invention therefore aims to improve the above-mentioned drawbacks of the prior art and provides a capacitance circuit that does not include a lossless series resistance component.

This purpose is achieved by a simple circuit consisting of one amplifier, three resistors and two capacitors. FIG. 2A shows a circuit diagram of a capacitance circuit according to the present invention, and FIG. 2B shows its equivalent circuit.

In FIG. 2A, reference number 1 is an obeamp, which has a negative input terminal la, a positive input terminal lb, and an output terminal lc. A first resistor 2 (admittance y2) is connected between the negative input terminal la and the output terminal lc, and a first capacitance 5 (admittance Y5) is connected between the positive input terminal lb and the output terminal lc. Further, a second capacitance 6 (admittance Y6) is connected between the positive input terminal lb and the ground point, and a second capacitance 6 (admittance Y6) is connected between the negative input terminal la and the positive input terminal lb.
A series circuit including a resistor 3 (admittance Y3) and a third resistor 4 (admittance Y4) is continued. A composite capacitance Co is obtained between the connection point 7 and the ground point 8 of the series circuit. Input admittance Yin of the circuit of Fig. 2A
'Given by the following equation. Yin=Y2Y6(Y
40Y3) -Y3Y50Y4Y20Y2Y6 Here, if Y3Y5=Y2Y6, the above equation becomes as follows.

Yin=Y6 (1 cross) Furthermore, if we set Y2=Y3, Y5=Y6=sC (where s is i), then Yin! SC (10 min), which is the equivalent circuit shown in Figure 2 B'.

Here, in order to make the capacitance value variable, either one of the resistors 3 and 4 may be made a variable resistor. As is clear from the above analysis, the capacitance circuit according to the present invention does not include any series resistance and can obtain an infinite Q. As explained above using the embodiments, according to the present invention, a capacitance circuit without series resistance can be obtained with a simple circuit.

[Brief explanation of drawings]

Figure 1A shows a capacitance circuit according to the prior art;
FIG. 2B is an equivalent circuit of FIG. 1A, FIG. 2A is a capacitance circuit according to the present invention, and FIG. 2B is an equivalent circuit of FIG. 2A. 1; obeamp; 2, 3, 4; resistance; 5, 6; capacitance. Fig. 2

Claims (1)

[Claims] 1. An operational amplifier, a first resistor connected between the negative input terminal of the operational amplifier and the output of the operational amplifier, and a first resistor connected between the positive input terminal of the operational amplifier and the output of the operational amplifier.
a series circuit including a capacitance, a second capacitance connected between the positive input terminal and a ground point, and a second resistor and a third resistor connected between the negative input terminal and the positive input terminal, A capacitance characterized in that the product of the first resistor and the second capacitance is approximately equal to the product of the second resistor and the first capacitance, providing a capacitance between a connection point of the series circuit and a ground point. circuit. 2. The capacitance circuit according to claim 1, wherein the first capacitance and the second capacitance are equal.