JPS5864817A - Gyrator - Google Patents

Abstract

PURPOSE:To set the capacitance of a capacitor small and to increase the Q of an equivalent inductance, by using a resistor and a capacitor for each admittance of a gyrator circuit as specified. CONSTITUTION:Y4-Y8 are admittances of each element, 1-3 are nodes of this circuit, and V2, V3 are voltages at nodes 2 and 3 respectively. The relation between input terminals Vin and V2 of input terminals 1a, 1b and an output Vout of an operational amplifier 4 is expressed in equations 1 and 2. Thus, an input impedance Zin is expressed in equation 3. Where Y5Y7=Y6Y8 is satisfied, equation 3 is simplified into equation 4. Taking Y4=SC, Y5=1/R5 and Y8=1(that is, resistors R5, R8 are used for Y5, Y8 respectively and a capacitor C is used for Y4) in equation 4, a series circuit of R and L is obtained as given by equation 5. In equation 5, the resisters R5, R8 are included in the imaginary part and the capacitance value of the capacitor C can be set arbitrarily independently of the Q of the equivalent inductance to some extent. Thus, said Q can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noyerator circuit that can provide a wide dynamic range.

FIG. 1 shows a circuit that has been widely used as a gyrator with a small number of components, a wide dynamic range, and a single operational amplifier.

In the circuit shown in FIG. 1, YIYzeYs is the admittance of each element, vin is the input terminal voltage between the input end terminal 1gb, 4 is the operational amplifier, and vout is the output of the operational amplifier 4. The input admittance Yin in the circuit of FIG. 1 is expressed by the following equation.

There is the following relationship between vout.

y, V, n= −y 2vout−−−−−−=
-= (2) Also, from equations (1) and (2), Yin becomes as shown in the following equation (3).

That is, Yl and Y3 are each resistor R1#, and capacitor C is used for R3 and y2), then R as shown in the following equation (4)
It becomes a parallel circuit of 1yR3 and inductance L given by L=RIR3C.

Y=±100 in R1R35CR1R3"' (4) Also, the output voltage V.ut of the operational amplifier 4 at this time is given by the following equation from equation (2).

vout”SCR,”in...
......-(5) Therefore, as is clear from equation (5), the output voltage V of the operational amplifier 4 of the circuit shown in FIG.

ut is smaller than vin. Furthermore, in equation (4), in order to increase the Q value of the equivalent inductance, the real part must be increased, and therefore R1 and R3 must be decreased. On the other hand, when the inductance L given by L=RIR3C is kept constant, the capacitance of the capacitor C becomes large as R1 and R3 are made small. Therefore, it becomes a big obstacle when converting the circuit into an IC.

Also, as is clear from equation (4), the circuit shown in FIG.
When creating an equivalent inductance, a real number component is always included, so there is a drawback that it is impossible to create an equivalent inductance with a high Q value.

The purpose of the present invention is to eliminate the disadvantages of the conventional circuit in that the capacitance value of the capacitor cannot be set arbitrarily and the Q value of the equivalent inductance cannot be set high, as described above in detail. .

FIG. 2 is a circuit diagram of the present invention, Y, IY5 #Y6
v Y7 e Ys is the admittance of each element, 1
゜2.3 is the node of the circuit, v2 is the voltage at node 2, v
3 indicates the voltage at node 3, and the other symbols indicate the same as in FIG. In FIG. 2, the nodal equation for the node 1°2.3 is as follows. (Il indicates the current at node 1) I 1 = (Y4+y8) Vin-y4v2-y8”o
ut ・−・−・−・(6) o=(Y6+Y7)V
2-Y7vout ・・・・・・・-(7)o
=-Y4vin + (Y4 +Y5)V2
-.(8) Next, when the relationship between vin and v2#vout is determined from equations (7) and (8), the following equation is obtained.

Therefore, the input impedance zin of the circuit shown in FIG.
The expression (6) is as follows.

zin=death=π發璼璔姶安口・・・・・・・・・αp
Here, if Y5Y7=Y6Y8 is satisfied, the formula Q
l) is a simple equation as shown below.

zin =-L (t+yu) ・・・・・・・・・
...(2) ys ys 1 Also, in equation (2), if y, = sc, y5-6, Y, = old (that is, resistors R5 #RII are used for Y5 #Y8, and capacitor C is used for Y4), R given by the following formula
, L becomes a series circuit. --”in = R@ (1+
5CRs) -++++-・+・・+a
First, v2., which is the voltage at the input and output of the operational amplifier 4, determines the dynamic range of this circuit. vOu
t is given by equation (9), α0].

(In this case, the voltage v3 at node 3 is also equal to v2) Here, Y7"KY6, YB==[Ys.

When comparing Equation (4) and Niαbu, Equation (4) has R1 and R3 in the real part and imaginary part, and the capacitor C
The capacitance value and the Q value of the equivalent inductance are closely related, and if the Q value of the equivalent inductance is increased, the capacitor C will also become larger. On the other hand, if the equation is 1, then the resistance R,
, R, enters the imaginary part and the equivalent inductance Q
The capacitance value of the capacitor C can be set arbitrarily regardless of the value to some extent. Therefore, in the circuit diagram of FIG. 2 which is the present invention, the Q value of the equivalent inductance can be increased and the capacitance value of the capacitor C can be decreased.

Next, as an example, R=1500, L=5.5mH.

In the case of an R, L, C series resonant circuit with C=18000 pF, the conventional circuit shown in FIG. 1 and the circuit according to the invention shown in FIG. 2 are compared.

In the case of the circuit shown in Figure 1, as mentioned above, if Yl and Ys are each resistors RIFR3, and Y2 is a capacitor C, then the resistance R1 = Rs = 300Ω, so L = :CRI
The capacitance value of capacitor C is 61000 pF from R3.

On the other hand, in the case of the circuit of the present invention shown in FIG. 2, Y4 is the capacitor C%
ys t ya l y, , YB are each resistor R5+
R6* R7e R8, R7=R,=1500
becomes. Also, if R, = R, = 15 is set to Ω, L =
From CRs Rm, the capacitance value of capacitor C is 2443p
F, which is extremely small compared to that in FIG.

As explained above, the noyerator circuit of the present invention has the advantage that the capacitance of the capacitor C can be arbitrarily set to a small value and the Q value of the equivalent inductance can be increased. Therefore, even when the circuit is integrated into an IC, there is no problem caused by the capacitance of the capacitor.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional gyrator circuit.
The figure is a circuit diagram of a gyrator circuit according to the present invention. 1.2.3... Circuit node, 4... Operational amplifier, 1
a-1b...input terminal, vin...input terminal 1a-
Input terminal voltage between 1b, vout...output of operational amplifier 4, y, I y5 t Y@e y, tys・
... Admittance, v2 ... Voltage at node 2, v
3... Voltage at node 3. Patent applicant Oki Electric Industry Co., Ltd.

Claims (1)

[Claims] Connecting between the input terminal of the circuit and the output terminal of the operational amplifier via a first resistor, and connecting the inverting side input terminal of the operational amplifier and the output terminal of the operational amplifier via a second resistor. The other end of a third resistor whose one end is grounded is connected to the inverting input terminal of the operational amplifier, and the input terminal of the circuit and the non-inverting input terminal of the operational amplifier are connected via a capacitor. A gyrator comprising a circuit in which one end of a fourth resistor is grounded and the other end is connected to the non-inverting input terminal of the operational amplifier.