JPH0220012B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pseudo-impedance circuit that includes a feedback circuit having a predetermined voltage transfer function (hereinafter simply referred to as a transfer function) and realizes a wide range of impedances corresponding to the transfer function.

Conventionally known generators and NICs
(Negative Impedance Converter) has an impedance conversion function or a negative impedance conversion function depending on the impedance added to these circuits. However, since a large number of transistors or operational amplifiers are used to realize the generator and NIC, there is a certain limit to the usable frequency due to the frequency characteristics or phase delay characteristics of these elements. For example, if we look at this with respect to a gyrator, if it is an ideal gyrator, its F parameter should be F = 0 G ^-1 G 0, but in reality it is the first row, first column component and the second row, second column component. contains unnecessary elements. Furthermore, the constant G also has frequency characteristics. This is due to the high gain amplifier used to implement the gyrator.

Therefore, an object of the present invention is to provide a generator and NIC with a simple configuration without using a high gain amplifier.
The purpose of the present invention is to provide a pseudo-impedance circuit that can be used up to high frequency ranges.

The pseudo-impedance circuit according to the present invention includes a low gain (for example, amplification factor=1) amplifier circuit, a first feedback circuit responsive to a predetermined transfer function H(S), and a first feedback circuit connected in parallel to the first feedback circuit element. and a connected second feedback circuit. If the conversion coefficient defined by the second feedback circuit is R _K , then the impedance Z _io seen from the input end of the low gain amplifier circuit is
is given by the following equation. The voltage and current in the frequency domain in the following explanation are incremental (alternating current) currents, and the fixedly existing direct current component is ignored.

Zin=R _K /H(S) Therefore, arbitrary inductive impedance and capacitive impedance can be obtained as Zin. Furthermore, the above
By appropriately selecting R _K and H(S), a negative impedance of Zin=±R±jX can be obtained.

Hereinafter, the present invention will be explained in detail using the drawings.

FIGS. 1A and 1B are diagrams showing circuits required as a prerequisite for explaining the present invention.

In FIG. 1A, an amplifier A with an amplification factor of 1
A voltage Ei is applied to the input terminal of. Also, a feedback element T ((open-ended voltage transfer which is a function of complex frequency S) transfer function H(S) connected to the output terminal of amplifier A)
) is feedback connected to the input terminal of the amplifier A via the base and collector of the transistor Q. Furthermore, the emitter of transistor Q is a resistor.
Grounded via Ra.

Since the amplification factor of amplifier A is 1, the voltage applied to the base of transistor Q is Ei·H(S) since the input impedance of the base is sufficiently high and can be regarded as infinite. Therefore, if the resistance value of the resistor Ra is (Ra), the current Ia flowing through the resistor Ra is Ia=Ei·H(S)/(Ra). Therefore, the input impedance Zin considering amplifier A is given by the following equation.

Zin=Ei/Ii=(Ra)/H(S) (1) However, ignoring the base current of transistor Q and the input current of amplifier A, let Ii=Ia.

As shown in the first equation above, it is clear that the circuit shown in FIG. 1A performs the same function as a conventionally known impedance converter using a gyrator.

Amplifier A and transistor Q shown in FIG. 1B have the same configuration as used in FIG. 1A. However, the feedback element T shown in FIG. 1A is not used, and instead the transistor Q
A common connection point of resistors Rb and Rc connected in series to the emitter of the amplifier A is connected to the output terminal of the amplifier A. Further, the base of transistor Q is grounded. In this circuit as well, since the amplification factor of amplifier A is 1, the current Ib flowing through resistor Rb is Ib=Ei/(Rb). Here, (Rb) represents the resistance value of resistor Rb. Therefore, since Ii=-Ib, the input impedance Zin is given by the following equation.

Zin=Ei/Ii=Ei/−Ei/(Rb)=−(Rb)……(
2) As shown in the second equation above, it is clear that the circuit shown in FIG. 1B realizes negative resistance in the same way as when using NIC.

In order to combine the functions of FIG. 1A and FIG. 1B described above, these two figures may be superimposed. The circuit shown in FIG. 2 is thus obtained. However, in Figure 2, an extra resistor _R3 is added,
These do not change the effect of the above-mentioned superimposition.

FIG. 2 is a block diagram showing a pseudo-impedance circuit according to one embodiment of the present invention. Now, the H parameters of transistor Q are hie (input impedance), hoe (output admittance), and hfe (current amplification factor).
shall be. Further, the current flowing into the collector in response to the voltage Ei·H(S) applied to the base of the transistor Q is assumed to be I ₁ +ΔI ₂ . However, ΔI ₂ represents the current flowing into the collector when the potential of the base is zero. Further, the current flowing into the power supply through the resistor Rc is designated as _I3 , and the current flowing through the resistor _R1 due to the potential generated at the common connection point J of the resistors _R1 , _{R2, and R3 is} designated as _I4 . shall be. Therefore, the current Ii is Ii=I ₁ +△I ₂ +I ₃ −I ₄ ………(3) However, gm ₁ = hfe−hoe・Rv/hfe・Rv+Rv′ gm ₂ = (hie+Rv)hoe/hfe・Rv+Rv′ gm ₃ =hie・hoe+hfe/hfe・Rv+Rv′ Rv=R ₁ +R ₂ R ₃ Rv′=(1+hie・hoe) Rv+hie αv=R ₂ /R ₂ +R ₃ Generally, hfe≫1 and hie・hoe<1, so gm ₁ ≒1/Rv gm ₃ ≒1/Rv. Therefore, if the resistor R ₃ is adjusted so that gm ₂ +1/Rc = αv·gm ₃ , Ii = gm ₁ (Ei·H(S)) from the third equation. And the input impedance Zin is Ei/Ii
Therefore, using the approximation formula for gm ₁ described above, Zin≒Rv/H(S) (4).

In the fourth equation above, Rv is determined by the resistors R ₁ , R ₂ , and R ₃ , so the function shown in the first equation can be realized by this embodiment.

Furthermore, it is clear from the third equation that when I ₄ is increased at the same time as H(S) is decreased, the current Ii becomes negative. This means that the input impedance Zin becomes a negative resistance.

Although the present embodiment has been described assuming that the amplification factor of the amplifier A is 1, it is not limited to this embodiment. However, if an amplifier with a high amplification factor is used, problems similar to those of the conventional gyrulator and NIC will occur, and one of the advantages of the present invention will be lost.

FIGS. 3A, 3B, and 3C are diagrams showing an example of a circuit that can be used in place of the transistor Q shown in FIG. 2. That is, Fig. 3A shows FET,
Figure 3B shows a combination of a transistor and an operational amplifier.
Figure 3C is a combination of FET and operational amplifier.
Although the use of these circuits contributes to realizing accurate H(S), it has the disadvantage that the frequency characteristics deteriorate due to the complicated circuit configuration.
Therefore, when simplifying the circuit and improving frequency characteristics, the transistor Q shown in FIG. 2 is preferable.

FIG. 4A shows the negative resistance (-
1K ohm) and capacitor (16PF) in parallel connection.”
It is a circuit diagram for forming an impedance consisting of (for alternating current). In this diagram, the transistor
For Q ₁ and Q ₂ , 2N5943 manufactured by Motorola is used. In the circuit shown in this figure, the base of transistor _Q2 is connected to a capacitor so that H(S)=0.
Grounded via _C4 and _C5 . Also, in order to realize negative resistance, R ₃ = 0 (second
(see figure). The constants of each resistor and capacitor are as shown below.

C ₁ = 0.01μF C ₂ = 1.0μF C ₃ = 1.0μF C ₄ = 1.0μF C ₅ = 0.047μF C ₆ = 1.0μF R ₁ = 3.16K ohm R ₂ = 1K ohm R ₃ = 10K ohm R ₄ = 5K Ohm R ₅ = 274 ohm R ₆ = 2.61K ohm R ₇ = 1K ohm R ₈ = 1K ohm With the constants shown above, an impedance obtained by connecting -1K ohm and 16PF in parallel can be obtained. In addition,
This 16PF is caused by the stray capacitance of transistors _Q1 and _Q2 .

FIG. 4B is a galley representing the frequency characteristics of the circuit shown in FIG. 4A. In this figure, the left vertical axis is the absolute value of the impedance (unit: K ohms) obtained in Figure 4A, the right vertical axis is the phase angle of the impedance (unit: degrees), and the horizontal axis is the frequency (unit: :
MHz).

As described in detail above, since arbitrary L, C, and R can be configured using the pseudo-impedance circuit according to the present invention, it is possible to realize a small-sized element integrated into an IC. For example, this is particularly useful when a programmable dummy is constructed by continuously changing L, C, and R using a voltage-controlled resistor. Furthermore, compared to conventional gyrulators and the like, the circuit configuration is simple and a high gain amplifier is not required, so the frequency characteristics are significantly improved.

[Brief explanation of drawings]

1A and 1B are circuit diagrams as a premise for explaining the present invention, FIG. 2 is a block diagram showing an embodiment of a pseudo impedance circuit according to an embodiment of the present invention, FIGS. 3A and 3B, FIG. 3C is a diagram showing an example of a circuit that can be used in place of the transistor Q shown in FIG. 2, and FIG. 4A is a diagram showing an example of a circuit that can be used in place of the transistor Q shown in FIG. FIG. 4B is a graph showing the frequency characteristics of the circuit shown in FIG. 4A. A: amplifier, T: feedback element with transfer function H(S).

Claims (1)

[Claims] A pseudo-impedance circuit composed of the following first-order (a) to (f). (a) First terminal. (b) Grounded second terminal. the second terminal and the first
A pseudo impedance is formed between the terminals. (c) An amplifier with an amplification factor of 1, which has the first terminal as an input terminal, an output terminal, and an input resistor. (d) A transistor having an emitter terminal, a base terminal, and a collector terminal connected to the first terminal. (E) A feedback element having a desired voltage transfer function that connects the output terminal and the base terminal. (f) Connect the output terminal and the emitter terminal,
a resistive network for making the pseudo impedance proportional to the reciprocal of the transfer function;