JPS61251311A - Impedance converting circuit - Google Patents

Abstract

PURPOSE:To obtain the K-multiple equivalent impedance of an impedance element by feeding back negatively a current flowing to the impedance element to a current converting circuit converting the current into a prescribed ratio (1/K). CONSTITUTION:An input voltage eIN from input terminals 1A, 1B is fed to a buffer circuit 3 being a voltage followr circuit via an adder circuit 2. The output of the buffer circuit 3 is fed to a current converting circuit 5 via the impedance element 4 having an impedance Z1. Thus, the current i1 flowing through the impedance element 4 is converted into 1/K (current i0) from the current converting circuit 5 and outputted. Thus, the equivalent impedance between the input terminals 1A, 1B is KZ1.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to an impedance conversion circuit suitable as a configuration of an IC circuit.

B0 Summary of the Invention This invention converts the magnitude of the current flowing through the impedance element by a predetermined ratio (1/K) by applying an input signal to both ends of the impedance element via a voltage follower circuit, and returns the current to the impedance element. By doing so, an equivalent impedance of K-Zl is formed for the fixed impedance z1 of the impedance element.

C1 Prior Art In monolithic ICs, it is well known to fabricate transistors, resistors, small capacitors, wiring patterns, etc. on a semiconductor substrate. It is technically difficult to form inductor components and large capacitance capacitors,
When necessary, lead-out terminals were provided and connected to the outside of the package.

D0 Problems to be Solved by the Invention In conventional ICs, when a large capacitance capacitor is required, it is attached externally, resulting in an increase in cost due to an increase in the number of terminal pins.

In addition, due to the large temperature characteristics and variations in absolute values of the resistance within the IC, when configuring a time constant circuit built into the IC or a filter circuit built into the IC, variations in characteristics such as cut-off characteristics, and variations in temperature characteristics may occur. Problems such as stability arose.

Therefore, an object of the present invention is to be able to form an equivalent impedance that is the fixed value Z1 of the impedance element multiplied by
An object of the present invention is to provide an impedance conversion circuit that can easily form a large capacitance in a C.

Another object of the present invention is to provide an impedance conversion circuit that can cancel the influence of the temperature characteristics of the elements in the rc by giving the coefficient K a characteristic.

Still another object of the present invention is to provide an impedance conversion circuit that can configure a filter with a variable cutoff frequency by varying the coefficient K.

Means for Solving the E0 Problem The one-end grounded configuration of the present invention has a first input terminal IA, a second input terminal IB, and a signal addition point 2 connected to the first input terminal IA. , an impedance element 4 to which an input signal supplied to the first input terminal IA and the second input terminal IB is supplied via the voltage follower circuit 3;
Convert the current i flowing into the output current 10 at a predetermined ratio,
A current conversion circuit 5 that feeds back the output current 10 to the signal addition point 2
An impedance conversion circuit characterized by comprising:

The two-terminal floating type configuration of the present invention has a first input terminal 1 and a second input terminal 1), and a first input terminal l.
and a signal summing point 2.12 connected to each of the first input terminal 1 and the second input terminal 1).
The input signal supplied to the impedance element 4 is supplied to both ends thereof via the voltage follower circuits 3 and 13, and the current i flowing through the impedance element 4 is converted into an output current 10 at a predetermined ratio, and an output current i6 signal addition point 2,1
This impedance conversion circuit is characterized in that it includes a current conversion circuit 4 that feeds back to each of the impedance conversion circuits 2 and 2.

Current 1) flowing through F1 working impedance element 4 and output current 10
By converting into the relationship (io = it /K), the equivalent impedance Z2 seen from the input terminal can be expressed as K
It can be Z. Therefore, the current conversion ratio K in the current conversion circuit allows a capacitance so large that it cannot be formed in an IC to be formed, and this conversion ratio k allows
It is possible to form a variable impedance, and further, by using the conversion ratio K, it is possible to realize a filter with variable frequency characteristics.

G. Example G1. Basic configuration The basic configuration of this invention will be explained below.

FIG. 1 shows a configuration of one end grounded type, in which an input voltage elN is supplied to an input terminal IA and a grounded input terminal IB. Input terminal IA is connected to one input terminal of adder circuit 2 . The adder circuit 2 is configured to add currents, and the output signal of the adder circuit 2 is supplied to a buffer circuit 3 with a gain of l. The buffer 3 has a voltage follower type configuration with substantially infinite input impedance, and a fixed impedance element 4 is connected between the output terminal of the buffer circuit 3 and the current conversion circuit 5. The current conversion circuit 5 has an input impedance Zin of approximately O and an output impedance Zout of approximately infinity.

If the value of the impedance element 4 is Z, the current i flowing through this impedance element 4 is e1N/Z, = 1
)...■. This current 1) is supplied to the current conversion circuit 5, and from the current conversion circuit 5, to = i + /K...■,
An output current multiplied by 1/1 is generated. Therefore, the equivalent impedance Z between the input terminals IA and 18 of the circuit configuration shown in FIG. 1 is Zt=eIN/10=KZ, ・・
・It becomes ■. As can be seen from equation 0, according to the present invention, the fixed value ZI of the impedance element 4 can be increased in accordance with the conversion ratio K of the current conversion circuit 5.

FIG. 2 shows another example of the basic configuration of the present invention, that is, a two-terminal floating type configuration in which neither input terminal 1 nor input terminal 1) is grounded. One input terminal 1 is connected to one input terminal of an adder circuit 2, and an output terminal of the adder circuit 2 is connected to an input terminal of a buffer circuit 3. The other input terminal 1) is similarly connected to one input terminal of the adder circuit 12, and the output terminal of the adder circuit 12 is connected to the input terminal of the buffer circuit 13.

A fixed impedance element 4 is inserted between the output terminal of the buffer circuit 3 and the output terminal of the buffer 13. The input impedances of the buffers 3 and 13 are approximately infinite, and when the input terminal eIN is applied between the input terminals 1 and 1), the current 1) of the above-mentioned equation 0 flows through the impedance element 4.

A current 1) flowing through this impedance element 4 is converted by a current conversion circuit 5 into a current 1) shown by equation 0. The current conversion circuit 5 has a substantially infinite output impedance, and a current 10 is supplied to each of the adder circuit 2 and the adder circuit 12. Equivalent impedance z seen from input terminals 1 and 1) of the two-terminal floating type circuit shown in Fig. 2
2 becomes KZ, similar to the above-mentioned equation 0.

As described above, the circuit configuration using the equivalent impedance Zz for the fixed impedance Z1 has the following characteristics.

First, by changing K using the current conversion circuit 5, the impedance can be varied. Therefore, it is possible to realize a filter with a variable cutoff frequency.

Second, K can be determined so that arbitrary temperature characteristics and fluctuations can be added to the equivalent impedance Z2, and temperature characteristics and fluctuations of elements connected to the equivalent impedance Z2 can be canceled.

Thirdly, the value of the capacitance built into an IC circuit is limited in terms of area. However, in this invention, Z,
When the capacitance is built into an IC circuit, a capacitance K times larger can be achieved.

The above features of the present invention can be more easily understood from the examples described below.

G2. Two-terminal floating type capacitance conversion circuit FIG. 3 shows the configuration of an embodiment of the two-terminal floating type capacitance conversion circuit of the present invention, in which a capacitor is connected between the emitters of transistors 21 and 22. 20 are connected.

The bases of transistor 21 and transistor 22 are led out as input terminals 31 and 32, respectively. The transistors 21 and 22 have a voltage follower type configuration, and the second
This corresponds to buffer circuits 3 and 13 in the figure.

Capacitor 20 corresponds to impedance element 4 .

Also, the emitter of the transistor 21 and the transistor 2
A constant current source is connected to each of the two emitters. A constant current source consisting of a transistor 25 is connected between the emitter of the transistor 21 and ground. transistor 22
A constant current source consisting of a transistor 26 is connected to the emitter of the transistor 26 .

A diode 28 to which a constant current I is supplied from a constant current source 28 is inserted between the base emitter of the transistor 25 and the transistor 260.

At each emitter of these transistors 21 and 22,
A constant current ■ flows.

The collector of the transistor 21 is connected to the power supply terminal 34 through the collector and emitter of the transistor 29, and the collector of the transistor 22 is connected to the power supply terminal 34 through the collector and emitter of the transistor 30. The power supply terminal 34 is supplied with a power supply voltage of Vcc.

At the bases of the transistor 29 and the transistor 30,
A DC voltage source 33 is connected in common.

A connection point between the collector of transistor 21 and the emitter of transistor 29 is connected to the base of transistor 23, and a connection point between the collector of transistor 22 and the emitter of transistor 30 is connected to the base of transistor 24. The emitters of these transistors 23 and 24 are commonly connected, and this emitter common connection point is connected to the collector of a transistor 36.

Transistor 36, transistor 35 and transistor 3
7, the bases are commonly connected to each other, and a diode 39 is commonly connected between the base and emitter of these transistors.
is inserted. A constant current I0 is supplied to the diode 39 by a constant current source 38. These transistors 35 and 37 each constitute a constant current source with a constant current I0, and the transistor 36 has a constant current 2. This constitutes a constant current source.

The power supply terminal 34 and the emitter of a PNP transistor 40 are connected, and the collector of the transistor 40 is connected via a diode series connection 44. It is connected to the collector of a transistor 35 constituting a constant current source. Similarly, the power supply terminal 34 and the emitter of a PNP transistor 41 are connected, and the collector of the transistor 41 is connected via a diode series connection 45. Transistor 3 constituting a constant current source of
7 collector.

A diode 42 to which a constant current of 2Io is supplied by a constant current source 43 is commonly inserted between the base and emitter of the PNP transistors 40 and 41. Each of these transistors 40 and 41 has a constant current of 2. Configure a constant current source. A connection point between the diode series connection 44 and the collector of the transistor 35 is connected to the base of the transistor 21. A connection point between the diode series connection 45 and the collector of the transistor 37 is connected to the base of the transistor 22.

The transistors 23, 24, 40, 41 have a configuration corresponding to the current conversion circuit 5 in FIG.

That is, the current flowing through the capacitor 20 is 1. is converted into a current 1, which is fed back to input terminals 31 and 32, respectively.

In the embodiment of the present invention described above, when the input voltage eIIl supplied to the input terminals 31 and 32 is, the equivalent impedance between the input terminals 31 and 32 is 2! is obtained as follows.

First, the impedance of the capacitor 20 is 1/Z+-
C3, and therefore the current 1) flowing through the capacitor 20 is il = C5-e+N. For example, when the potential of the input terminal 31 is higher than the potential of the input terminal 32, the collector current of the transistor 21 becomes N+t+), as shown in FIG.
At 0, the current i.

flows. In this case, a current of (■.-10) flows through the collector of the transistor 23, and a t current of (■.+to) flows through the collector of the transistor 24.

The sum of the base-emitter voltage of transistor 29 and the base-emitter voltage of transistor 23 and the base-emitter voltage of transistor 30.

Since the sum of the base-emitter voltages of the transistor 24 and the sum of the voltages between the base and emitter of the transistor 24 are equal, the relationship between the signal current 10 and i is as follows. The equivalent impedance z2 is Zz = e + N/10 = K (1/C3).
Therefore, a capacitance increased by K times can be formed by the ratio K of the constant current I and Io. For example, constant current ■.

If it is made 10 times the constant current ■, a capacity 10 times larger can be formed. Furthermore, K allows a variable capacitance circuit whose capacitance is variable to be configured.

G3. Resistance conversion circuit FIG. 4 shows the configuration of a two-terminal floating type resistance conversion circuit constructed by applying the present invention.

In place of the capacitor 20 described above, a resistor 61 is connected between the emitter of the transistor 21 and the emitter of the transistor 22. The other configurations are the same as in FIG. 3.

In the configuration shown in FIG. 4, when the value of the resistor 61 is R, the equivalent resistance RIM between the input terminal 31 and the input terminal 32 is RIN=(I/I.)·R−K−R. Therefore, a resistance that is variable depending on the current ratio K can be formed.

G4. Temperature Characteristics and Variation Compensation As shown in FIG. 5, the equivalent impedance, which is the variable capacitance component of the configuration shown in FIG. 3, is 2! and the resistor R can constitute a bypass filter. Here, resistance R
7! Consider the case where l<resistance within the IC and it varies to R(1+Δ) due to temperature characteristics, variations in absolute value, etc.

When the current conversion ratio K in this invention has a characteristic such that K(1+Δ), the transfer function (e0/e, M) of this bypass filter becomes 1 +CR3 from the relationship. As is clear from the above equation, the transfer function is not affected by variations in the absolute value of the resistance R within the IC or by variations due to temperature.

In order to give the current ratio K the characteristic of K(L+Δ), it is sufficient to set I-A/R (external resistance) 16 =B/R (internal resistance) when each of A and B is a constant. In other words, R (external resistance) hardly changes due to temperature and can be made to have no variation in absolute value. R (internal resistance) may be set to a value having the same variations and temperature fluctuations as the resistance R inside the IC in FIG.

Generally, variations in resistance on the same semiconductor substrate have the same tendency.

Furthermore, in the bypass filter shown in FIG.
When is a stable resistance outside the IC, the currents ■ and ■. It is possible to use either a method in which the ratio K is stabilized by determining both of them using external resistances, or a method in which both the currents I and to are determined by internal resistances and the ratio K is stabilized.

Regarding the resistance conversion circuit shown in Fig. 4, ■ is determined by the internal resistance, and ■. By determining RI using an external resistance, the equivalent resistance RI is unaffected by temperature characteristics inside the IC, variations in values, etc.
M can be formed.

G5. Bypass Filter FIG. 6 shows an example of a bypass filter having one end grounded according to the present invention. An input voltage source 51 is connected to an input terminal 31 connected to the base of the transistor 21 . The base of the transistor 22 is grounded via a resistor 50, and a series circuit of a resistor 49 and a diode series connection 45 is inserted between the base of the transistor 22 and the power supply terminal 34. Further, an output terminal 52 is led out from the base of the transistor 22.

The collectors of transistors 21 and 22 are connected to a power supply terminal 34 via collectors and emitters of transistors 29 and 30, respectively. A voltage source 3 is commonly connected to the bases of these transistors 29 and 30.
3 is connected.

Further, the collector of the transistor 23 is connected to the connection point of the resistor 49 and the diode series connection 45, and the collector of the transistor 24 is connected to the power supply terminal 34.

In the configuration shown in FIG. 6, constant current ■ flows through the constant current sources connected to the emitters of transistors 21 and 22, and constant current ■ flows through the constant current sources connected to the emitter connection points of transistors 23 and 24. ,
Constant current ■. flows.

As before, if (K=I/IO), the output voltage e generated at the output terminal 52 by the current 10 taken out to the collector of the transistor 23. is, eo=io ・
R (However, R means the parallel combined resistance of the resistor 49 and the resistor 50.) Also, the output current 10 is io = (1/K) ·i.

= (C3/K) · (e+5-eo), so the output voltage e0 is as follows.

G6. Current-driven low-pass filter FIG. 7 shows a current-driven low-pass filter constructed according to the present invention.

Similar to the above-described bypass filter of FIG. 6, a capacitor 20 is inserted between the emitters of transistors 21 and 22, one constant current source is connected to each emitter of transistors 21 and 22, and one constant current source is connected to each collector of transistors 21 and 22. Transistors 29 and 30 are connected between the terminal and the power supply terminal 34, transistors 23 and 24 are connected to the collectors of transistors 21 and 22, respectively, and 2 is connected to the common connection point of the emitters of transistors 23 and 24. A constant current source is connected.

The collector of the transistor 23 is connected to the power supply terminal 34, and the collector of the transistor 24 is connected to the power supply terminal 34 via the resistor 54. The series connection of this resistor 54, diode series connection 55, and input current source 53 is connected to the power supply terminal 34.
and ground. Diode series connection 55
and the input current source 53 are connected to the base of the transistor 21. Further, an output terminal 52 is led out from the base of the transistor 21. Furthermore, the base of transistor 22 is grounded via DC voltage source 56 .

In the above-mentioned low-pass filter, the converted current 10 is taken out to the collector of the transistor 24. Therefore, when the value of the resistor 54 is R, the output voltage e0 is eo ''R(1)8-t o ).The output current 10 is t6 = (CS/K) ·e.

becomes.

The low-pass filter shown in FIG. 7 has a configuration equivalent to the low-pass filter shown in FIG. 8, and the capacitor in FIG. 8 is (C/K).

G7. Voltage-driven low-pass filter The low-pass filter driven by the input voltage source 51 is
The configuration is shown in the figure. In FIG. 9, the circuit block indicated by 60 is the same as the connection consisting of transistors 21, 22, 23, 24, etc. shown surrounded by broken lines in FIG.

One end of the input voltage source 51 is AC grounded, and the other end is connected to a resistor 57. It is grounded via a diode series connection 58 and a constant current source 59. The connection point between the constant current 57 and the diode series connection 58 is the transistor 2 of the circuit block 60.
4, and the connection point between the diode series connection 58 and the constant current source 59 is connected to the base of the transistor 21 of the circuit block 60, and is also used as the output terminal 52. The resistor 57 converts the input voltage into an input current 1). This input current inN and the output current 10 of the circuit block 60 are combined.

This voltage-driven low-pass filter has a configuration equivalent to the low-pass filter shown in FIG. 10, and the capacitor in FIG. 10 is (C/K).

H0 Effects of the Invention According to the invention, an impedance twice the fixed impedance Z+ can be formed by the conversion ratio K of the current conversion circuit. Therefore, it is possible to realize a large capacity that cannot be formed within an IC.

Further, according to the present invention, a variable impedance element can be realized, and a TC filter with variable frequency characteristics can be realized.

Further, according to the present invention, by providing the conversion ratio K with temperature characteristics and variations, it is possible to cancel the effects of variations in temperature characteristics and values within the IC.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of the basic configuration of the one-terminal grounding type according to the present invention, FIG. 2 is a connection diagram of the basic configuration of the two-terminal grounding type, and FIG. Figure 4 is a connection diagram of a resistance conversion circuit constructed according to the present invention, and Figure 5 is a connection diagram of a resistance conversion circuit constructed according to the present invention.
The figure is a connection diagram used to explain this invention, FIG. 6 is a connection diagram of a bypass filter constructed according to this invention, and FIGS. 7 and 8 are connection diagrams and equivalent equivalents of an example of a low-pass filter constructed according to this invention. The circuit diagrams of FIGS. 9 and 10 are a connection diagram and an equivalent circuit diagram of other examples of the low-pass filter constructed according to the present invention. Explanation of main symbols in the drawings IA, IB, 1.1): Input terminal, 2, 12: Adder circuit, 3.13: Basso circuit, 4: Impedance element,
5: Current conversion circuit. Agent Patent Attorney Tadashi Sugiura ChitL%selffe, Parable Figure 1 Figure 2 Pigeon 1 Floor 1 Kanfu'ri Figure 2 Figure 8 C Branch 1i Road Figure 3 Figure 4 Figure 7 Figure 9 figure

Claims (2)

[Claims] (1) A first input terminal and a second input terminal that is grounded in terms of AC, a signal addition point connected to the first input terminal, and the first input terminal and the second input terminal. The input signal supplied to the impedance element is supplied to both ends of the impedance element via a voltage follower circuit, and the current flowing through the impedance element is converted into an output current at a predetermined ratio, and the output current is returned to the signal addition point. An impedance conversion circuit comprising: a current conversion circuit that performs a current conversion circuit; (2) a first input terminal and a second input terminal;
a signal addition point connected to each of the input terminal and the second input terminal; and the input signal supplied to the first input terminal and the second input terminal is supplied to both ends thereof via a voltage follower circuit. and a current conversion circuit that converts the current flowing through the impedance element into an output current at a predetermined ratio and feeds back the output current to each of the signal addition points. circuit.