JPH02237212A - Variable reactance circuit - Google Patents

Abstract

PURPOSE:To vary reactance for a wide range from a negative prescribed place to a positive prescribed place by providing first and second amplifier circuits which respectively operate as positive equivalent reactance and negative equivalent reactance. CONSTITUTION:The first amplifier circuit 1 has transistors 4 and 5, a current mirror circuit 9, and a capacitor 10 connected between the collector and the base of the transistor 4, and it shows positive equivalent reactance. The second amplifier circuit 2 has transistors 12 and 13, a current mirror circuit 17 and a capacitor 18 connected between the collector of the transistor 12 and the base of the transistor 13, and it shows negative equivalent reactance. Thus, equivalent reactance viewed from an output terminal 3 can be changed from the negative prescribed place to the positive prescribed place by respectively changing a current flowing in variable current sources 6 and 14.

Description

[Detailed description of the invention] (A) Technical field The present invention relates to a variable reactance circuit, and in particular generates an equivalent reactance that changes from a predetermined negative value to a predetermined positive value based on basic reactance elements such as capacitors and coils. This relates to a variable reactance circuit that can

(Text) Background of the technology Capacitive reactance elements such as capacitors and inductive reactance elements such as coils are obstacles to the use of ICs (integrated circuits), which have been popular in recent years. Attempts are being made to generate Therefore, small-capacity capacitors are still being integrated into ICs, and equivalent inductive reactances are also being integrated into ICs by using gyrators and the like. However, all of them are either fixed or variable in the positive reactance range, and there is still no one that can vary the reactance over a wide range from a negative predetermined value to a positive predetermined value. There wasn't.

(c) Main points of the invention The present invention has been made in view of the above-mentioned points, and includes connecting a reactance element between the base and collector of either one of the first and second transistors that are differentially connected. a first amplifier circuit that exhibits a positive equivalent reactance by controlling the operating currents of the first and second transistors, and a third and fourth transistor that are differentially connected.
The reactance element is connected between the base of one of the transistors and the collector of the other transistor, and the operating currents of the third and fourth transistors are controlled so as to exhibit a negative equivalent reactance. a second amplifier circuit, a current mirror circuit whose input terminal is connected to the collector of the one transistor of the second amplifier circuit, and whose output terminal is connected to the collector of the one transistor of the first amplifier circuit; and an output terminal commonly connected to the input terminal of the second amplifier circuit, and by controlling the operating currents of the first and second transistors and the operating currents of the third and fourth transistors, respectively, It is characterized in that the equivalent reactance seen from the terminal changes from a predetermined negative value to a predetermined positive value.

(2) Embodiment FIG. 1 shows a diagram of the principle of the present invention, in which (1) is a first amplifier circuit that operates as a positive equivalent reactance; (2)
is a second amplifier circuit that operates as a negative equivalent reactance,
and (3) are the first and second amplifier circuits (1) and (
The output terminals of 2) are commonly connected output terminals. Thus, the first amplifier circuit (1) includes first and second transistors (4) and (5) whose emitters are commonly connected;
a first to fourth variable current source (6) connected to a common emitter of the first and second transistors (4) and (5);
4) and (5>) and a first current mirror circuit (9) consisting of a first diode (7) and a third transistor (8) connected to the collector of the first transistor (4) and the collector-base of the first transistor (4). and a first resistor (11) connected between the bases of the first and second transistors 4) and (5), and the second amplifier circuit (2). ) comprises fourth and fifth transistors (12) and (13) whose emitters are commonly connected, and a second variable current source connected to the common emitters of the fourth and fifth transistors (12) and (13). (14); a second current mirror circuit (17) comprising a second diode (15) and a sixth transistor <16) connected to the collectors of the fourth and fifth transistors (12) and (13);
, a second capacitor 8〉 connected between the collector of the fourth transistor (12) and the base of the fifth transistor (13〉), and the fourth and fifth transistors (
12) and (13), the second resistor (
19).

Now, the current flowing through the first variable current source (6) is
Variable current source (zero current flowing through 14〉, output terminal <s)
(7) If WEE is 00 and the current flowing through the first capacitor (10) is iI, the voltage e0 and current i are:
There is a phase difference of 90 degrees, and the current i, whose phase is shifted by 90 degrees with respect to the voltage e0, is connected to the first capacitor (1
0) to the first resistor (11). At that time, the base voltage el of the first transistor (4) is e4 = R-1
+ ・・・・・・・・・・・・(
1) (where R is the resistance value of the first resistor (11)), and the current i, flowing through the first capacitor (10) is as follows. Also, the current i flowing into the output terminal (3) is: i2=e,・gm+i,...
・・・・・・・・・(3) (where, gm is mutual conductance), and the collector current i, (=e1・gm) of the first transistor (4) flows to the first capacitor (1o) If the current is sufficiently larger than the current i, then i2=e,・gm...group・(3'). Note that the phase of the collector current is of the first transistor (4) is equal to the phase of the current 11 flowing through the first capacitor (1o).
, (2) and (3'), it can be considered that the current i, which flows into the output terminal (3), is a capacitor of R-C-gm. For example, the value of the first resistor (11) is IKΩ, the value of the first capacitor (10) is 10, F. The mutual conance is as large as 200,F, and such a large actance can be created within the IC.

Further, mutual conductance is expressed by the following equation.

When viewed from the output terminal 3), assuming an equivalent conversion to a series circuit consisting of the first resistor (20) and the capacitor (21) with a capacitance reactance of R-c-gm, the im-th The circuit has an equivalent capacitance reactor (1. is the current flowing to the first variable current source (6)), therefore, the current I. flowing to the first variable current source (6). and the equivalent capacitance reactance exhibit a proportional relationship, and by changing the current I, it is possible to generate an equivalent capacitance reactance that changes from zero to a predetermined positive value.

Next, if the current flowing through the first variable current source (6) is zero, the current flowing through the second variable current source (14) is , and the current flowing through the second capacitor (18) is i4, then the fifth transistor The base voltage es of (13) is ex = R-f.
− − − (6) (However, R
is the resistance value of the second resistor (19)), and the phase of the current i4 flowing through the second capacitor (18) and the phase of the collector current i6 of the transistor (12>) is the phase of the current i4 flowing through the second capacitor (18). Therefore, from equations (7) and (8'), this becomes the first when viewed from the output terminal (3). Also, the current i6 at the output terminal (3) is i5 =-e,・gm+i4・
......(8) (where gm is mutual conductance), and the collector current i6 (=-es・gm) of the fourth transistor (12) is the same as that of the second capacitor (1
8) If the current flowing through i4 is sufficiently larger than i4, then i6-103 and gm=-R work i4●gm (8').

Incidentally, as is clear from the equation (8'), it shows that the fourth torque is equivalently converted into a series circuit consisting of a capacitor of -R-C-gm.

Also, since the mutual conductance is expressed by the following equation as in Equation (5), by changing the current I2 flowing through the second variable current source (14), the equivalent capacitance reactance that changes from zero to a predetermined negative value can be expressed as follows. It can be generated.

Therefore, the first and second amplifier circuits <1) and (2)
By connecting as shown in the figure and varying the current and I flowing through the first and second variable current sources (6) and (14), the equivalent reactance seen from the output terminal (3) can be set to a negative predetermined value. It is possible to provide a variable reactance circuit that can change the reactance value from a positive predetermined value to a predetermined positive value. In FIG. 1, the case where the first and second variable current sources (6) and (14) are independently controlled has been described, but the first and second variable current sources (6)
) and (14) are configured with a pair of transistors whose emitters are commonly connected, and by applying a differential control signal to the bases of the pair of transistors, the first and second amplifier circuits (6) and (14) are constructed. ) can be commonly controlled. In that case, the positive equivalent reactance and the negative equivalent reactance change according to the differential control signal, and a mixed equivalent reactance is generated at the output terminal (3>).

FIG. 3 shows an embodiment of the present invention based on the principle diagram of FIG.
Transistors (22) and (23) and an output terminal (24)
) and the base of the seventh transistor (22); and a third resistor (25) connected between the bases of the seventh and eighth transistors (22) and (23). 26) and the seventh and eighth transistors (
a constant current circuit (27) connected to the common emitters of 22) and (23); and 9th and 10th transistors (28> and (29>) whose common emitters are connected to the collectors of the seventh transistor (22). and an eleventh transistor whose common emitter is connected to the collector of the eighth transistor (23).
and a twelfth transistor (30) and (31), and a third
A third current mirror circuit (34) includes a diode (32) and a thirteenth transistor (33), and the ninth to twelfth transistors (28) to (31)
) so that a differential control signal is applied to the bases of the two.

Now, if a positive control voltage that is sufficiently larger than the second control terminal (36) is applied to the first control terminal (35), the ninth and twelfth transistors (28) and (31) are turned on. , the tenth and eleventh transistors (29) and (3
0) is turned off, and the circuit in FIG. 3 has the same configuration as the first amplifier circuit (1) in FIG. Therefore, the equivalent reactance seen from the -12-output terminal (24) is the (4th)
) will be the value according to the formula.

One fan 5, the second control terminal (36) has the first control terminal (35)
If a positive control voltage sufficiently larger than is applied, the ninth and twelfth transistors (28) and (31)
is off, the 10th and 11th transistors (29) and (
30) is turned on, and the circuit of FIG. 3 has the same configuration as the second amplifier circuit (2) of FIG. 1. Therefore, the output terminal (
The equivalent reactance seen from 24) is a value according to equation (9).

If equal control voltages are applied to the first and second control terminals (35) and (36), the positive equivalent reactance and the negative equivalent reactance are canceled and the output terminal (24) When the observed equivalent reactance becomes zero and the control voltages applied to the first and second control terminals (35) and (36) are in the middle of each of the above states,
The positive and negative equivalent reactances according to the conduction of the 9th to 12th transistors (28) to (31) are output terminals (24).
occurs in

FIG. 4 shows another embodiment of the present invention, in which a first current source transistor (37
) are connected to the fourteenth and fifteenth transistors (38>
and (39〉) and a second variable current source to the common emitter.
The 16th and 17th transistors 41) and (42) to which the current source transistor (40) is connected, and the output terminal (
43) and the base of the fourteenth transistor (38); a fourth capacitor (44) connected between the common base of the fourteenth and seventeenth transistors (38) and (42) and the fifteenth and sixteenth transistor; Transistors (39> and (4)
A fourth resistor (45) connected between the common base of 1)
, the 4th die (46) and the 18th transistor (4
7), and a fourth current mirror circuit (48) consisting of the first and second current source transistors (37).
) and (40), a predetermined equivalent reactance is generated at the output terminal (43).

Now, a predetermined control signal is applied to the base of the first current source transistor (37), and the second current source transistor (40)
If no control signal is applied to the base of The configuration is the same, and when viewed from the output terminal (43), the (4th)
) gives a positive equivalent reactance according to the equation. Then, depending on the magnitude of the control signal applied to the base of the first current source transistor <37), its collector current
1 changes, a variable reactance circuit is obtained that generates an equivalent reactance from zero to a positive predetermined value.

Furthermore, if a predetermined control signal is applied to the base of the second current source transistor (40) without applying a control signal to the base of the first current source transistor (37), then the second current source transistor (40) The collector current flows through the circuit in Figure 4, and the circuit in Figure 4 has exactly the same configuration as the second amplifier circuit (2) in Figure 1.
) The equivalent reactance is obtained according to the formula. Since the collector current I2 changes depending on the magnitude of the control signal applied to the base of the second current source transistor (40), a variable reactance that generates an equivalent reactance from zero to a predetermined negative value is used. A circuit is obtained.

Note that the first and second current source transistors (37> and (4)
This can also be done by applying a differential control signal to the base of 0), and the operation in that case can be considered in the same way as in the case of FIG.

The circuit shown in FIG. 4 can significantly reduce the number of elements compared to the circuit shown in FIG. That is, the capacitor, current mirror circuit, and resistor can each be halved. In particular, since capacitors lead to an increase in chip area when integrated into ICs, this is a great advantage. Furthermore, although the current mirror circuit may generate an offset current, this can also be reduced by reducing the number of current mirror circuits. Furthermore, the fourth
In the circuit shown in the figure, even if a large amplitude signal is applied to the output terminal (43), the two amplifier circuits are not saturated and can exhibit reactance characteristics. That is, the output terminal (
43) When a large amplitude signal is applied to the fourth capacitor (
44) and the fourth resistor (45) is the voltage divided by the first resistor (44) and the fourth resistor (45).
The divided voltage is applied to the bases of the fourth and seventeenth transistors (38) and (42), but since the value of the fourth resistor (45) is very small, the divided voltage has a sufficiently low level. Therefore, the two amplifier circuits can always be used in the linear region and exhibit stable actance characteristics.

FIG. 5 shows another embodiment of the present invention, in which the first and second capacitors (10) and (18) of FIG. 1 are replaced by first and second coils (49) and (50). ) to generate an equivalent inductive reactance at the output terminal (51). The circuit operation is similar to that shown in Fig. 1, and the output terminal (51) has the first and second coils (4
9> and (50) inductive reactance L. A positive and negative equivalent inductive reactance of a predetermined multiple of and L is generated.

FIG. 6 shows an example of the case where the variable reactance circuit according to the present invention is used in an oscillation circuit, where (52) is a pair of differentially connected transistors (53) and (54).
(55) is an oscillation element such as a crystal resonator, and (56) is the variable reactance circuit shown in FIG. 1, FIG. 3, or FIG. 4 according to the present invention.

However, if the circuit configuration is as shown in Fig. 6, the oscillation element (
55), a variable reactance circuit (
56> equivalent reactances are connected in parallel, and the parallel resonance frequency changes depending on the value of the equivalent reactance of the variable reactance circuit (56). Now, the 7th
As shown in the figure, if the parallel resonance frequency unique to the oscillation element (55) when the variable reactance circuit (56) is not connected is r1, then the equivalent reactance of the variable reactance circuit (56) is a predetermined positive value from zero. As the reactance changes from zero to f2, the parallel resonance frequency moves in the direction of arrow A to f2, and as the reactance changes from zero to a negative predetermined value, the parallel resonance frequency moves in the direction of arrow B to r. Therefore,
For example, in FIG. 1, the first or second variable current source (
If the current I or I2 in 6) or (14) is changed, the parallel resonance frequency of the oscillation element (55) is substantially changed, and the oscillation frequency of the oscillation circuit is changed.

(e) Effects As described above, the present invention has the great feature that it is possible to easily create positive and negative equivalent reactances that are a predetermined times the value of the basic reactance element using a circuit that can be integrated into an IC. In particular, the equivalent reactance can be varied over a wide range from a negative predetermined value to a positive predetermined value depending on the control signal, so it can be used for various purposes. Furthermore, compared to the embodiment shown in Fig. 1, the circuit configuration of the embodiment shown in Fig. 4 is such that capacitors, resistors, current sources, etc., which are basic reactance elements, are shared by the first and second amplifier circuits. It has the advantage of being easier to work with. Furthermore, as shown in FIG. 6, if the variable reactance circuit according to the present invention is used in an oscillation circuit, the oscillation frequency can be adjusted around the unique frequency of an oscillation element such as a crystal resonator with a stable oscillation frequency, for example, in a PLL.
Since the oscillation frequency of the oscillation circuit can be varied up and down using the signal from the phase comparator of the circuit as a control signal, it has the advantage of providing a vCO (voltage controlled oscillator) with a stable free-run frequency. .

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the principle of the invention, Fig. 2 is a partial equivalent circuit diagram thereof, Fig. 3 is a circuit diagram showing an embodiment of the invention, and Fig. 4 shows another embodiment of the invention. A circuit diagram, FIG. 5 is a circuit diagram showing another embodiment of the present invention, and FIG. 6 is a circuit diagram showing an oscillation circuit using the variable reactance circuit according to the present invention.
and FIG. 7 are characteristic diagrams for explaining the same. Explanation of main drawing numbers (1)...First amplifier circuit, (2)...Second amplifier circuit, (3)...Output terminal, (4)(5)(12)<
13)...Transistor, (6)(14)...Variable current source, (10)(18)...Capacitor, (
11) (19)...Resistance.

Claims (1)

[Claims] (1) By connecting a reactance element between the base and collector of one of the first and second transistors that are differentially connected, and controlling the operating current of the first and second transistors, positive equivalence can be achieved. The reactance element is connected between a first amplifier circuit configured to exhibit reactance and a base of one of differentially connected third and fourth transistors and a collector of the other transistor. a second amplifier circuit configured to exhibit a negative equivalent reactance by controlling the operating currents of the third and fourth transistors; an input terminal connected to the collector of the one transistor of the second amplifier circuit; a current mirror circuit connected to the collector of the one transistor of the first amplifier circuit; and an output terminal commonly connected to the input terminals of the first and second amplifier circuits; The variable device is characterized in that the equivalent reactance seen from the input terminal is changed from a predetermined negative value to a predetermined positive value by controlling the operating current and the operating currents of the third and fourth transistors, respectively. reactance circuit.