JP2008278159A - Variable capacitance circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable capacitance circuit which uses a negative impedance conversion circuit 3 for a correction means for linearizing relationship of a change in reverse control voltage applied to a variable capacitance diode 2 versus a change in the capacitance of the variable capacitance circuit and eliminates the need of using a complicated correction means without narrowing a capacitance change range. <P>SOLUTION: The variable capacitance circuit is equipped with: the variable capacitance diode 2 connected between a non-grounding side input terminal 1a and a grounding side input terminal 1b and supplied with the variable control voltage of a controllable voltage forming apparatus 6; and the negative impedance conversion circuit 3 provided with an input end, an output end and a grounding end, whose input end is connected to the non-grounding side input terminal 1a and output end is connected through a capacitor 5 to the grounding side input terminal 1b. The capacitance of the capacitor 5 is selected to be a value almost equal to a distribution capacitance formed between the non-grounding side input terminal 1a and the grounding side input terminal 1b, and the capacitance of the variable capacitance diode 2 is logarithmically changed as the variable control voltage is linearly changed by the adjustment of the controllable voltage forming apparatus 6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable capacitance circuit, and in particular, the control voltage vs. capacitance change characteristic exhibited by a variable capacitance diode is such that the capacitance changes logarithmically with respect to a linear change in control voltage by using a negative impedance conversion circuit. The present invention relates to a variable capacitance circuit capable of correcting or correcting a capacitance so as to change linearly with respect to a linear change in control voltage.

  Capacitance change characteristics in variable capacitance diodes vary in degree depending on the type of variable capacitance diode, but in general, in a range where the applied reverse control voltage is relatively low, the relationship between the reverse control voltage and the capacitance is obtained. The logarithmic change of the capacitance with respect to the linear change of the reverse control voltage is a relatively close linearity with a constant slope, while the reverse control voltage and the capacitance are in a range where the applied reverse control voltage is relatively high. When the relationship is obtained, the logarithmic change of the capacitance with respect to the linear change of the reverse control voltage has a characteristic that the slope thereof gradually becomes gradually, and when the reverse control voltage reaches the highest range, it almost approaches the horizontal state.

  By the way, when a variable capacitance diode is used in the LC tuning circuit and the capacitance change of the variable capacitance diode is used, it is preferable that the capacitance changes logarithmically with respect to the linear change of the reverse control voltage, and the active filter has a variable capacitance. When a diode is used and the capacitance change of the variable capacitance diode is used, it is preferable that the capacitance linearly changes with respect to the linear change of the reverse control voltage. This is because in the LC tuning circuit, the change in the LC resonance frequency is inversely proportional to the square root of the capacitance value of the variable capacitance diode, whereas in the active filter, the change in the resonance frequency is simply variable. This is because it is inversely proportional to the change in the capacitance value of the capacitance diode.

  Regardless of whether the variable capacitance diode is used as the variable capacitance element of the LC tuning circuit or the variable capacitance element of the active filter, the variable capacitance diode is adapted to the linear change of the reverse control voltage applied to the variable capacitance diode. It is necessary to correct so that the capacitance change characteristic becomes linear with respect to the linear change of the reverse control voltage applied to the variable capacitance diode.

  Here, when a variable capacitance diode is used in the LC tuning circuit, a simple linearization means conventionally used for the capacitance change of the variable capacitance diode is a correction means for connecting a correction capacitor in series with the variable capacitance diode. . If this correction means is used, the total capacitance value of the variable capacitance diode and the correction capacitor is hardly affected by the correction capacitor on the minimum capacitance value side of the variable capacitance diode, and the total capacitance value changes to a linear change in the reverse control voltage. In contrast, when the capacitance value of the variable capacitance diode increases, the total capacitance value is affected by the correction capacitor, and as the capacitance value increases, the total capacitance value decreases. The rate of the horizontal bending of the capacitance change in the region where the capacitance value of the variable capacitance diode is large becomes gradual, and as a result, the total capacitance value approaches a linear change.

Further, when a variable capacitance diode is used for the active filter, even if correction means for connecting a correction capacitor in series with the variable capacitance diode is used, it is possible to prevent the linear change of the reverse control voltage between the variable capacitance diode and the correction capacitor. Since the correction means makes the logarithmic change of the total capacitance value a substantially straight line, it cannot be used for a linear change of the total capacitance value of the variable capacitance diode and the correction capacitor with respect to the linear change of the reverse control voltage. . For this reason, here, the reverse control voltage applied to the variable capacitance diode is converted into a nonlinear reverse control voltage by passing through a nonlinear circuit using a semiconductor element, and this nonlinear reverse control voltage is applied to the variable capacitance diode to obtain its capacitance. By controlling the value, correction means for linearizing the capacitance change characteristic of the variable capacitance diode with respect to the input reverse control voltage is used.
No patent literature to use

  In an LC tuning circuit using a known variable capacitance diode, when a reverse control voltage is applied to the variable capacitance diode, a correction means for logarithmically changing the capacitance value of the variable capacitance diode with respect to a linear change of the reverse control voltage As a correction means, a correction capacitor is used in which a correction capacitor is connected in series with a variable capacitance diode. When this correction means is used, the change region of the total capacitance value is the change region when the correction capacitor is not used. It will be narrower than that.

  Further, in an active filter using a variable capacitance diode, as a correction means for linearly changing the capacitance value of the variable capacitance diode with respect to a linear change of the reverse control voltage when a reverse control voltage is applied to the variable capacitance diode. Converts a reverse control voltage applied to a variable capacitance diode into a non-linear reverse control voltage by passing through a non-linear circuit using a semiconductor element, and applies this non-linear reverse control voltage to the variable capacitance diode to control its capacitance value. Therefore, the correction means for linearizing the capacitance change characteristic of the variable capacitance diode with respect to the input reverse control voltage is used. However, the nonlinear circuit using this semiconductor changes the characteristics of the semiconductor cutoff region to the conduction region. It is intended to correct using the characteristics, and it is necessary to construct a nonlinear circuit that takes into account the temperature characteristics, Road construction had to become naturally more complex.

  The present invention has been made in view of such a technical background, and its object is to provide a negative impedance conversion circuit as a correction means for linearizing the relationship between applied reverse control voltage change and capacitance change in a variable capacitance diode. And a variable capacitance circuit that does not require a complicated correction means without narrowing the capacitance change range.

  To achieve the above object, a variable capacitance circuit according to the present invention is connected between a non-ground side input terminal and a ground side input terminal, and is supplied with a variable control voltage output from a controllable voltage generator. And a negative impedance conversion circuit having an input end, an output end, and a ground end, the input end being connected to the non-ground side input terminal, and the output end being connected to the ground side input terminal via a capacitive element. A negative impedance conversion circuit, and the capacitance value of the capacitive element is selected to be substantially equal to the distributed capacitance value formed between the non-ground side input terminal and the ground side input terminal, thereby forming a controllable voltage First configuration means formed so that the capacitance value of the variable capacitance diode changes logarithmically as the variable control voltage output from the controllable voltage forming device is linearly changed by adjusting the device. To.

  In order to achieve the above object, the variable capacitance circuit according to the present invention is connected between the non-ground side input terminal and the ground side input terminal and supplied with the first variable control voltage output from the controllable voltage forming device. Negative impedance conversion circuit having a first variable capacitance diode, an input end, an output end, and a ground end, the input end being connected to the non-ground side input terminal, and the output end being a controllable voltage forming device And a negative impedance conversion circuit connected to the ground-side input terminal via a second variable capacitance diode capacitive element supplied with a second variable control voltage output from the first variable control voltage, The variable control voltage of 2 is configured to increase or decrease in the opposite direction by adjustment of the controllable voltage forming device, and to change the capacitance values of the first and second variable control voltages in the opposite directions. Control voltage The total capacitance value of the first and second variable capacitance diodes is linearly changed in the positive and negative capacitance regions as the first and second variable control voltages output from the generator are linearly changed. Second configuration means is provided.

  Furthermore, in order to achieve the above object, the variable capacitance circuit according to the present invention has a fixed capacitance element in parallel with the first variable capacitance diode between the non-ground side input terminal and the ground side input terminal in the second configuration. As the first and second variable control voltages are linearly changed, the total capacitance value of the first and second variable capacitance diodes is linear only in the positive capacitance region. A third component means is provided which is chosen to be a variable value.

  As described above in detail, the variable capacitance circuit according to the present invention is configured by connecting one or two variable capacitance diodes, a controllable voltage forming device, and a negative impedance conversion circuit between a pair of input terminals. The capacitance formed between the pair of input terminals by adjustment of the control voltage forming device is substantially linear when recorded on a semi-log scale graph, or substantially when recorded on a bilinear scale graph. The correction is made to be linear, and can be realized without narrowing the capacitance change range and without using a complicated circuit configuration for the correction means. It is suitable for use when adjusting the cutoff frequency of the active filter.

  Here, the configuration principle of the variable capacitance circuit according to the present invention will be described.

  First, the first of the configuration principles of the present invention is that the relationship between the linear change of the reverse control voltage applied to the variable capacitance diode and the logarithmic change of the capacitance of the variable capacitance diode due to the application of the reverse control voltage is substantially linear. The state is corrected so as to be linear.

  Here, FIGS. 3A and 3B are characteristic curves recorded on a semi-log scale graph showing the change state of the capacitance of the variable capacitance diode corresponding to the change state of the reverse control voltage applied to the variable capacitance diode. The horizontal axis direction represents the reverse control voltage graduated at equal voltage intervals, the vertical axis direction represents the capacitance of the variable capacitance diode graduated in logarithmic capacity, and the real curve (a) represents the normal reverse control voltage change. This is a change characteristic indicating a change in capacitance, and a dotted line (b) is a change characteristic obtained by correcting a change in capacitance with respect to a reverse control voltage change according to the present invention.

  As shown by the solid curve (a) in FIG. 3, normally, when the reverse control voltage applied to the variable capacitance diode is sequentially increased from the minimum voltage value, the reverse control voltage of the region near the minimum voltage value is increased. The change characteristic of the capacitance of the variable capacitance diode with respect to the increase decreases along a straight line with a constant slope, but the capacitance of the variable capacitance diode with respect to the increase of the reverse control voltage as the maximum voltage value is approached from the intermediate voltage value. The slope indicating the decrease of the change characteristic gradually becomes a gentle slope value from the constant slope value, and finally the slope becomes a curve that approaches the horizontal.

  In this case, the fact that the slope of the change characteristic of the capacitance of the variable capacitance diode has approached a horizontal state indicates that the capacitance of the variable capacitance circuit at that time has approached the distributed capacitance of the input circuit portion including the variable capacitance diode. Therefore, even if the reverse control voltage is changed, the change rate of the capacitance is extremely small. Therefore, the variable capacitance circuit according to the present invention performs correction so as to cancel this distributed capacitance by using a negative impedance conversion circuit, so that the variable capacitance circuit is displayed on the semilogarithmic scale graph as shown by a dotted line (b) in FIG. A substantially linear characteristic curve is obtained.

  FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention that can realize a substantially linear characteristic curve by performing correction so as to cancel out such a distributed capacity, and a part of the configuration part is shown in FIG. It is shown by a circuit block.

  In FIG. 1, 1a is a non-ground side input terminal, 1b is a ground side input terminal, 2 is a variable capacitance diode, 3 is a negative impedance conversion circuit (NCC), 4 is an input coupling capacity, 5 is a load capacity, and 6 is possible. A control voltage forming device 7 is a buffer resistor.

The variable capacitance diode 2 has a cathode connected to the non-ground side input terminal 1a through the input coupling capacitor 4 and an anode connected to the non-ground side input terminal 1b, respectively, and a series circuit of the controllable voltage generator 6 and the buffer resistor 7 is also provided. The variable capacitance diode 2 is connected in parallel. The negative impedance conversion circuit 3 has an input end, an output end, and a ground end. The input end is connected to the non-ground side input terminal 1a through the input coupling capacitor 4, and the output end is connected to the ground end through the load capacitor 5. Connected to the ground side input terminal 1b. In this case, the load capacitance 5 has a capacitance value substantially equal to the distributed capacitance value C ₀ (6 pF in the case of the characteristic curve shown in FIG. 2) formed between the non-ground side input terminal 1a and the ground side input terminal 1b. Have chosen so.

With such a configuration, the capacitance value of the load capacitor 5 connected to the output terminal of the negative impedance conversion circuit 3 is set to the distributed capacitance value C ₀ formed between the non-ground side input terminal 1a and the ground side input terminal 1b. Therefore, the negative capacitance value when the negative impedance conversion circuit 3 side is viewed from the output terminal of the negative impedance conversion circuit 3 is −C ₀ , and the non-ground side input terminal 1a and the ground side input terminal are selected. The distributed capacitance value C ₀ formed between 1b is canceled out. For this reason, the total capacitance value including the variable capacitance diode 2 formed between the non-ground side input terminal 1 a and the ground side input terminal 1 b is reversely controlled supplied to the variable capacitance diode 2 by adjustment of the controllable voltage forming device 6. When the voltage is increased linearly and sequentially, the total capacitance value is hardly affected by the negative capacitance value −C _{0 in} the region close to the minimum voltage value, and the decrease in the total capacitance value is extremely small. As the voltage value region is approached, the total capacitance value is affected by the negative capacitance value −C ₀ , and the decrease in the total capacitance value sequentially increases. As a result, the total capacitance value is represented by a dotted line (b) in FIG. As shown, the change characteristic is almost linear.

  Next, the second configuration principle of the present invention is that the first and second linear changes of the reverse control voltages applied to the first and second variable capacitance diodes and the application of these reverse control voltages, respectively. So that the relationship of the characteristic curve representing the logarithmic change in the opposite direction of each capacitance of the variable capacitance diode of FIG. This is a characteristic curve on the other side rotated by 180 ° and corrected so as to show a total capacity change characteristic extending in a straight line direction in the positive and negative capacity value direction as a whole through the total capacity value zero point. As an example in this configuration principle, the position of the total capacitance value zero is set to a point where the reverse control voltages to the first and second variable capacitance diodes are 6V, respectively.

Here, FIGS. 4 (a ₁ ), (a ₂ ), and (b) show the first and second variable variables corresponding to the change states of the reverse control voltages applied to the first and second variable capacitance diodes, respectively. A characteristic curve in which the capacitance change state of the capacitance diode is recorded on both linear scale graphs. The horizontal axis direction is a reverse control voltage graduated at equal voltage intervals, and the vertical axis direction is equal capacitance intervals. The scaled total capacitances of the first and second variable capacitance diodes are respectively shown, and the real curve (a ₁ ) is a characteristic curve indicating the change in capacitance with respect to the normal reverse control voltage change of the first variable capacitance diode. a ₂ ) is a characteristic curve showing the capacitance change with respect to the normal reverse control voltage change of the second variable capacitance diode, and the dotted solid line (b) is a linear change of the total capacitance corresponding to the reverse control voltage change in both directions according to the present invention. With a characteristic curve corrected to That.

As shown in the respective real curves (a ₁ ) and (a ₂ ) of FIG. 4, when the reverse control voltages applied to the first and second variable capacitance diodes are sequentially increased from the minimum voltage value, the reverse control is performed. In the region close to the minimum voltage value, the characteristic curve indicating the capacitance change of the first and second variable capacitance diodes with increasing reverse control voltage decreases linearly, but as the intermediate voltage value approaches the maximum voltage value, The decreasing slope of the characteristic curve indicating the capacitance change of the first and second variable capacitance diodes with respect to the increase of the reverse control voltage gradually becomes gradual, and finally the characteristic curve approaches a horizontal curve. Therefore, the characteristic curve corrected by the present invention is a characteristic that shows a linear capacitance change by combining the same shape characteristic curves indicating the capacitance changes of the first and second variable capacitance diodes using a negative impedance conversion circuit. Curves, that is, substantially straight characteristic curves are obtained on both linear scale graphs as shown in FIG. 4B.

  FIG. 2 is a circuit configuration diagram according to an embodiment of the present invention capable of realizing a characteristic curve subjected to such correction, and a part of the configuration is shown as a circuit block.

  In FIG. 2, 11a is a non-ground side input terminal, 11b is a ground side input terminal, 12 is a first variable capacitance diode, 13 is a second variable capacitance diode, 14 is a negative impedance conversion circuit (NCC), and 15 is Input coupling capacitors, 16a and 16b are controllable voltage generating devices, 17a and 17b are buffer resistors, 18 is an output coupling capacitor, and 19 is a bypass capacitor.

  The first variable capacitance diode 12 has a cathode connected to the non-ground side input terminal 11 a through the input coupling capacitor 15, an anode connected to the non-ground side input terminal 11 b, and in parallel to the first variable capacitance diode 12. A series circuit of one controllable voltage forming device 16a and a buffer resistor 17a is connected. The second variable capacitance diode 13 has a cathode connected to the output terminal of the negative impedance conversion circuit 14 through the output coupling capacitor 18, an anode connected to the ground side input terminal 11b through the bypass capacitor 19, and one controllable one. It is connected to a connection point between the voltage forming device 16a and the buffer resistor 17a. A series circuit of the other controllable voltage generating device 16b and the buffer resistor 17b is connected between the cathode of the second variable capacitance diode 13 and the ground side input terminal 11b.

  In this case, the first variable-capacitance diode 12 and the second variable-capacitance diode 13 are changed when the capacitance of the first variable-capacitance diode 12 is increased or decreased by adjustment of one controllable voltage generator 16a. The connection polarity of the first and second variable capacitance diodes 12 and 13 is selected so that the capacitance of the two variable capacitance diodes 13 is differentially decreased or increased, and the first and second variable capacitance diodes 12 and 12 are selected. The connection states of one controllable voltage forming device 16a and the other controllable voltage forming device 16b connected to each other are set.

  With this configuration, the first variable capacitance diode 12 is connected to the input end side of the negative impedance conversion circuit 3, and the second variable capacitance diode 13 is connected to the output end side of the negative impedance conversion circuit 3. By adjusting one of the controllable voltage forming devices 16a, the capacitance change direction of the first variable capacitance diode 12 and the capacitance change direction of the second variable capacitance diode 13 are opposite to each other. The capacitance of the variable capacitance diode 13 becomes a negative capacitance when viewed from the input terminal of the negative impedance conversion circuit 3, and is added to the capacitance of the first variable capacitance diode 12. Therefore, the non-ground side input terminal 11a and the ground The total capacitance including the first and second variable capacitance diodes 12 and 13 formed between the side input terminals 11b is substantially linear as shown by the dotted line (b) in FIG. It becomes curve.

Then, as can be seen from the solid curves (a ₁ ), (a ₂ ) and the dotted line (b) shown in the graph of FIG. 4, the first variable capacitor is adjusted by adjusting one controllable voltage forming device 16 a. The capacity when the reverse control voltage applied to the diode 12 is about 2V is 400 pF (see point P), and the capacity when the reverse control voltage applied to the second variable capacitance diode 13 is about 10V. Assuming −100 pF (see Q point), the total capacity of the capacitance at point P (400 pF) and the capacitance at point Q (−100 pF) is 300 pF (see R point). Similarly, by adjusting one controllable voltage generator 16a, the reverse control voltage applied to the first variable capacitance diode 12 and the reverse control voltage applied to the second variable capacitance diode 13 are opposite to each other. Even when it is changed to, their total capacity moves on the straight line shown by the dotted line (b).

  By the way, the variable capacitance circuit shown in FIG. 2 has a region showing a negative capacitance as shown in the lower half of the dotted line (b) in FIG. It is easier to use if there is no area showing capacity.

  FIG. 5 is a circuit configuration diagram showing an embodiment of the present invention in which a variable capacitance circuit without such a region showing negative capacitance is realized. Similarly, some of the components are shown as circuit blocks. It is what.

  In FIG. 5, reference numeral 20 denotes an additional capacitor connected in parallel to the first variable capacitance diode 12, and other components that are the same as those shown in FIG. Is omitted.

  As shown in FIG. 5, the variable capacitance circuit is obtained by connecting an additional capacitor 20 in parallel to the first variable capacitance diode 12, and the negative capacitance in the dotted line (b) of FIG. 4 depends on the capacitance of the additional capacitor 20. The area is substantially eliminated. That is, the straight line shown in FIG. 4C is obtained by shifting the entire dotted line (b) in the positive capacity direction by the capacity of the additional capacitor 20, and in the example of FIG. Is selected to be about 500 pF. With this configuration, the variable capacitance circuit does not generate a negative capacitance due to the adjustment of the controllable voltage generator 16a, and a variable capacitance circuit that is easy to use can be obtained.

  By the way, the negative impedance conversion circuit used in the variable capacitance circuit as described above is configured differently depending on the frequency band used for the variable capacitance circuit, and the variable capacitance circuit is relatively similar to an active filter or the like. When used in a low frequency signal band, it is preferable to use a negative impedance conversion circuit using an operational amplifier.

FIG. 6 shows an example of the configuration of a negative impedance conversion circuit using an operational amplifier. 21 ₁ is a non-ground side input terminal, 21 ₂ is a ground side input terminal, 22 is an operational amplifier, and 23, 24, and 25 are impedances. It is. The operational amplifier 22 has an impedance 23 connected between the non-inverting input terminal (+) and the output terminal, an impedance 24 connected between the inverting input terminal (−) and the output terminal, and a non-inverting input terminal ( +) Is connected to the non-grounded input terminal 21 ₁ , and an impedance 25 is connected between the inverting input terminal (−), the output terminal, and the grounded input terminal 21 ₂ .

The operation of the negative impedance converter circuit is such that when the input voltage ei is supplied between the input terminals 21 ₁ and 21 ₂ and the input voltage ei is supplied to the non-inverting input terminal (+) of the operational amplifier 22, If the output voltage is eo, the current flowing through the impedance 23 is i, and the impedances of the three impedances 23, 24 and 25 are Z ₁ , Z ₂ and Z ₃ , respectively, the input impedance Zin viewed from the input terminals 21 ₁ and 21 ₂ Is represented by Zin = ei / i. At this time, since there is a relationship of i = (ei−eo) / Z ₁ and ei = eo {Z ₃ / (Z ₂ + Z ₃ )}, the input impedance Zin is
Zin = − {(Z ₁ · Z ₃ ) / Z ₂ } (1)
It becomes.

Here, if the impedances 23 and 24 are selected as resistance elements, the impedances Z ₁ and Z ₂ are resistances R ₁ and R ₂ , the impedance 25 is selected as a capacitance element, and the impedance Z ₃ is a capacitance C ₃ , Since Z ₃ = 1 / sC ₃ (s is a Laplace transformer), the input impedance Zin is
Zin = − {R ₁ / (sC ₃ · R ₂ )} (2)
Thus, a negative capacity {-(C ₃ · R ₂ ) / R ₁ } is formed.

On the other hand, if the impedances 24 and 25 are selected as resistance elements, the impedances Z ₂ and Z ₃ are selected as resistances R ₂ and R ₃ , the impedance 22 is selected as a capacitance element, and the impedance Z ₁ is defined as a capacitance C _1. Impedance Zin is
Zin = − {R ₃ / (sC ₁ · R ₂ )} (3)
Thus, a negative capacity {-(sC ₁ · R ₂ ) / R ₃ } is formed.

In this case, the operation of the operational amplifier 22 is almost the same even if elements connected to the non-inverting input terminal (+) and the inverting input terminal (−), for example, impedances 23 and 24 are connected to the opposite input terminals. It is. Further, as apparent from the previous equations (2) and (3), R ₁ / R ₂ and R ₃ / R ₂ are coefficients, respectively, so that the same type of impedance can be used even if it is a capacitive element. Although it may be an element, it goes without saying that a resistance element is most easily used.

  Next, FIG. 7 is a circuit showing one configuration example of a negative capacitance circuit in which the negative impedance conversion circuit shown in FIG. 6 is combined with a circuit for operating the first and second variable capacitance diodes differentially. It is a block diagram.

  In FIG. 7, reference numeral 26 denotes a coupling capacitor, which has a large capacity showing a low impedance at the operating frequency, 27 is a resistance element, a zero potential maintaining resistor having a high resistance value, The same components as those illustrated in FIGS. 5 and 6 are denoted by the same reference numerals, and description thereof will be omitted.

  The negative capacitance circuit according to the present configuration example performs substantially the same operation as that of the negative capacitance circuit illustrated in FIG. 5, and the first variable capacitance diode 12 and the second variable capacitance diode 13 include: Adjustment of one controllable voltage generator 16a causes the reverse control voltage applied to the first variable capacitance diode 12 and the reverse control voltage applied to the second variable capacitance diode 13 to change in the opposite directions to each other. The total capacity including the capacity of the capacity 20 moves on the line indicated by the straight line shown in FIG.

  On the other hand, when this variable capacitance circuit is used in a relatively high frequency signal band such as an LC tuning circuit, it is preferable to use a negative impedance conversion circuit composed of discrete elements. There is a negative impedance conversion circuit described in Japanese Patent Application Laid-Open No. 2005-303505 presented by the present applicant. The negative impedance conversion circuit described in Japanese Patent Laid-Open No. 2005-303505 includes an amplification stage including a pair of input transistors whose emitters and collectors are commonly connected, and an output transistor connected to the common connection. The positive feedback loop and the negative feedback loop from the collector and emitter of the output transistor to the base of the pair of input transistors are connected.

  The negative impedance conversion circuit having such a configuration can be used up to a somewhat high frequency signal band, but requires at least about 40 dB for the positive feedback loop gain and the negative feedback loop gain of the amplification stage. When the upper limit of the possible frequency signal band is made higher, it is necessary to select the resistance values of the collector load resistance and the emitter load resistance of the output transistor to be small, and as a result, the loop gain of the amplification stage may be insufficient. In such a case, it is necessary to increase the amplification gain by increasing the number of amplification stages, or to increase the amplification gain in the same manner by using an amplification stage composed of a composite transistor connected in Darlington within one chip.

  Next, FIGS. 8 and 9 show a configuration example of a negative capacitance circuit using a negative impedance conversion circuit that satisfies the above-described requirements. The configuration example shown in FIG. 8 is a negative impedance conversion circuit. FIG. 9 shows a configuration example of a negative capacitance circuit using a combination of one variable capacitance diode and the configuration example shown in FIG. 9 includes the first and second variable capacitance diodes in the negative impedance conversion circuit. The example of a structure of the negative capacity circuit used in combination is shown.

As shown in FIG. 8, the negative impedance conversion circuit 28 according to the present configuration example includes an amplification stage including a pair of input transistors 29 ₁ , 29 ₂ and an output transistor 30 having emitters connected in common, a coupling capacitor 31, and feedback. It consists of a positive feedback loop composed of a resistor 33 and a negative feedback loop composed of a coupling capacitor 31, 32 and a feedback resistor 34. Then, the signal supplied to the base of the input transistor 29 _1, the input transistor 29 ₁ is the emitter follower operation performs input transistor 29 ₂ is grounded base operation, the output transistor 30 is grounded emitter operation, the output transistor 30 signal generated in the collector is fed back to the base of the input transistor 29 ₁ through the negative feedback loop, whereas, for the signal supplied to the base of the input transistor 29 _2, input transistors 29 ₂ and the output transistor 30 is grounded emitter operation was carried out, the signal generated in the collector of the output transistor 30 is fed back to the base of the input transistor 29 ₂ via the positive feedback loop, is constituted negative impedance converter circuit 28.

  In this case, the negative capacitance circuit shown in FIG. 8 is different from the negative capacitance circuit 3 shown in FIG. 1 only in the internal configuration of the negative impedance conversion circuit 28. Further, the configuration other than the negative impedance conversion circuit 28 is the same as that of the negative capacitance circuit shown in FIG. For this reason, the same components as those shown in FIG. 1 are denoted by the same reference numerals, description of those components is omitted, and the operation of the negative capacitance circuit shown in FIG. Since the operation of the negative capacitance circuit shown in FIG. 1 is almost the same, the description of the operation of the negative capacitance circuit is also omitted.

As shown in FIG. 9, the negative capacitance circuit 35 according to this configuration example includes an amplification stage including a pair of input Darlington connection composite transistors 36 ₁ and 36 ₂ and an output transistor 37, a coupling capacitor 38, and a feedback resistor 39. And a negative feedback loop composed of a feedback resistor 40 and a coupling capacitor 41. Then, the signal supplied to the base of the input Darlington-connected composite transistor 36 _1, input Darlington-connected composite transistor 36 ₁ is grounded emitter operation, the output transistor 37 performs substantially the emitter follower operation, the output transistor 37 signals generated in the emitter is fed back to the base of the Darlington-connected composite transistor 36 ₁ through the negative feedback loop, whereas, for the signal supplied to the base of the input Darlington-connected composite transistor 36 _2, input Darlington-connected composite transistor 36 ₂ There performed grounded emitter operation and the output transistor 37 is substantially grounded emitter operation, the signal generated in the collector of the output transistor 37 is fed back to the base of the input Darlington-connected composite transistor 36 ₂ via the positive feedback loop, negative impedance The scan conversion circuit 35 is configured.

  In this case, the negative capacitance circuit shown in FIG. 9 is different from the negative capacitance circuit 3 shown in FIG. 5 only in the internal configuration of the negative impedance conversion circuit 35. The configuration other than the negative impedance conversion circuit 35 is the same as that of the negative capacitance circuit 14 shown in FIG. For this reason, the same components as those shown in FIG. 5 are denoted by the same reference numerals, description of those components is omitted, and the operation of the negative capacitance circuit shown in FIG. Since the operation of the negative capacitance circuit shown in FIG. 5 is almost the same, the description of the operation of the negative capacitance circuit is also omitted.

It is a circuit block diagram which shows one embodiment of this invention which can correct | amend so that distribution capacity may be canceled and can implement | achieve a substantially linear characteristic curve. It is a circuit block diagram which shows one embodiment of this invention which can implement | achieve and implement | achieve the characteristic curve extended linearly in the positive / negative capacitance direction by correcting. It is the characteristic curve recorded on the semilogarithmic scale graph which shows the change state of the capacity | capacitance of the variable capacity diode corresponding to the change state of the reverse control voltage applied to a variable capacity diode. It is the characteristic curve which recorded the change state of those capacity | capacitances corresponding to the change state of the reverse control voltage applied to the 1st and 2nd variable capacitance diode on both linear scale graphs. It is a circuit block diagram which shows one structural example which implement | achieved the variable capacitance circuit in which the area | region which shows a negative capacity does not exist. It is a circuit diagram which shows the circuit structure of the negative impedance converter circuit comprised using the operational amplifier. FIG. 7 is a circuit diagram showing a circuit configuration of a negative capacitance circuit in which the negative impedance conversion circuit shown in FIG. 6 is combined with a circuit for differentially operating the first and second variable capacitance diodes. It is a circuit diagram which shows an example of a structure of the negative capacity circuit using the negative impedance conversion circuit which does not reduce the gain of an amplification stage. It is a circuit diagram which shows another example of a structure of the negative capacitance circuit using the negative impedance conversion circuit which does not reduce the gain of an amplification stage.

Explanation of symbols

1a, 11a, 21a Non-grounded input terminal 1b, 11b, 21b Grounded input terminal 2 Variable capacitance diode 3, 14, 28, 35 Negative impedance conversion circuit (NCC)
4, 15 Input coupling capacitance 5 Load capacitance 6, 16a, 16b Controllable voltage generator 7, 17a, 17b Buffer resistor 12 First variable capacitance diode 13 Second variable capacitance diode 18 Output coupling capacitance 19 Bypass capacitance 20 Additional capacitance 22 Operational amplifiers 23, 24, 25 Impedance 26 Coupling capacity 27 Resistive elements 29 ₁ , 29 ₂ Pair of input transistors 30, 37 Output transistors 31, 32, 38, 41 Capacitance elements 33, 34, 39, 40 Feedback resistances 36 ₁ , 36 ₂ pairs of Darlington-connected composite transistors

Claims (5)

A negative impedance connected between a non-ground side input terminal and a ground side input terminal and having a variable capacitance voltage supplied with a variable control voltage output from a controllable voltage generator, an input end, an output end, and a ground end A negative impedance conversion circuit, wherein the input end is connected to the non-ground side input terminal, and the output end is connected to the ground side input terminal via a capacitive element. Is selected to be approximately equal to the distributed capacitance value formed between the non-grounded input terminal and the grounded input terminal, thereby adjusting the controllable voltage by adjusting the controllable voltage generator. A variable capacitance circuit, wherein the capacitance value of the variable capacitance diode is changed logarithmically as the variable control voltage output from the device is linearly changed. A first variable capacitance diode connected between the non-ground side input terminal and the ground side input terminal and supplied with a first variable control voltage output from the controllable voltage generator; an input end, an output end, and a ground end The input terminal is connected to the non-grounded input terminal, and the output terminal is supplied with a second variable control voltage output from the controllable voltage generator. A negative impedance conversion circuit connected to the ground-side input terminal via a second variable capacitance diode capacitance element, wherein the first variable control voltage and the second variable control voltage are the controllable voltage By adjusting the forming device, the capacitance values of the first and second variable control voltages are increased and decreased in opposite directions, and the capacitance values of the first and second variable control voltages are changed in the opposite directions, thereby being output from the controllable voltage forming device. The total capacitance value of the first and second variable capacitance diodes is formed so as to change linearly in the positive and negative capacitance regions as the first and second variable control voltages change linearly. Variable capacitance circuit. A fixed capacitance element is additionally connected in parallel with the first variable capacitance diode between the non-ground side input terminal and the ground side input terminal, and the capacitance value of the fixed capacitance element is changed between the first and second variable capacitance elements. 3. The total capacitance value of the first and second variable capacitance diodes is selected to be a value that linearly changes only in the positive capacitance region as the control voltage is linearly changed. Variable capacitance circuit. The negative impedance conversion circuit includes an operational amplifier, a first impedance connected between one input end and an output end, a second impedance connected between the other input end and the output end, and the other 4. The variable capacitance circuit according to claim 1, wherein the variable capacitance circuit is configured by a third impedance connected between one input end and a grounding point. 5. The negative impedance conversion circuit is connected between a first input terminal and an output terminal of a differential amplifier having first and second input terminals and one output terminal configured using individual amplifying elements. A first impedance, a second impedance connected between the second input terminal and the output terminal, and a third impedance connected between the second input terminal and the grounding point. The variable capacitance circuit according to claim 1, wherein the variable capacitance circuit is provided.

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