Patent Publication Number: US-8989750-B2

Title: Control circuit, impedance adjusting circuit, impedance automatic adjusting circuit, radio transceiver circuit, control method, impedance adjusting method, impedance automatic adjusting method, and radio transceiving method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Applications No. 2012-023254, filed on Feb. 6, 2012, the entire contents of which are herein incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a control circuit and a control method which can control at least one of permittivity and permeability. The invention also relates to an impedance adjusting circuit, an impedance automatic adjusting circuit, a radio transceiver circuit, a control method, an impedance adjusting method, an impedance automatic adjusting method, and a radio transceiving method. 
     2. Related Art 
     Permittivity and permeability have prescribed physical influences on signals such as an electric signal which flows through a signal path of an electric circuit and a radio signal for radio transmission or reception. For example, permittivity and permeability influence an electric signal in such a manner as to change its amplitude, phase, delay, or the like. For another example, a characteristic of an electric circuit can be controlled by controlling permittivity. In this connection, JP-A-2003-209266 discloses a technique for varying the capacitance of a capacitance component by controlling permittivity. 
     As described above, permittivity and permeability have prescribed physical influences on an electric signal and a radio signal and change their amplitudes, phases, delays, or the like. That is, if permittivity or permeability can be controlled in a desired manner, a desired influence can be given to a signal such as an electric signal or a radio signal. 
     In the technique of JP-A-2003-209266, to control the permittivity of a dielectric crystal in a desired manner, it is necessary to not only apply, to the dielectric crystal, light whose energy is equal to the band gap energy of the dielectric crystal but also apply an electric field to the dielectric crystal. This requires a complex configuration and control. 
     SUMMARY OF THE INVENTION 
     One or more illustrative aspects of the present invention are to give a signal a desired influence by controlling permittivity or permeability by a simple control. 
     According to one or more illustrative aspects of the present invention, there is provided a control circuit ( 1 ) comprising: a cell area ( 2 A) comprising a plurality of cells ( 2 ) arranged therein, each of the cells comprising: a first conductor ( 3 ) having at least one capacitance component (C 1 , C 2 ); a second conductor ( 4 ) connected to the first conductor and having an inductance component; and a feed line ( 5 ) provided to be in non-contact with the first conductor and the second conductor, wherein a size of each of the cells is smaller than a wavelength of a signal to be influenced by the cells; and at least one feed controller ( 6 ) configured to control at least one of permittivity and permeability of the cell area by changing the amount of a power supply provided to the feed line of each of the cells. 
     According to one or more illustrative aspects of the present invention, the second conductor is formed as a via conductor which is short-circuited to a common potential for the respective cells, and the feed line is in non-contact with the via conductor. 
     According to one or more illustrative aspects of the present invention, the first conductor is formed in an approximately 8-shape having at least one air gap. 
     According to one or more illustrative aspects of the present invention, there is provided an impedance adjusting circuit ( 12 ,  13 ,  36 ) comprising: the control circuit ( 1 ); and a signal line ( 15 , 16 ) which is in non-contact with the cell area, wherein the control circuit is configured to control the permittivity of the cell area so as to obtain a desired characteristic impedance of a signal transmitted through the signal line. 
     According to one or more illustrative aspects of the present invention, there is provided an impedance automatic adjusting circuit ( 30 ) comprising: the impedance adjusting circuit ( 36 ); a detector ( 39 ) configured to detect, for different power supply values, a level of the signal that is output from the impedance adjusting circuit; and a power supply value setting unit ( 43 ) configured to set a power supply value corresponding to a desired level of the signal in the feed controller ( 6 ). 
     According to one or more illustrative aspects of the present invention, the impedance automatic adjusting circuit further comprises: a storage unit ( 44 ) configured to store power supply values and levels of the signal detected by the detector such that each of the power supply values is associated with a corresponding one of the levels of the signal. The power supply value setting unit ( 43 ) is configured to set, in the feed controller ( 6 ), the power supply value corresponding to the desired level of the signal, which is stored in the storage unit. 
     According to one or more illustrative aspects of the present invention, the impedance automatic adjusting circuit further comprises: a level controller ( 40 ,  41 ,  42 ) configured to control the power supply value such that the level of the signal detected by the detector is coincident with the level of the signal corresponding to the power supply value set by the power supply value setting unit. 
     According to one or more illustrative aspects of the present invention, there is provided a radio transceiver circuit ( 51 ). The radio transceiver circuit ( 51 ) comprises: the control circuit ( 1 ); and an antenna ( 53 ) configured to transmit and receive a radio signal having a certain frequency, wherein the cell area ( 2 A) of the control circuit is provided around the antenna, and wherein the feed controller ( 6 ) controls the permittivity of the cell area such that the radio signal having the certain frequency is allowed to pass through the cell area and radio signals having frequencies other than the certain frequency are reflected by the cell area. 
     According to one or more illustrative aspects of the present invention, the control circuit ( 1 ) comprises first and second control circuits, and a cell area ( 2 A) of the first control circuit is formed on a first layer, a cell area ( 2 A) of the second control circuit is formed on a second layer, and the antenna ( 53 ) is formed on a third layer which is located between the first and second layers. 
     According to one or more illustrative aspects of the present invention, the radio transceiver circuit further comprises: a power supply value setting unit ( 71 ) configured to measure a reception level of the radio signal having the certain frequency, which is received by the antenna, and to set a power supply value corresponding to the measured reception level of the radio signal in the feed controller. 
     According to one or more illustrative aspects of the present invention, if a first power supply value corresponding to a first reception level of the radio signal having the certain frequency is set in the feed controller in advance, the power supply value setting unit: i) measure a second reception level of the radio signal having the certain frequency, which corresponds to a second power supply value, wherein the second power supply value is larger than the first power supply value; ii) set the second power supply value in the feed controller, if the second reception level corresponding to the second power supply value is larger than the first reception level corresponding to the first power supply value; and iii) set the first power supply value in the feed controller, if the second reception level corresponding to the second power supply value is smaller than the first reception level corresponding to the first power supply value. 
     According to one or more illustrative aspects of the present invention, the control circuit is integrated in one chip. 
     According to one or more illustrative aspects of the present invention, there is provided a control method of controlling at least one of permittivity and permeability of a cell area ( 2 A) comprising a plurality of cells ( 2 ) arranged therein, each of the cells comprising: a first conductor ( 3 ) having at least one capacitance component (C 1 , C 2 ), a second conductor ( 4 ) connected to the first conductor and having an inductance component; and a feed line ( 5 ) provided to be in non-contact with the first conductor and the second conductor, wherein a size of each of the cells is smaller than a wavelength of a signal to be influenced by the cells. The control method comprises: controlling at least one of permittivity and permeability of the cell area by changing the amount of a power supply provided to the feed line of each of the cells. 
     According to one or more illustrative aspects of the present invention, there is provided an impedance adjusting method using the control method, comprising: controlling the permittivity of the cell area so as to obtain a desired characteristic impedance of a signal transmitted through a signal line which is in non-contact with the cell area. 
     According to one or more illustrative aspects of the present invention, there is provided an impedance automatic adjusting method using the impedance adjusting method, comprising: detecting a level of the signal for different power supply values; and setting a power supply value corresponding to a desired level of the signal, when the detected level of the signal reaches the desired level. 
     According to one or more illustrative aspects of the present invention, the impedance automatic adjusting method further comprises: controlling the power supply value such that the detected level of the signal is coincident with the level of the signal corresponding to the set power supply value. 
     According to one or more illustrative aspects of the present invention, there is provided a radio transceiving method of transceiving a radio signal having a certain frequency with an antenna ( 53 ) by using the control method, wherein the antenna ( 53 ) is configured to transmit and receive a radio signal having a certain frequency, and the cell area ( 2 A) is provided around the antenna. The method comprises: controlling the permittivity of the cell area such that the radio signal having the certain frequency is allowed to pass through the cell area and radio signals having frequencies other than the certain frequency are reflected by the cell area; and transceiving the radio signal having the certain frequency with the antenna. 
     According to one or more illustrative aspects of the present invention, the radio transceiving method further comprises: measuring a reception level of the radio signal having the certain frequency, which is received by the antenna; and setting a power supply value corresponding to the measured reception level. 
     According to the present invention, the permittivity or permeability of the cell area and its neighboring space is controlled by controlling the amounts of power supplied to the respective feed lines. The control of the permittivity or permeability makes it possible to give a desired influence on a signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cell area of a control circuit according to an embodiment; 
         FIG. 2  shows the structure of each cell used in the embodiment; 
         FIGS. 3A and 3B  are a side view and a top view, respectively, of a signal input/output circuit of Example 1; 
         FIG. 4  is a circuit diagram showing an impedance automatic adjusting circuit and a signal level adjusting circuit of Example 2; 
         FIG. 5  is a functional block diagram corresponding to part of the circuit of  FIG. 4 ; 
         FIG. 6  shows an example radio transceiver circuit of Example 3; 
         FIG. 7  shows another example radio transceiver circuit of Example 3; 
         FIG. 8  shows a radio transmission/reception automatic adjusting circuit of Example 4; 
         FIG. 9  is a graph showing a relationship between the reception level of a radio signal and the amount of supply power; and 
         FIG. 10  shows a chip of Example 5. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An embodiment of the present invention will be hereinafter described.  FIG. 1  shows a control circuit  1  according to the embodiment. As shown in  FIG. 1 , the control circuit  1  is configured such that a large number of cells  2  are arranged two-dimensionally (i.e., in the vertical and horizontal directions) on a substrate (not shown). Alternatively, cells  2  may be arranged one-dimensionally or three-dimensionally. In the embodiment, an area where the cells  2  are arranged two-dimensionally is called a cell area  2 A and the control circuit  1  is mainly formed by the cell area  2 A. 
     The cell area  2 A can function as a CRLH (composite right and left handed) structure. CRLH structures are composite structures of a right-handed (RH) system structure in which permittivity and permeability have positive values and a left-handed (LH) system structure in which permittivity and permeability have negative values. Whereas right-handed systems structures behave like natural substances, left-handed system structures behave in manners that are not found in nature. Thus, left-handed system structures are composed of artificial substances. Left-handed system structures are called metamaterials. 
     Each cell  2  has a structure shown in  FIG. 2  and is extremely small in size. The control circuit  1  is a circuit that is constructed to give a prescribed influence on an electric signal flowing in an electric circuit or a radio signal (hereinafter referred to simple as a signal). The size of each cell  2  should be at least smaller than the wavelength λ of a signal. It is even preferable that the size of each cell  2  be sufficiently smaller than (e.g., ⅛ of) the wavelength λ, of a signal. 
     Each cell  2  is composed of a first conductor  3 , a second conductor  4 , and a feed line  5 . The first conductor  3  is provided so that a surface current flows through it and is made of a conductive substance. The first conductor  3  includes at least one capacitance. To satisfy this condition, the first conductor  3  is approximately shaped like a numeral “8” and has two gaps C 1  and C 2  at the top and the bottom, respectively. Capacitances are formed by the respective gaps C 1  and C 2 . 
     It suffices that the first conductor  3  be made of a conductive substance and include at least one capacitance; the first conductor  3  may have an arbitrary shape such as an approximately rectangular shape, an approximately triangular shape, or a prescribed planar shape. Whatever shape the first conductor  3  has, it should include at least one capacitance. The position of the at least one capacitance is not restricted as long as it is formed at a certain position in the first conductor  3 . Example dimensions representing the size of each cell  2  are the lengths of its respective sides (e.g., the vertical and horizontal lengths of the first conductor  3  across the plane and the longitudinal length of the feed line  5  in each cell  2 ). 
     The second conductor  4  is formed as a via (through-hole) conductor so as to extend in the direction that is perpendicular to the paper surface of  FIG. 2 . Although in  FIG. 2  the second conductor  4  is formed at the intersection of the two diagonal elements of the approximately 8-shaped first conductor  3 , the second conductor  4  may be formed at an arbitrary position in the first conductor  3 . The second conductor  4  is short-circuited to a common potential (e.g., ground layer GND (described later)) to become a short stub. As a result, the second conductor  4  has an inductance. The second conductor  4  may be a conductor other than a via conductor as long as it has an inductance. 
     The feed line  5  is a current flowing line. The feed line  5  is placed at a different height position than the first conductor  3  in the direction that is perpendicular to the paper surface of  FIG. 2 . As a result, the first conductor  3  and the feed line  5  are not in contact with each other. The feed line  5  is not in contact with the second conductor  4  either. To this end, the feed line  5  has a through-hole which is larger in diameter than the second conductor  4  and the second conductor  4  is inserted through this through-hole so as not be in contact with the feed line  5 . 
     A feed controller  6  is connected to the feed line  5 . The feed controller  6  not only serves as a current source for supplying power to the feed line  5  to cause a current to flow through it, but also can control the supply power (current) to a proper value. Although in  FIG. 2  the feed controller  6  is connected to the feed line  5  to supply power to it (contact power supply), a non-contact power supply method may be employed. 
     Feed controllers  6  may be provided so as to supply power to all of the large number of cells  2  individually. Alternatively, a single feed controller  6  may supply power to a prescribed number of cells  2  of all of the large number of cells  2 . For example, a single feed controller  6  may supply power to the feed lines  5  of plural cells that are arranged in one row. An arbitrary power supply method may be employed such as power supply by radiation of radio waves. As a further alternative, a single feed controller  6  may supply power to all the cells  2 . 
     Therefore, depending on the manner of power supply to the cells  2 , feed controllers  6  may be provided in either the same number as or a smaller number than the cells. That is, at least one feed controller  6  is provided. 
     When the feed line  5  is supplied with power, a current flows through it (the current may be either a high-frequency current or a low-frequency current). As a result, as shown in  FIG. 2 , a magnetic field M is generated, as a result of which a surface current flows through the first conductor  3 . The magnitude of the surface current is proportional to the amount of power supplied to (i.e., the current flowing through) the feed line  5 . 
     Since the surface current flows through the first conductor  3 , charge is accumulated in the capacitances C 1  and C 2  and a current flows through the second conductor  4 . In this manner, an LC resonance circuit is formed which has a prescribed resonance frequency which depends on the amount of power supplied to the feed line  5 . Since each cell  2  constitutes an LC resonance circuit, an arrangement of a large number of LC resonance circuits is formed by arranging the large number of cells  2  in the vertical and horizontal directions. 
     The cells  2  are arranged such that adjoining ones are close to each other and are not in contact with each other. As a result, a stray capacitance is generated between each cell  2  and the cells  2  around it. This stray capacitance constitutes part of the capacitance of the LC resonance circuit. Since the stray capacitance depends on the surface current flowing through the first conductor  3 , it is proportional to the amount of power supplied to the feed line  5 . 
     The cell area  2 A having a prescribed area is formed by arranging the large number of minute cells  2  which are sufficiently smaller than the wavelength λ of a signal, two-dimensionally such that they are close to each other and are not in contact with each other. That is, a large number of minute LC resonance circuits are arranged in array in the cell area  2 A. This structure can function as a CRLH structure. 
     The feed controllers  6  supply power to the feed lines  5  of the respective cells  2  of the cell area  2 A. As a result, resonance occurs in each LC resonance circuit and the permittivity (and permeability) of the cell area  2 A and its neighboring space is determined. The permittivity is varied by varying the amounts of power supplied from the feed controllers  6 . That is, the permittivity of the cell area  2 A and its neighboring space can be controlled by controlling the supply power. 
     As described above, the cell area  2 A is configured as an arrangement of the large number of cells  2  (LC resonance circuits) and its permittivity can be controlled according to the amount of power supplied to it. Not only the permittivity of the cell area  2 A but also its permeability can be controlled by the amount of power supplied to it. Therefore, it is possible to give a signal a prescribed influence (e.g., cause a change in amplitude, phase, delay, or the like) by controlling one or both of the permittivity and permeability of the cell area  2 A. 
     In Examples described below, permeability is controlled according to the amount of supply power, whereby various workings and advantages are obtained. Since as described above permeability can also be controlled by controlling the amount of supply power, the control circuit  1  according to the embodiment can be applied to a circuit in which control is made so as to attain a desired permeability value. 
     As described above, in the control circuit  1  according to the embodiment, the amount of power supplied to the feed line  5  of each of the cells  2  constituting the cell area  2 A is controlled, whereby the permittivity or permeability of the cell area  2 A and its neighboring space can be controlled in a desired manner. While a signal passes through the permittivity or permeability-controlled space, the controlled permittivity or permeability influences the signal, that is, varies its amplitude, phase, delay, or the like. In this manner, a desired influence can be given to the signal by controlling the permittivity or permeability. 
     EXAMPLE 1 
     Next, a description will be made of Example 1 which is an application example of the above-described control circuit  1 . Example 1 is directed to impedance adjusting circuits each of which makes an impedance adjustment, in particular, impedance matching. These impedance adjusting circuits can be applied to any circuit which requires an impedance adjustment.  FIGS. 3A and 3B  are a side view and a top view, respectively, of a signal input/output circuit  10  to which the impedance adjusting circuit is applied. 
     As shown in  FIGS. 3A and 3B , the signal input/output circuit  10  has a DUT (device under test)  11  which is a circuit that requires impedance matching and an input-side impedance adjusting circuit  12  and an output-side impedance adjusting circuit  13  which are connected to the input side portion and the output side portion of the DUT  11 . The DUT  11  is a prescribed circuit which is a non-linear device. The DUT  11  may be an arbitrary circuit such as an FET (field-effect transistor), an RF (radio-frequency) filter, or an RF (radio-frequency) switch. 
     As shown in  FIG. 3A , each of the input-side impedance adjusting circuit  12  and the output-side impedance adjusting circuit  13  has a multi-layered (4-layer) structure. A first layer (Layer1) which is the top layer of the input-side impedance adjusting circuit  12  is a layer in which an input-side signal line  15  is formed. A second layer (Layer2) is a layer in which a control circuit  1  is formed. A third layer (Layer3) is a layer in which another control circuit  1  is formed. A fourth layer (Layer4) which is the bottom layer is a short-circuiting layer, that is, a common potential layer (ground layer GND). 
     As described in the above embodiment, each cell  2  of the cell area  2 A of each control circuit  1  has the second conductor  4 . As shown in  FIG. 3A , the second conductors  4  which are via conductors are short-circuited by the ground layer GND of the bottom layer. As a result, the second conductors  4  function as an inductance. 
     The input-side impedance adjusting circuit  12  and the output-side impedance adjusting circuit  13  are impedance adjusting circuits of this Example 1. Although both of the input-side impedance adjusting circuit  12  and the output-side impedance adjusting circuit  13  are provided in  FIGS. 3A and 3B , only one of them may be provided. However, using the impedance adjusting circuit of this Example 1 on both of the input side and the output side enables matching of the input impedance and the output impedance. 
     A signal S is input to and output from the DUT  11 . It is necessary to make input and output impedance matching of the DUT  11  for the signal S. This impedance matching prevents power loss of the signal S and thereby enables normal input and output of the signal S. In other words, if this impedance matching were not made, part of the signal S would be reflected to cause a power loss and the signal S would not be input or output normally. 
     Thus, it is necessary that the DUT  11  be provided with an impedance matching circuit on both of the input side and the output side. Conventionally, such an impedance matching circuit needs to be designed for each frequency band of the signal S using, specifically, an LC circuit or the like. However, designing of such an impedance matching circuit is very difficult and takes time. And designed impedance matching circuits tend to vary in performance to a large extent depending on the skills of designers. 
     There are other factors that make it difficult to attain desired impedance matching, such as a prepreg and the thickness of a substrate used in an actual impedance matching circuit, a permittivity variation, and the accuracy of etching that is performed in circuit formation. Another problem is that the size of an impedance matching circuit becomes too large depending on the frequency range of a signal S. Thus, it is difficult to design and manufacture a desired impedance matching circuit. 
     In this Example 1, impedance matching is made using the above-described control circuit  1  rather than a conventional impedance matching circuit. As shown in  FIG. 3B , a signal S is input through an input port  14 , transmitted through the input-side signal line  15 , and input to the DUT  11 . 
     The control circuit  1  is mainly composed of the cell area  2 A, and the feed controller (feed controllers  6 ) control the amounts of supply power to control the permittivity of the cell area  2 A and its neighboring space. The control circuit  1  which is formed in the second layer is located close to the input-side signal line  15  which is in the first layer, and the permittivity as controlled by the control circuit  1  influences the signal S being transmitted through the input-side signal line  15 . 
     The characteristic impedance for the signal S varies being influenced by permittivity. Therefore, the characteristic impedance for the signal S varies when the permittivity as controlled by the control circuit  1  influences the signal S being transmitted through the input-side signal line  15 . The characteristic impedance is adjusted by controlling the amount of supply power to the control circuit  1  (feed lines  5 ). 
     That is, the feed controller of the control circuit  1  control the amounts of supply power so as to produce such a permittivity value that the characteristic impedance for the signal S becomes a desired value. In particular, a matched characteristic impedance is obtained by controlling the amounts of supply power properly. Impedance matching may be made such that the feed controller control the permittivity so that the impedance of the input-side signal line  15  becomes equal to the characteristic impedance for the signal S being transmitted through the input-side signal line  15 . 
     As a result, impedance matching can be attained on the input side and the power loss of the signal S to be input to the DUT  11  can be controlled intentionally. The same effect can be obtained also by the output-side impedance adjusting circuit  13 . Impedance matching can be made on both of the input side and the output side. Thus, a high-quality signal S whose power loss has been controlled intentionally can be output from an output port  17 . 
     As described above, in this Example 1, impedance matching for a signal S is made merely by dynamically varying the amount of power supplied to the cell area  2 A without designing and manufacturing an LC circuit or the like. In this manner, impedance matching can be made by a method that is different in concept from the conventional method for designing and manufacturing an impedance matching circuit. That is, impedance matching can be made merely by dynamically controlling the amounts of power supplied from the feed controller. 
     The control circuit  1  which is formed in the third layer (Layer3) as shown in  FIG. 3A  operates in the same manner and provides the same advantage as the control circuit  1  formed in the second layer (Layer2). In addition, the control circuit  1  formed in the third layer can provide a function of shielding the printed circuit board from an outside phenomenon occurring on the side of the ground layer GND. The amount of supply power of the control circuit  1  can be controlled so as to produce such a permittivity value that the control circuit  1  exhibits such a shield function. However, this shield function is not indispensable for this Example 1 and the third layer may be omitted. 
     Although the input-side impedance adjusting circuit  12  has the 4-layer structure, the structure of the input-side impedance adjusting circuit  12  is not limited to it. Although the control circuits  1  are formed in the second layer and the third layer, a control circuit  1  may be formed in the first layer or the fourth layer. Although the input-side signal line  15  and the output-side signal line  16  are formed in the top layer of the control circuit  1 , they may be formed in the bottom layer and they may be formed in different layers. Any of the above modifications can provide the same advantage as described above. 
     Each of the input-side impedance adjusting circuit  12  and the output-side impedance adjusting circuit  13  attains impedance matching for a signal S by controlling the amount of supply power to an optimum value. Although this is a most desirable mode, an adjustment may be made so as to increase the degree of matching to a level that is lower than the level of complete matching. In short, it suffices that the characteristic impedance for a signal S be adjusted to a desired value. 
     EXAMPLE 2 
     Next, a description will be made of Example 2 to which the impedance adjusting circuit of Example 1 is applied. In Example 2, an impedance adjustment is performed automatically.  FIG. 4  shows an impedance automatic adjusting circuit  30  of Example 2, which is equipped with an input port  31 , an amplifier block  32 , a lowpass filter  33 , an amplifier  34 , an isolator  35 , an impedance adjusting circuit  36 , a variable attenuator  37 , an antenna  38 , a detector  39 , a DAC  40 , a switch  41 , and a comparator  42 . 
     A signal S is input through the input port  31 . The amplifier block  32  amplifies the signal S. The amplifier block  32  has an external terminal which enables level adjustment (amplification factor adjustment). The lowpass filter  33  eliminates a high-frequency component. The amplifier  34  amplifies the signal S at a prescribed amplification factor. The isolator  35  is an irreversible circuit element which passes the signal S going toward the impedance adjusting circuit  36  while stopping a signal which goes in the opposite direction. 
     The impedance adjusting circuit  36  is a circuit which is equivalent to the impedance adjusting circuit described in Example 1 (input-side impedance adjusting circuit  12  and/or output-side impedance adjusting circuit  13 ). The variable attenuator  37  is a circuit which can control the degree of attenuation of the signal S. The antenna  38  transmits the signal S in the form of radio waves. 
     The detector  39  detects a level (intensity) of the signal S at the output side of the impedance adjusting circuit  36 . The level of the signal S is its power, voltage, current, or the like. The DAC (digital-to-analog converter)  40  can output an arbitrary current (or voltage). The DAC  40  serves as a power supply value output unit. 
     The switch  41  connects the output of the DAC  40  to the impedance adjusting circuit  36  or the comparator  42 . When connected to the DAC  40  via the switch  41 , the comparator  42  compares a level of the signal S detected by the detector  39  with an output value of the DAC  40  and outputs a comparison result to the external terminal of the amplifier block  32 . 
       FIG. 5  is a functional block diagram corresponding to part of the circuit of  FIG. 4 . As shown in the block diagram of  FIG. 5 , a power supply value setting unit  43  has the DAC  40  (power supply value output unit) and a level determining unit  45 . A storage unit  44  is connected to the power supply value setting unit  43 . The other part of the circuit partly shown in  FIG. 5  is the same as the corresponding part of the circuit of  FIG. 4 . Impedance automatic adjustment and signal level adjustment will be described below in order. 
     [Impedance Automatic Adjustment] 
     While the switch  41  is switched to the impedance adjusting circuit  36 , the DAC  40  of the power supply value setting unit  43  outputs a power supply value. The impedance adjusting circuit  36  has the control circuit  1  according to the embodiment, and amounts of power of the feed controllers  6  of the control circuit  1  are set. 
     The DAC  40  of the power supply value setting unit  43  can vary the power supply value (current value) and set arbitrary power supply values in the feed controllers  6 . The level determining unit  45  judges a level, detected by the detector  39 , of the signal S. Since the level detected by the detector  39  varies according to the amount of supply power, power supply values and detected levels of the signal S are stored in the storage unit  44  such that each of the power supply values is associated with a corresponding one of the detected levels of the signal S. 
     Next, a description will be made of how the impedance automatic adjusting circuit  30  operates. As shown in  FIG. 4 , a signal S that is input through the input port  31  passes through the amplifier block  32 , whereby its level is adjusted to a prescribed level. A high-frequency component is eliminated from the signal S, whereby the signal S becomes a low-frequency signal. The signal S passes through the isolator  35  and is input to the impedance adjusting circuit  36 . 
     The signal S for which the characteristic impedance has been adjusted by the impedance adjusting circuit  36  is level-detected by the detector  39 . The level of the signal S is adjusted by the variable attenuator  37 . The level-adjusted signal S is transmitted from the antenna  38  as radio waves. 
     A level of the output signal of the impedance adjusting circuit  36  is detected by the detector  39 . At the beginning, the DAC  40  is connected to the impedance adjusting circuit  36  by the switch  41 . A current that is output from the DAC  40  is set in the feed controllers  6  of the impedance adjusting circuit  36 . Supply power having the thus-set value is supplied to the feed lines  5  of the respective cells  2 . In this manner, the amounts of power supplied to the feed lines  5  of the cells  2 , respectively, can be varied. The DAC  40  increases or decreases the output current gradually and causes the amounts of power supplied from the feed controllers  6  to vary accordingly. 
     As the amounts of supply power are varied, the permittivity of the cell area  2 A and its neighboring space is varied, whereby the characteristic impedance for the signal S is varied. Characteristic impedance matching is not made, the level of the signal S detected by the detector  39  becomes low. When the amounts of supply power are varied, the permittivity and hence the characteristic impedance is varied. 
     The DAC  40  varies the power supply value gradually. In response, the characteristic impedance for the signal S is varied and, resultantly, the level of the signal S detected by the detector  39  is varied. Whereas at first the level of the signal S is detected a low level, the level of the signal S increases as the impedance matching progresses. The detection level of the detector  39  is maximized when the characteristic impedance matching for the signal S is completed. Impedance matching is made and the detection level is maximized also when the impedance of the above-described input-side signal line  15  becomes equal to the characteristic impedance for the signal S being transmitted through the input-side signal line  15 . 
     As described above, the amounts of power supplied from the feed controllers  6  of the impedance adjusting circuit  36  are varied by varying the power supply value that is output from the DAC  40 . And the detection level of the detector  39  is varied accordingly. The power supply value setting unit  43  is equipped with the DAC  40  and the level determining unit  45 , and stores output current values (power supply values) of the DAC  40  and corresponding detection levels of the detector  39  in the storage unit  44  in pairs. A power supply value corresponding to a maximum detection level of the detector  39  is also stored in the storage unit  44 . 
     In this manner, power supply values and detection levels are stored in the storage unit  44  in pairs. A power supply value corresponding to a desired level of the signal S (detection level) is read from the storage unit  44 , and the DAC  40  sets the read-out power supply value in the feed controllers  6  of the impedance adjusting circuit  36 . 
     The feed controllers  6  continue to supply the feed lines  5  with power having the thus-set value, whereby the level of the signal S can be kept at the desired value. In the above-described operation, levels of the signal S that are detected by the detector  39  as the DAC  40  varies the power supply value. And the power supply value setting unit  43  sets, in the feed controllers  6  of the impedance adjusting circuit  36 , such a power supply value that the signal S is given a desired level. Therefore, an impedance adjustment can be performed automatically. 
     When a power supply value that maximizes the detection level of the detector  39  is set in the feed controllers  6 , impedance matching is attained automatically and the power loss of the signal S is minimized. However, it is not always necessary to attain complete impedance matching; a control may be made so as to obtain a desired impedance value. In the above-described operation, power supply values and signal levels are stored in the storage unit  44  in pairs and a power supply value corresponding to a desired level is thereafter read out and set. Alternatively, without using the storage unit  44 , the power supply value setting unit  43  may set a power supply value at a time point when the level of the signal S detected by the detector  39  has become a desired level. 
     Although in the above configuration the power supply value output unit is the DAC  40  which varies the power supply value, instead of being the DAC  40  the power supply value output unit may be configured so as to be able to set a power supply value digitally. That is, the power supply value output unit may be such as to set digital data indicating a power supply value in the feed controllers  6  of the impedance adjusting circuit  36 . 
     The power supply value setting unit  43  may be such as to merely issue, to the feed controllers  6  of the impedance adjusting circuit  36 , an instruction to vary the amounts of supply power. In response, the feed controllers  6  vary the amounts of supply power. The power supply value setting unit  43  causes the feed controllers  6  to stop varying the amounts of supply power when the level of the signal S detected by the detector  39  has become a desired level, whereby an automatic adjustment can be performed so as to realize a desired impedance value. 
     With the above operation, the impedance adjusting circuit  36  can realize a desired impedance value. In this operation, it is assumed that a control is performed so as to attain impedance matching. Next, the switch  41  is switched so as to connect the DAC  40  to the comparator  42  (the DAC  40  has been connected to the impedance adjusting circuit  36  so far). As a result, an output value of the DAC  40  and a detection level of the detector  39  are input to the comparator  42 . 
     [Signal Level Adjustment] 
     After the switching of the switch  41 , the DAC  40  outputs a voltage value, a power value, a current value, or the like indicating a detection level. The detection level corresponding to the power supply value that was set in the feed controllers  6  of the impedance adjusting circuit  36  is stored in the storage unit  44  which is connected to the power supply value setting unit  43 . 
     The DAC  40  outputs the above detection level (voltage value, power value, current value, or the like). The detection level that is output from the DAC  40  is input to the comparator  42 . The detection level of the detector  39  is also input to the comparator  42 . The two detection levels that are input to the comparator  42  are identical. This is because the detector  39  detects a level of the signal S that is determined by the power supply value that was set by the power supply value setting unit  43  and the DAC  40  outputs the detection level corresponding to the power supply value. 
     Therefore, basically, the result of the comparison between the two detection levels by the comparator  42  should be “identical.” This comparison result is maintained as long as the level of the signal S is stable. However, the comparison result of the comparator  42  becomes “not identical” if the level of the signal S varies due to, for example, a certain disturbance (e.g., if the level of the signal S lowers when the gain of each circuit decreases due to a temperature variation). 
     In view of the above, the comparator  42  performs a level adjustment on the signal S using the amplifier block  32 . This makes it possible to always transmit the signal S at a constant level from the antenna  38  even if a level variation has occurred in the signal S. For example, when the level of the signal S detected by the detector  39  has lowered (or risen) due to, for example, a disturbance, the comparator  42  performs a level adjustment so that the level of the signal S is always kept constant by increasing (or decreasing) the amplification factor of the amplifier block  32 . Thus, an AGC (automatic gain control) function is realized by the operation that the comparator  42  controls the amplifier block  32  based on the level of the signal S detected by the detector  39 . This makes it possible to always output the signal S at a constant level. 
     The circuit which performs the above AGC is a signal level adjusting circuit which can keep the level of the signal S stable. The comparator  32  and the amplifier block  32  serves as its controller. 
     As described above, in this Example 2, a control is made so that the level of the signal S detected by the detector  39  becomes a desired level by changing the amount of supply power of the impedance adjusting circuit  36 . The impedance adjustment can be performed automatically because the amount of supply power is set by changing the output current of the power supply value output unit automatically. 
     EXAMPLE 3 
     Example 3 is an application example of the control circuit  1  according to the embodiment. The control circuit  1  used in Example 3 acts on a radio signal by controlling the permittivity. More specifically, the control circuit  1  is given such a characteristic as to transmit a radio signal having a particular frequency and reflect radio signals having other frequencies. Radio transceiver circuits  50  and  60  are constructed using the control circuit  1  having such a characteristic. 
       FIG. 6  shows an example radio transceiver circuit  50 , which is equipped with a wireless communication device  51  and a control circuit  1 . The control circuit  1  is composed of a cell area  2 A and feed controllers  6  which was described in the embodiment. The wireless communication device  51  is composed of the feed controllers  6 , a communication controller  52 , and an antenna  53 . 
     The cell area  2 A is disposed around the antenna  53  so as to cover it. Thus, the wireless communication device  51  and the cell area  2 A form a closed space. The antenna  53  is disposed inside the closed space. The wireless communication device  51  is a device which is connected to the antenna  53  and controls transmission and reception of a radio signal. The antenna  53  transmits and receives a radio signal. The antenna  53  may be such as to perform only one of transmission and reception of a radio signal. 
     In the control circuit  1 , the permittivity is controlled by controlling the amounts of power supplied to the feed lines  5  of the respective cells  2  which constitute the cell area  2 A, whereby the refractive indices of the respective cells  2  are varied. The refractive index variations influence a radio signal and thereby enable its transmission or reflection. Thus, the control circuit  1  can be given such a characteristic as to transmit a radio signal having a particular frequency and reflect radio signals having other frequencies. For example, the control circuit  1  can be given such a characteristic as to transmit a radio signal of a 2-GHz band and reflect radio signals of other frequency bands. 
     The feed controllers  6  controls the amount of supply power so that the cell area  2 A and its neighboring space have the above characteristic. The cell area  2 A which is disposed around the antenna  53  transmits a radio signal F 1  having a particular frequency among radio signals F having various frequencies and reflects radio signals F 2  having the other frequencies. 
     The radio transceiver circuit  50  performs a wireless communication by transmitting and receiving radio signals F 1  having the particular frequency. On the other hand, radio signals F 2  having other frequencies become noise components and hence it is desirable to prevent the antenna  53  from receiving such radio signals F 2 . Since it is possible to allow the antenna to transmit and receive only radio signals F 1  having the particular frequency, a high-quality wireless communication can be realized. It suffices that the transmittable and receivable frequency band of the antenna  53  at least include the particular frequency. For example, even an antenna  53  which can transmit and receive not only a radio signal having the particular frequency but also radio signals of other frequency bands is made usable by employing a transmission and reception characteristics which is attained by the above-described permittivity control. That is, the frequency band of the antenna  53  is not limited to the particular frequency and a wide-band antenna can be used as the antenna  53 . Although in this Example 3 the antenna  53  is fully covered with the cell area  2 A to form a closed space, the antenna  53  may be covered partially with the cell area  2 A. 
     As shown in  FIG. 7 , it is possible to form a multi-layered radio transceiver circuit  60 . As shown in  FIG. 7 , the radio transceiver circuit  60  uses cell areas  2 A in the first layer (Layer1) and the second layer (Layer2), respectively. A third layer (Layer3) is an intermediate layer which is interposed between the first layer and the second layer. A substrate  61  and an antenna  62  are provided in the third layer. A fourth layer (Layer4) is the ground layer GND which was described in Example 1. 
     As described above, by controlling the amounts of supply power, each of the cell areas  2 A formed in the first layer and the second layer can be given such a characteristic as to transmit a radio signal F 1  having a particular frequency among radio signals F having various frequencies and reflect radio signals F 2  having the other frequencies. 
     The permittivity values are controlled so that the cell areas  2 A formed in the first layer and the second layer have the same characteristic. The substrate  61  and the antenna  62  are provided in the third layer, that is, between the first layer and the second layer. A radio signal F 1  having the particular frequency passes through the cell areas  2 A and is received by the antenna  62 , or a radio signal F 1  having the particular frequency that is emitted from the antenna  62  passes through the cell areas  2 A and is transmitted. On the other hand, radio signals F 2  having other frequencies are reflected by the cell areas  2 A and are not received by the antenna  62 . 
     In this manner, only a radio signal F 1  having the particular frequency can be transmitted and received by the antenna  62  whereas radio signals F 2  having other frequencies are reflected as noise components and not received by the antenna  62 . As a result, high-quality wireless communication can be realized. 
     Although in the above Example 3 both of the cell areas  2 A formed in the first layer and the second layer are given such a characteristic as to transmit only a radio signal F 1  having a particular frequency and reflect radio signals F 2  having other frequencies, the permittivity values may be controlled so that one of the cell areas  2 A formed in the first layer and the second layer is given such a characteristic as to interrupt radio signals F of all frequencies. 
     Even in this case, only the radio signal F 1  having the particular frequency is received by the antenna  62  whereas the radio signals F 2  having other frequencies that will become noise components are not received by the antenna  62 . Therefore, a good wireless communication is enabled by interposing, between the first layer and the second layer, the third layer which is provided with the antenna  62 . 
     EXAMPLE 4 
     Example 4 is an application example of the radio transceiver circuit  50  of Example 3.  FIG. 8  shows a radio transmission/reception automatic adjusting circuit  70  of Example 4. The radio transmission/reception automatic adjusting circuit  70  is configured such that a power supply value setting unit  71  is added to the radio transceiver circuit  50  of  FIG. 6 . The power supply value setting unit  71  is equipped with a reception level measuring unit  72  and a setting unit  73 . 
     The reception level measuring unit  72  measures a level of a radio signal F 1  having a desired frequency that is received by the antenna  53 . As described above, by controlling the amounts of power supplied from the feed controllers  6 , the control circuit  1  can be given such a characteristic as to allow a radio signal F 1  having a desired frequency to reach the antenna  53  and to reflect radio signals F 2  having other frequencies. 
     However, if the amounts of supply power are not appropriate, such a characteristic cannot be obtained. In view of this, the reception level measuring unit  72  measures a reception level of the radio signal F 1  and outputs a measurement value to the setting unit  73 . If the reception level of the radio signal F 1  having the desired frequency is low, the setting unit  73  causes the feed controllers  6  to change the amounts of supply power. 
     When the amounts of supply power are changed, the permittivity of the control circuit  1  and its neighboring space is varied. As a result, the transmittance of the radio signal F 1  having the desired frequency and the reflectance of the radio signals F 2  having other frequencies are varied.  FIG. 9  is a graph showing an example relationship between the reception level of the radio signal F 1  and the amount of supply power. 
     As seen from the graph of  FIG. 9 , as the amount of supply power is increased, the reception level of the radio signal F 1  increases and then decreases after reaching the peak. Thus, the graph is shaped like a Gaussian curve. Therefore, measuring the reception level by the reception level measuring unit  72  while the feed controllers  6  varies the amounts of supply power makes it possible to realize a characteristic of passing only the radio signal F 1  and reflecting other radio signals F 2 . 
     If the amount of supply power is set to a value corresponding to the peak shown in  FIG. 9 , the reception level of the radio signal F 1  is maximized, in which state a wireless communication can be performed with highest quality. It is therefore desirable that the amount of supply power be set to such a value as to maximize the reception level of the radio signal F 1 . However, as shown in  FIG. 9 , a wireless communication can still be performed even if the reception level of the radio signal F 1  is not at the peak value. 
     In  FIG. 9 , a horizontal broken line L 1  indicates a lower limit of a reception level range in which the radio signal F 1  can be received. Since the radio signal F 1  can be received when the reception level is higher than or equal to L 1 , a supply power range Q 1  in which the reception level is higher than or equal to L 1  is a receivable supply power range. The radio signal F 1  can be received if setting and a control are made so that the amount of power supply is set in the range Q 1 . That is, it is not always necessary to attain a maximum reception level; the reception level may be set in a certain range. 
     To set the reception level to a maximum level, the reception level measuring unit  72  measures reception levels as the amount of supply power is varied (increased or decreased gradually). If a reception level measured with a current amount of supply power that is set by the setting unit  73  is higher than a reception level obtained before a change of the amount of supply power (obtained with the preceding setting), the amount of power supply is changed further to produce the next setting. On the other hand, if the reception level measured with the current amount of supply power is lower than the reception level obtained before the change of the amount of supply power (obtained with the preceding setting), the latter reception level is judged a maximum reception level. 
     That is, the amounts of power supplied from the feed controllers  6  are varied, and a power supply value that is immediately before a power supply value with which the reception level measured by the reception level measuring unit  72  has decreased for the first time is set in the feed controllers  6 . The reception level of the radio signal F 1  can be kept at the maximum level by maintaining this setting. 
     EXAMPLE 5 
     Example 5 is directed to applications of the embodiment and Examples 1-4. The above-described various circuits can be implemented as one chip using a substrate having a relatively large permittivity value (the permittivity may be low).  FIG. 10  shows a chip  80  of Example 5, which is a one-chip version of the impedance automatic adjusting circuit  30  of Example 2. 
     It goes without saying that each of the control circuit  1  according to the embodiment, the signal input/output circuit  10  of Example 1, the level adjusting circuit of Example 2, the radio transceiver circuit  50  of Example 3, and the radio transmission/reception automatic adjusting circuit  70  of Example 4 may be implemented as one chip. Only part of each of these circuits may be implemented as one chip instead of its entirety. 
     The chip  80  shown in  FIG. 10  is equipped with an input port  82 , an output port  82 , first control ports  83 , and second control ports  84 . The input port  82  is a port for input of a signal S. An impedance adjustment for the signal S is performed automatically in the chip  80 . The signal S is output from the output port after being processing by a non-linear element such as the DUT  11 . 
     As described above, the feed controllers  6  are provided as the feed controller for controlling the amounts of power supplied to the feed lines  5  of the respective cells  2 . The feed controllers  6  are current sources and can be implemented as ports (power supply ports) provided in the first control ports  83  and the second control ports  84 . 
     Furthermore, a terminal for switching of the switch  41  and the terminal for control of the DAC  40  (see  FIG. 4 ) may be implemented as ports provided in the first control ports  83  and the second control ports  84 . Implementing the impedance automatic adjusting circuit  30  of Example 2 as one chip in the above-described manner makes it possible to reduce the circuit scale. 
     Where the chip  80  incorporates a CPU, an ALC (automatic level control) device, a variable attenuator, a VCO (voltage-controlled oscillator), a PLL (phase-locked loop), a power divider/combiner, an antenna, or the like, a port(s) for control of the incorporated device is provided in the first control ports  83  and the second control ports  84 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the sprit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and sprit of the invention.