Abstract:
A phase shifter includes a first signal path in which a first unit is disposed to advance a phase of a signal; a second signal path in which a second unit with no shunt capacitor is disposed to change the phase of the signal such that the changed phase is delayed than the advanced phase by the first unit; and a switch section configured to switch between the first signal path and said second signal path. The first unit comprises a filter, and the second unit is a transmission line.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a phase shifter and a bit phase shifter using the same. This Patent Application claims priority based on Japanese Patent application No. 2007-021725. The disclosure of the Japanese Patent application is incorporated herein by reference. 
         [0003]    2. Description of the Related Art 
         [0004]    The phased array technique has been used for special purposes such as a radar and is used in commercial products in recent years. Application of the technique is further considered to receive satellite broadcasting. A phase shifter is indispensable to use the phased array technique. In accordance with extension of application fields of the phased array technique, a demand is increasing for an inexpensive phase shifter suitable for commercial products and a satisfactory phase shifter having excellent high-frequency performance and suitable for receiving satellite broadcasting. However, it is difficult in a conventional phase shifter to satisfy requirement for the inexpensive phase shifter and requirement for the phase shifter with excellent high-frequency performance. 
         [0005]    As a switching type of phase shifter used in microwave band, an HPFLPF (high pass filter and low pass filter) switching type of phase shifter, or a switched line type of phase shifter are known. Japanese Patent No. 2679331 (first conventional example) describes a representative example of the HPFLPF switching type of phase shifter, and Japanese Laid Open Patent Application (JP-A-Heisei 7-38304) (second conventional example) describes a representative example of the switched line type of phase shifters. 
         [0006]      FIG. 1  is a circuit diagram of an HPFLPF switching type of phase shifter. Referring to  FIG. 1 , the HPFLPF switching type of phase shifter includes an input-side SPDT (single pole double throw) switch  100 , an HPF (high pass filter)  110 , an LPF (low pass filter)  112 , and an output-side SPDT switch  102 . 
         [0007]    The input-side SPDT switch  100  has an FET (field effect transistor)  110  connected to a first signal path, and an FET F 11  connected to a second signal path. In the input-side SPDT switch  100 , control voltages are applied to a control terminal CON  10  and a control terminal CON 11  in a complementary manner, respectively. That is, an OFF voltage is applied to the control terminal CON 11  when an ON voltage is applied to the control terminal CON 10 , and the ON voltage is applied to the control terminal CON 11  when the OFF voltage is applied to the control terminal CON 10 . Accordingly, the FET F 11  is in an off state when the FET F 10  in an on state, and the FET F 11  is in an on state when the FET F 10  is in an off state. 
         [0008]    The output-side SPDT switch  102  has an FET F 12  connected to the first signal path, and an FET F 13  connected to the second signal path. In the output-side SPDT switch  102 , control voltages are applied to a control terminal CON 12  and a control terminal CON 13  in a complementary manner, respectively. Since an OFF voltage is applied to the control terminal CON 13  when an ON voltage is applied to the control terminal CON 12 , the FET F 13  is in an off state when the FET F 12  is in an on state. Moreover, the ON voltage is applied to the control terminal CON 13  when the OFF voltage is applied to the control terminal CON 12 , so that the FET F 13  is in an on state when the FET F 12  is in an off state. 
         [0009]    The same control voltages are applied to the control terminal CON 10  of the input-side SPDT switch  100  and the control terminal CON 12  of the output-side SPDT switch  102 . Accordingly, the FET F 12  of the output-side SPDT switch  102  is turned on when the FET F 10  of the input-side SPDT switch  100  is turned on. At this time, the first signal path is selected. The same control voltages are also applied to the control terminal CON 11  of the input-side SPDT switch  100  and the control terminal CON 13  of the output-side SPDT switch  102 . Accordingly, the FET F 13  of the output-side SPDT switch  102  is turned on when the FET F 11  of the input-side SPDT switch  100  is turned on, and in this case the second signal path is selected. 
         [0010]    The HPF  110  is disposed in the first signal path. The HPF  110  has a shunt inductor L 10  connected to a ground, and two series-connected capacitors C 10  and C 11  are disposed to put the inductor L 10  between them. On the other hand, the LPF  112  is disposed in the second signal path. The LPF  112  has a shunt capacitor C 12  connected to a ground, and two series-connected inductors L 11  and L 12  are disposed to put the capacitor C 12  between them. 
         [0011]    When the ON voltages are applied to the control terminal CON 10  and the control terminal CON 12 , and when the OFF voltages are applied to the control terminal CON 11  and the control terminal CON 13 , a signal is inputted from an input terminal IN 10  and is outputted from an output terminal OUT 10  via the HPF  110 . At this time, the signal passes through the HPF  110 , and thereby the phase is advanced. Meanwhile, when the OFF voltages are applied to the control terminal CON 10  and the control terminal CON 12 , and when the ON voltages are applied to the control terminal CON 11  and the control terminal CON 13 , the signal inputted from the input terminal IN 10  is outputted from the output terminal OUT 10  via the LPF  112 . At this time, the signal passes through the LPF  112  and thereby its phase is delayed. 
         [0012]    In the HPFLPF switching type of phase shifter, the signal path connected to the HPF  110  and the signal path connected to the LPF  112  are switched by the SPDT switches  100  and  102 , so that a phase shift amount corresponding to a phase difference between the two signal paths can be obtained. An  10  arbitrary phase shift amount can be obtained by selecting the capacitors C 10 , C 11  and C 12  and the inductors L 10 , L 11  and L 12  to constitute the HPF  110  and the LPF  112  In a designed frequency band, a phase is advanced on an HPF  100  side, and the phase is delayed on an LPF  112  side. For example, it it is designed so that the phase on the HPF  110  side is advanced by 22.5 degrees and the phase on the LPF  112  side is delayed by 22.5 degrees at the designed frequency band, a phase shift amount of 45 degrees can be obtained. 
         [0013]      FIG. 2  is a block diagram showing a configuration of another conventional phase shifter which is generally called a switched line type of phase shifter. Referring to  FIG. 2 , the switched line type of phase shifter includes an input-side SPDT switch  104 , a first transmission line  120 , a second transmission line  122 , and an output-side SPDT switch  106 . 
         [0014]    In  FIG. 2 , when ON voltages are applied to a control terminal CON 14  and a control terminal CON 16 , and when OFF voltages are applied to a control terminal CON 15  and a control terminal CON 17 , an FET F 14  and an FET F 16  are turned on, and an FET F 15  and an FET F 17  are turned off. At this time, a signal is inputted from an input terminal IN 11  and is outputted from an output terminal OUT 11  via the transmission line  120 . Meanwhile, when the OFF voltages are applied to the control terminal CON 14  and the control terminal CON 16 , and when the ON voltages are applied to the control terminal CON 15  and the control terminal CON 17 , the FET F 14  and the FET F 16  are turned off, and the FET F 15  and the FET F 17  are turned on. At this time, the signal is inputted from the input terminal IN 11  and is outputted from the output terminal OUT 11  via the transmission line  122 . 
         [0015]    The signal paths are operationally switched through on/off control of the SPDT switches  104  and  106  in the same manner as in the circuit shown in  FIG. 1 . In the switched line type of phase shifter, a phase difference between the two signal paths can be obtained as a phase shift amount. The transmission lines  120  and  122  having different lengths are connected to the respective signal paths, and in this case, the difference between phases of the signals due to different line lengths is utilized. Since the both signal paths have phase delays, it is assumed that the transmission line  120  has a length to delay the phase by 10 degrees in the designed frequency band, and the transmission line  122  has a length to delay the phase by 55 degrees. At this time, the phase shift amount of 45 degrees can be obtained. 
         [0016]    As described above, a pair of HPF and LPF is used in the HPFLPF switching type of phase shifter and a pair of the transmission lines having different lengths is used in the switched line type of phase shifter. Other phase shifters used in a millimeter wave band include a known phase shifter described in Japanese Patent Application Publication (JP-A-Heisei 11-195960) (third conventional example). The phase shifter described in the third conventional example relates to a phase shifter in a millimeter wave band in which SPDT switch characteristics cannot be obtained, so that a signal switch is not used. Thus, it is different from phase shifters of the HPFLPF switching type and the switched line type used in a microwave band. It should be noted that since many quarter-lines (four lines at minimum) are used in the phase shifter in the third conventional example, a chip size is increased. Therefore, it is extremely difficult to fabricate an inexpensive phase shifter. 
         [0017]    A phase shifter can be configured by using either one of the conventional phase shifters, i.e. the HPFLPF switching type of phase shifter or the switched line type of phase shifter, without having any problems in the most cases. However, following problems arise depending on a specific frequency band to be used and a phase shift amount. 
         [0018]    If the phase shift amount is made smaller in the HPFLPF switching type of phase shifter, a phase shift amount advanced in a HPF and a phase shift amount delayed in an LPF need to be made smaller. In order to decrease the phase shift amounts of the filters, capacitors and inductors to constitute the filters need to have small constants. The LPF is configured of the series of inductors and the shunt capacitor, in which constants of these elements are made smaller in case of decreasing the phase shift amount. However, it is not possible in the shunt capacitor to ignore effect of a parasitic inductance caused by extending a wiring pattern in a high frequency band. Therefore, it is difficult to use a capacity of a small capacitance. In order to realize a small capacitance of the shunt capacitor, problems arise such as increase of factors to process variations and increase of a phase shift error. Accordingly, frequency characteristics need to be sacrificed to some extent in case of the HPFLPF switching type of phase shifter having a small phase shift amount for the high frequency band. 
         [0019]    Meanwhile, in case of the switched line type of phase shifter, a large difference in the line length is required for a large phase shift amount. Accordingly, there are drawbacks such as arrangement of a long transmission line and an increased chip size. As a result, the cost increases. An influence of the larger line difference on frequency characteristics of a phase shifter increases. 
         [0020]    The above problems are caused in both the HPFLPF type of phase shifter and the switched line type of phase shifter, when a phase shift amount is set to be 20 to 45 degrees in the frequency band of about 10 to 15 GHz. Therefore, either frequency characteristics or costs are sacrificed in the conventional phase shifters. 
       SUMMARY  
       [0021]    In a first aspect of the present invention, a phase shifter includes a first signal path in which a first unit is disposed to advance a phase of a signal; a second signal path in which a second unit with no shunt capacitor is disposed to change the phase of the signal such that the changed phase is delayed than the advanced phase by the first unit; and a switch section configured to switch between the first signal path and said second signal path. The first unit comprises a filter, and the second unit is a transmission line. 
         [0022]    In another aspect of the present invention, a bit phase shifter includes a plurality of phase shifters. One of the phase shifters includes a first signal path in which a first unit is disposed to advance a phase of a signal; a second signal path in which a second unit with no shunt capacitor is disposed to change the phase of the signal such that the changed phase is delayed than the advanced phase by the first unit; and a switch section configured to switch between the first signal path and said second signal path. 
         [0023]    According to the present invention, the phase shifter with excellent frequency characteristics in high frequencies can be provided, and an inexpensive phase shifter can also be provided. Moreover, various kinds of phase shifters can be fabricated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
           [0025]      FIG. 1  is a configuration diagram of a phase shifter of an HPFLPF switching type; 
           [0026]      FIG. 2  is a configuration diagram of a phase shifter of a switched line type; 
           [0027]      FIG. 3  is a diagram showing a basic configuration of the best mode to carry out the present invention; 
           [0028]      FIG. 4  is a diagram showing a detailed application example of the present embodiment; and 
           [0029]      FIG. 5  is a diagram showing a bit phase shifter including the phase shifter according to the present embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Hereinafter, a phase shifter according to embodiments of the present invention will be described in detail with reference to the attached drawings. 
         [0031]      FIG. 3  shows a basic configuration of the phase shifter according to a first embodiment of the present invention. In the first embodiment, switches  10  and  12  for switching signal paths are provided, and a high pass filter (HPF)  20  is arranged in one of the signal paths and a microstrip transmission line  30  is arranged in the other signal path. 
         [0032]    An operation of the phase shifter according to the present embodiment will be described with reference to  FIG. 3 . In  FIG. 3 , when ON voltages are applied to a control terminal CON 1  and a control terminal CON 3 , and OFF voltages are applied to a control terminal CON 2  and a control terminal CON 4 , an FET F 1  and an FET F 3  are turned on, and an FET F 2  and an FET F 4  are turned off. At this time, a microwave signal is inputted from an input terminal IN 1  and is outputted from an output terminal OUT 1  via the HPF  20 , which includes series-connected capacitors C 1  and C 2  and an inductor L 1 . Meanwhile, when the OFF voltages are applied to the control terminal CON 1  and the control terminal CON 3 , and the ON voltages are applied to the control terminal CON 2  and the control terminal CON 4 , the FET F 1  and the FET F 3  are turned off, and the FET F 2  and the FET F 4  are turned on. At this time, when being inputted from the input terminal IN 1 , the microwave signal is outputted from the output terminal OUT 1  via the transmission line  30 . 
         [0033]    In the present embodiment, the signal path provided with the HPF  20  and the signal path provided with the transmission line  30  are switched by the SPDT switches  10  and  12 . Therefore, a phase difference between these signal paths can be obtained as a phase shift amount. A phase of a signal of a design frequency is advanced in the signal path on the HPF  20  side, while the phase of the signal is delayed by a value corresponding to a line length in the signal path on the transmission line  30  side. If it is designed to advance a phase by 22.5 degrees on the HPF  20  side and to delay a phase by 22.5 degrees on the transmission line  30  side, a total phase shift amount of 45 degrees can be obtained. 
         [0034]    Although a shunt capacitor causes a problem in realizing a small phase shift amount in high frequency band, the shunt capacitor need not to be arranged in the present embodiment, because the low pass filter (LPF) can be omitted in the present embodiment. As a result, even if a phase shifter is configured to obtain a small phase shift amount in a high frequency band, excellent designability and variation property can be attained. It should be noted that the LPF using the shunt capacitor may be used if the phase shift amount is larger. 
         [0035]    The transmission line is used in the present embodiment. The phase shift amount can be obtained as a phase difference between the advanced phase in the HPF and the delayed phase in the transmission line in the present embodiment, while the phase shift amount is obtained as a difference between the delayed phases in the switched line type phase shifter. Accordingly, a line length to obtain a same phase shift amount can be made shorter than that of the switched line type. For example, a transmission line having a length to delay a phase by 55 degrees is required to obtain the phase shift amount of 45 degrees in the switched line type, as described above. On the contrary, in the above example of the present embodiment, the phase shift amount of 45 degrees can be obtained by using a transmission line to delay a phase by 22.5 degrees. In this manner, the line length of the transmission line used in the present embodiment may be less than a half of the line length required to obtain the same phase shift amount in the switched line type. Accordingly, a chip size can be made smaller significantly. 
         [0036]    As described above, a shunt capacitor of a small capacitance is not required in the configuration of a phase shifter of a relatively small phase shift amount in the high frequency band, although the shunt capacitor is difficult to realize and its characteristics are largely influenced through process variations. As a result, the phase shifter with excellent designability and less variation can be fabricated. Moreover, the HPF allows the line length of the used transmission line to be the line length of a transmission line for 22.5 degrees which is about a half of the line length of the transmission line for 55 degrees in the switched line type, so that a miniaturized chip size can be realized. A configuration can be realized with a chip size which is about a half of a chip size of the phase shifter of the conventional switched line type and equivalent to or smaller than that of the HPFLPF switching type. 
         [0037]      FIG. 4  shows the phase shifter according to a second embodiment of the present invention. The phase shifter in  FIG. 4  has an input-side SPDT switch  14 , an HPF  22  provided in a first path, a transmission line  32  provided in a second path, and an output-side SPDT switch  16 . 
         [0038]    The input-side SPDT switch  14  has an FET F 5  connected to the first signal path, and an FET F 6  connected to the second signal path. Inductors  50  and  52  resonate with the FET F 5  and the FET F 6  functioning as capacitors when OFF voltages are applied to gate electrodes, respectively. Control voltages are applied to a control terminal CON 5  and a control terminal CON 7  in a complementary manner. The output-side SPDT switch  16  has an FET F 7  connected to the first signal path and an FET F 8  connected to the second signal path. Inductors  54  and  56  resonate with the FET F 7  and the FET F 8  functioning as capacitors when OFF voltages are applied to the gate electrodes, respectively. Control voltages are applied to the control terminal CON 7  and the control terminal CON 8  in a complementary manner. As shown in  FIG. 4 , the input-side SPDT switch  14  and the output-side SPDT switch  16  are both made to be resonance switches, in which the FETs F 5  to F 5  are connected in parallel with the inductors  50 ,  52 ,  54  and  56  between the drains and the sources, respectively. In order to switch the signal paths, same control voltages are applied to the control terminal CON 5  of the input-side SPDT switch  14  and the control terminal CON 7  of the output-side SPDT switch  16 , while same control voltages are also applied the control terminal CON 6  of the input-side SPDT switch  14  and the control terminal CON 8  of the output-side SPDT switch  16 . 
         [0039]    In  FIG. 4 , the HPF  22  is disposed in the first signal path. The HPF  22  has a capacitor C 3  provided in series and shunt inductors L 2  and L 3  connected to a ground. The HPF  22  shown in  FIG. 4  has a circuit configuration which is slightly different from that of the HPF  20  of  FIG. 3 . Meanwhile, the transmission line  32  is connected to the second signal path. The transmission line  32  is configured to have an open stub  40 . The open stub  40  functions as a characteristic adjustment circuit. The phase shifter of  FIG. 4  is configured to switch the signal path for the HPF and the signal path for the transmission line by the switches in the same manner as the phase shifter of  FIG. 3 . Accordingly, a circuit operation in the phase shifter of  FIG. 4  is similar to that of the phase shifter of  FIG. 3 , in which similar effects can be obtained. 
         [0040]    In addition to the resonance switches shown in FIG,  4 , switches for switching signals such as a switch of a series shunt type and a switch using diodes other than FETs can be applied to the SPDT switch in the present embodiment. The HPF on the signal path may be an HPF to obtain a plurality of phases using variable capacitance elements and variable resistance elements made by FETs and diodes, in addition to the HPF having various combinations of capacitors and inductors. The HPF is sufficient to advance a phase in a design frequency. The transmission line may also be realized by applying a transmission line to delay a phase by a configuration of a distributed constant circuit such as a microstrip line, even if there are a characteristic impedance difference and a shape difference due to stubs. 
         [0041]    As shown in  FIGS. 3 and 4 , the phase shifter according to the embodiments of the present invention is essentially configured of a pair of a filter which is composed of inductors and a capacitor and allows a phase to advance in the design frequency, and a transmission line which is a member other than the filter and allows the phase to delay. Accordingly, various kinds of modifications could be considered in realizing the phase shifter according to the present embodiment in practice. 
         [0042]    The microwave band phase shifter configured to switch between the HPF and the transmission line by the switches has been described above. Moreover, a microwave band phase shifter configured to switch a first HPF and a second HPF by switches can also be considered. In this case, although being not shown, the HPF  20  or  22  may be used instead of the transmission line  30  or  32 . It should be noted that the HPF instead of the transmission line changes the phase of the signal transmitted on the second signal path such that the changed phase is delayed than the advance phase in the first signal path. If a difference is provided between a phase advanced in the first HPF and a phase advanced in the second HPF, a desired phase shift amount can be obtained. Since an LPF is not used, the shunt capacitor is not required, which allows fabrication of the phase shifter with excellent high frequency characteristics. Depending on the design frequency, a phase shifter may be configured to switch between the first LPF and the second LPF by switches, and a phase shifter may be configured to switch the LPF and a transmission line by switches. A phase shifter with a third signal path added to the above phase shifter can also be considered. 
         [0043]      FIG. 5  is a diagram showing a bit phase shifter including the phase shifters according to the present embodiment. In  FIG. 5 , four phase shifters  62 ,  64 ,  66  and  68  having predetermined phase shift amounts are arranged in cascade to constitute a bit phase shifter  60 . For example, it is assumed that the phase shifter  62  has the phase shift amount of 22.5 degrees, the phase shifter  64  has the phase shift amount of 45 degrees, the phase shifter  66  has the phase shift amount of 90 degrees, and the phase shifter  68  has the phase shift amount of 180 degrees. If digital data “1000” is supplied to the bit phase shifter  60  at this time, the phase shifter  62  is allowed to obtain the phase shift amount of 22.5 degrees, and a microwave signal is inputted from an input terminal IN 3  and is outputted from an output terminal OUT 3  to have the phase shift amount of 22.5 degrees. Similarly, if digital data “0100” is supplied, the phase shifter  64  is allowed to obtain the phase shift amount of 45 degrees. If digital data “1100” is supplied, the phase shift amount of 67.5 degrees is obtained as a sum of the phase shift amount of 22.5 degrees by the phase shifter  62  and the phase shift amount of 45 degrees by the phase shifter  64 . 
         [0044]    If digital data “1111” is supplied, the phase shift amount of 337.5 degrees can be obtained as a sum of the phase shift amount of 22.5 degrees by the phase shifter  62 , the phase shift amount of 45 degrees by the phase shifter  64 , the phase shift amount of 90 degrees by the phase shifter  66 , and the phase shift amount of 180 degrees by the phase shifter  68 , 
         [0045]    According to the phase shifter of the present embodiment, problems in the conventional HPFLPF switching type of phase shifter and the switched line type of phase shifter can be solved in case of realizing a specific phase shift amount. Accordingly, an application of the present embodiment is considered to an internal portion of the bit phase shifter  60  which is unable to constitute by the conventional phase shifters. For example, the phase shifter  62  of the present embodiment is made as the phase shifter configured to switch the HPF and the transmission line by the switches, and the remaining phase shifters  64 ,  66  and  68  may be made as phase shifters of the HPFLPF switching type. When the bit phase shifter is fabricated in practice, the phase shifters according to the present embodiment may be applied to the entire phase shifters. That is, the entire phase shifters  62 ,  64 ,  66  and  68  may be the phase shifter according to the present embodiment. 
         [0046]    As described above, in the switching type of microwave band phase shifter to obtain a phase shift amount by switching two signal paths, an HPF is provided in one of the signal paths and a transmission line is provided in the other signal path. Therefore, it is made possible to solve the conventional problems in the HPFLPF switching type of phase shifters and the switched line type of phase shifters, so that a microwave band phase shifter which is inexpensive and has excellent frequency characteristics can be provided. 
         [0047]    Although the inventions has been described above in connection with several preferred embodiments thereof, it will be appreciated by those skilled in the art that those embodiments are provided solely for illustrating the invention, and should not be relied upon to construe the appended claims in a limiting sense.