Patent Publication Number: US-2005128025-A1

Title: Ultralow temperature low noise amplification apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to an ultralow-temperature low-noise amplification apparatus having a first-stage amplifier and a final-stage amplifier cooled to a very low temperature between an input connector and an output connector.  
      2. Description of the Related Art  
       FIG. 6  is a block diagram showing in a simplified form the layout of a known highly sensitive amplification apparatus used in e.g., a wireless communication system. In the highly sensitive amplification apparatus  61 , input signals applied to an input connector  131  are amplified by a first-stage amplifier  111  and delivered to a final-stage amplifier  121 . The amplified signals received by the final-stage amplifier  121  are further amplified and outputted through an output connector  141 . Power is supplied to the first- and final-stage amplifiers  111  and  121  through a power supply connector  151 . If an amplifying element having a low noise figure is selected as a principal component of each of the first- and final stage amplifiers  111  and  121 , it is possible to improve the noise figure of each amplifier and thereby the high sensitivity of the highly sensitive amplification apparatus as a whole.  
      The noise figure is an important factor for the evaluation of a highly sensitive amplification apparatus and is desirably as small as possible, and a HEMT (high electron mobility transistor) is, for example, used as a low-noise amplifying element for the microwave frequency range. Even if a low-noise amplifying element, such as a HEMT, may be used, however, its noise figure depends on the frequency range of the input signals to be amplified, and a problem in which no desired noise figure cannot be obtained would be raised, depending on their frequency range. On the other hand, it is known that an amplifying element generally has a smaller noise figure when used at a low temperature than at a high temperature. Therefore, there has already been proposed a cooled highly sensitive amplification apparatus in which an amplifying element is cooled to realize a noise figure suited for a highly sensitive amplification apparatus.  
       FIG. 7  is a block diagram showing in a simplified form the layout of a known low-temperature low-noise amplification apparatus comprising a cooled highly sensitive amplification apparatus as mentioned above. In the low-temperature low-noise amplification apparatus  62 , amplifiers  111  and  121  supplied with power from a power supply connector  151  amplify input signals applied to an input connector  131  and send amplified signals to an output connector  141 . Accordingly, its function is equal to that of the highly sensitive amplification apparatus  61  shown in  FIG. 6 . The apparatus shown in  FIG. 7 , however, includes a low temperature holder  172  cooled by a freezer  173  and positioned in contact with the amplifiers  111  and  121 . The amplifiers  111  and  121 , the low temperature holder  172  and those parts of the connectors  131 ,  141  and  151  which face the amplifiers are held in a tightly closed heat-insulating container  171 , its interior of which is maintained vacuum by an evacuator not shown. Therefore, the interior of the heat-insulating container  171  including the low temperature holder  172  is steadily kept at a low temperature.  
      Although in the apparatus described above, it is only the amplifiers that are installed inside for signal processing, a highly sensitive amplification apparatus for processing high-frequency signals sometimes has a receive filter formed from a high-temperature superconductor. A high-temperature superconductor, such as an oxide superconductor, exhibits superconductivity at or below a critical temperature of about 70 K. If a receive filter formed from such a superconductor is combined with a low-temperature low-noise amplification apparatus and if all the necessary parts including the receive filter are kept at or below the critical temperature, it is possible to realize a great reduction of any loss caused by the receive filter, etc. and thereby a drastic improvement in the noise figure of the apparatus as a whole.  
       FIG. 8  is a block diagram showing a known ultralow-temperature low-noise amplification apparatus made by combining a low-temperature low-noise amplification apparatus and a receive filter formed from a high-temperature superconductor as stated above. The ultralow-temperature low-noise amplification apparatus  63  is made by interposing a superconducting filter  110  between the first-stage amplifier  111  and input connector  131  in the low-temperature low-noise amplification apparatus  62  shown in  FIG. 7 . The superconducting filter  110 , as well as the first- and final-stage amplifiers  111  and  121 , is positioned in contact with a low temperature holder  172  and cooled to a predetermined temperature equal to or below the critical temperature.  
      In the apparatus shown in  FIG. 8 , high-frequency signals applied to the input connector  131  pass through a high-frequency cable  132 , and the signals in a pass band of frequencies are allowed to pass through the superconducting filter  110  and pass through a high-frequency cable  133  to the first-stage amplifier  111  whereby they are amplified. The high-frequency signals amplified by the first-stage amplifier  111  pass through a high-frequency cable  143  and are amplified by the final-stage amplifier  121  and the amplified signals pass through a high-frequency cable  142  and are outputted through an output connector  141 . Accordingly, the radio amplification apparatus  63  shown in  FIG. 8  is substantially the same in performance as the low-temperature low-noise amplification apparatus  62  shown in  FIG. 7 , except that the inputted high-frequency signals are filtered by the superconducting filter  110 .  
      For the proper operation of the radio amplification apparatus  63  shown in  FIG. 8 , it is necessary to have the freezer  173  cool and hold various parts of the ultralow-temperature low-noise amplification apparatus  63  steadily at or below the critical temperature and it is, therefore, important to keep the freezer  173  reliable in performance. An increase in the amount of heat entering the heat-insulating container  171  calls for a higher freezing power and results in a cost increase caused by the necessity for a larger and heavier freezer and a greater electric power consumption.  
     SUMMARY OF THE INVENTION  
      Under these circumstances, it is an object of this invention to provide an ultralow-temperature low-noise amplification apparatus of high sensitivity which realizes a small size, a light weight, a low electric power consumption and a low price.  
      According to one aspect of this invention, the above object is attained by an ultralow-temperature low-noise amplification apparatus having a first-stage amplifier and a final-stage amplifier which are cooled to a very low temperature between an input connector and an output connector, the apparatus further comprising an input connecting device connecting the input connector and the first-stage amplifier and so arranged as to reduce any insertion loss and an output connecting device connecting the final-stage amplifier and the output connector and so arranged as to reduce the conduction of heat.  
      According to another aspect of this invention, there is provided an ultralow-temperature low-noise amplification apparatus comprising a first signal transmitting device connecting an input connector and a receive filter, a second signal transmitting device connecting the receive filter and a first-stage amplifier, a third signal transmitting device connecting the first-stage amplifier and a final-stage amplifier, a fourth signal transmitting device connecting the final-stage amplifier and an output connector, a cooling holder for cooling the receive filter, second signal transmitting device, first-stage amplifier, third signal transmitting device and final-stage amplifier to a very low temperature and holding them at that temperature, and a heat-insulating container carrying the input and output connectors and a power supply connector on its outer wall and enclosing the second signal transmitting device, first-stage amplifier, third signal transmitting device, final-stage amplifier and cooling holder tightly in a vacuum state.  
      The first signal transmitting device is preferably of a material of low resistivity.  
      The receive filter, second and third signal transmitting devices, and final-stage amplifier preferably constitute a single module.  
      According to still another aspect of this invention, there is provided an ultralow-temperature low-noise amplification apparatus comprising a receive filter connected to an input connector, a first signal transmitting device connecting the receive filter and a first-stage amplifier, a second signal transmitting device connecting the first-stage amplifier and a final-stage amplifier, a third signal transmitting device connecting the final-stage amplifier and an output connector, a cooling holder for cooling the receive filter, first signal transmitting device, first-stage amplifier, second signal transmitting device and final-stage amplifier to a very low temperature and holding them at that temperature, and a heat-insulating container carrying the input and output connectors and a power supply connector on its outer wall and enclosing the receive filter, first signal transmitting device, first-stage amplifier, second signal transmitting device, final-stage amplifier and cooling holder tightly in a vacuum state.  
      The receive filter, first and second signal transmitting devices, and final-stage amplifier preferably constitute a single module.  
      The insertion loss caused by the first signal transmitting device positioned before the first-stage amplifier is the most responsible for any increase in the noise figure of the ultralow-temperature low-noise amplification apparatus as a whole. Therefore, the first signal transmitting device is formed from a material causing only a small insertion loss to reduce the noise figure of the whole apparatus effectively. The third signal transmitting device not substantially affecting the noise figure of the apparatus is formed from a material of low thermal conductivity, so that it may be possible to prevent any external heat from entering the heat-insulating container through the output connector, keep the interior of the heat-insulating container steadily at a low temperature and thereby maintain a low noise figure for the apparatus.  
      According to the present invention, the use of adequate materials for the first signal transmitting device on the input side of the apparatus and the third signal transmitting device on the output side as stated above makes it possible to provide an ultralow-temperature and low-noise amplification apparatus of high sensitivity which has an improved noise figure, does not call for any cooling device having a very high cooling capacity, but realizes a small size, a light weight, a low electric power consumption and a low price.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram for explaining the principle of this invention;  
       FIG. 2  is another block diagram for explaining the principle of this invention;  
       FIG. 3  is a block diagram showing a first form of ultralow-temperature low-noise amplification apparatus embodying this invention;  
       FIG. 4  is a block diagram showing a second form of ultralow-temperature low-noise amplification apparatus embodying this invention;  
       FIG. 5  is a block diagram showing a third form of ultralow-temperature low-noise amplification apparatus embodying this invention;  
       FIG. 6  is a block diagram showing in a simplified form the layout of a known highly sensitive amplification apparatus used in e.g., a wireless communication system;  
       FIG. 7  is a block diagram showing in a simplified form the layout of a known low-temperature low-noise amplification apparatus constituted by a cooled highly sensitive amplification apparatus; and  
       FIG. 8  is a block diagram showing a known ultralow-temperature low-noise amplification apparatus made by combining the low-temperature low-noise amplification apparatus shown in  FIG. 7  and a receive filter formed from a high-temperature superconductor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Description will now be made of several modes of embodying this invention with reference to the drawings.  FIGS. 1 and 2  are block diagrams for explaining the principle of this invention,  FIG. 3  is a block diagram showing a first form of ultralow-temperature low-noise amplification apparatus embodying this invention,  FIG. 4  is a block diagram showing a second form of ultralow-temperature low-noise amplification apparatus embodying this invention and  FIG. 5  is a block diagram showing a third form of ultralow-temperature low-noise amplification apparatus embodying this invention.  
      Description will first be made of the principle on which the ultralow-temperature low-noise amplification apparatus of high sensitivity according to this invention is based. Assumed that an ultralow-temperature low-noise amplification apparatus is made with the same layout as the ultralow-temperature low-noise amplification apparatus  63  shown in  FIG. 8 , and that measures are taken to reduce the amount of heat entering the heat-insulating container  171  and maintain a low noise figure. Let it be assumed that the two-stage amplification apparatus has a first-stage amplifying device M 1  having a gain G 1  and a noise figure F 1  and a final-stage amplifying device M 2  having a gain G 2  and a noise figure F 2  between an input connector  131  and an output connector  141 , as shown in  FIG. 1 . Let it be assumed that the amplification apparatus shown in  FIG. 1  has a gain G and a noise figure F as a whole. The noise figure F of the amplification apparatus shown in  FIG. 1  is expressed by the following formula (1): 
 
 F=F   1 +( F   2 −1)/ G   1   (1) 
 
      The formula (1) teaches that it is only the noise figure F 1  of the first-stage amplifying device M 1  that greatly affects the noise figure F of the two-stage amplification apparatus, while it is hardly affected by the noise figure F 2  of the final-stage amplifying device M 2 . In other words, it can be said that the noise figure of the amplification apparatus as a whole is greatly affected by the noise figure of the first-stage amplifying device, and is less affected by the noise figure of the final-stage amplifying device as the first-stage amplifying device has a higher gain. Accordingly, it is desirable to design the amplifier on the input side with a high gain and a low noise figure and reduce as much as possible any loss caused before the input to the first-stage amplifying device M 1 , while the noise figure of the final-stage amplifying device M 2  on the output side exerts a less effect as there is a higher gain on the input side.  
      If only the gain, loss and noise figure are taken up in respect of the ultralow-temperature low-noise amplification apparatus  63  shown in  FIG. 8  and are expressed as being equivalent, there is obtained a block diagram represented as  FIG. 2 . An attenuator T 1  represents a combination of the high-frequency cable  132 , superconducting filter  110  and high-frequency cable  133  shown in  FIG. 8  (first signal transmitting device). An attenuator T 2  represents the high-frequency cable  143  (second signal transmitting device). An attenuator T 3  represents the high-frequency cable  142  (third signal transmitting device). In view of the description of  FIG. 1  and the representation of  FIG. 2  teaching that it is the loss caused by the attenuator T 1  and the noise figure of the first-stage amplifier  111  that exert a large effect directly on the noise figure of the amplification apparatus as a whole, while the superconducting filter  110  causes only a small loss owing to its properties as a superconductor, the apparatus has a very high noise figure if the high-frequency cables  132  and  133  cause a large loss. The characteristics of the apparatus after the first-stage amplifier  111  are considered as exerting a less effect on its noise figure as the first-stage amplifier  111  has a higher gain.  
       FIG. 3  is a block diagram showing a first form of ultralow-temperature low-noise amplification apparatus as constructed in accordance with the principle described above. In the ultralow-temperature low-noise amplification apparatus  1  shown in  FIG. 3 , high-frequency signals applied to an input connector  31  pass through a high-frequency cable  32 , are filtered through a superconducting filter  10  and are delivered through a high-frequency cable  33  to a first-stage amplifier  11 . Cables made of copper, or like material of low resistivity (which causes only a small insertion loss), such as semi-rigid cables, are used as the high-frequency cables  32  and  33 . On the input side, it is more important to realize a low noise figure than to avoid the infiltration of heat from outside. In this connection, it is desirable to use cables having as large a cross-sectional area as possible to lower the resistivity of the high-frequency cables  32  and  33  as much as possible.  
      The high-frequency signals amplified by the first-stage amplifier  11  are delivered to a final-stage amplifier  2  through a high-frequency cable  43  and the high-frequency signals amplified by the final-stage amplifier  21  are sent through a high-frequency cable  42  and outputted through an output connector  41 . Referring to the high-frequency cables, a cable formed from molybdenum having a low thermal conductivity is used as the high-frequency cable  42 . This makes it possible to prevent any external heat from entering through the output connector  41 . The high-frequency cable  43  may be a cable of any adequate material, but is preferably of a material of low resistivity. A low temperature holder  72  is cooled by a freezer  73 , while it is positioned in contact with the superconducting filter  10  and the amplifiers  11  and  21 .  
      A heat-insulating container  71  carrying the input and output connectors  31  and  41  and a power supply connector  51  on its sidewalls, etc. and minimizing the infiltration of any external heat encloses the high-frequency cables  32 ,  33 ,  43  and  42 , the superconducting filter  10  and the amplifiers  11  and  21  tightly and shuts off the infiltration of any external heat. The heat-insulating container  71  has its interior kept vacuum by an evacuator not shown. Accordingly, the interior of the heat-insulating container  71  including the low temperature holder  72  cooled by the freezer  73  is steadily kept at a low temperature. The following is a comparison of characteristics between copper and molybdenum mentioned above as the materials for the high-frequency cables  32  and  33  and the high-frequency cable  42 , respectively:  
     Thermal Conductivity Electrical Resistivity  
     
         
         
           
              (1) Copper 403 κ/(W·m −1 ·K −1 ) 1.55 ρ/(Ω.m)  
              (2) Molybdenum 139 κ/(W·m −1 ·K −1 ) 5.00 ρ/(Ω.m) 
 
 from which it is obvious that the selection of the materials for the high-frequency cables is proper as intended, since copper used for the cables on the input side is low in electrical resistivity, while molybdenum for the output side is low in thermal conductivity. 
 
           
         
       
    
       FIG. 4  is a block diagram showing a second form of ultralow-temperature low-noise amplification apparatus embodying this invention. The ultralow-temperature low-noise amplification apparatus  2  is substantially of the same construction as the ultralow-temperature low-noise amplification apparatus  1  shown in  FIG. 3 , and differs therefrom only in that high-frequency signals applied to the input connector  31  are so arranged as to be delivered to the superconducting filter  10  directly without passing through any high-frequency cable  32 . The direct connection of the input connector  31  and the superconducting filter  10  makes it possible to reduce any loss otherwise caused by the high-frequency cable  32  and thereby improve the noise figure of the ultralow-temperature low-noise amplification apparatus as a whole.  
       FIG. 5  is a block diagram showing a third form of ultralow-temperature low-noise amplification apparatus embodying this invention. The ultralow-temperature low-noise amplification apparatus  3  is substantially of the same construction as the ultralow-temperature low-noise amplification apparatus  1  shown in  FIG. 3 , and differs therefrom only in that the superconducting filter  10  and the amplifiers  11  and  21  are combined to constitute a low-noise amplifying module  79 . The combination of the superconducting filter  10  and the amplifiers  11  and  21  into the low-noise amplifying module  79  makes unnecessary the high-frequency cables  33  and  43  used in the apparatus of  FIG. 3  and permits a corresponding reduction in any insertion loss. Micro-strip lines can, for example, be used to provide connections making up for the high-frequency cables  33  and  43 . A high-temperature superconductor is preferably used as the material for those connections.  
      Although attention has been drawn only to the materials for the high-frequency cables in the foregoing description, it is possible to employ a device allowing for electrical connection, while cutting off any physical connection (a coupling condenser), since the signals to be processed are of an alternating current. It is also possible to use a long high-frequency cable on the output side of the apparatus. The same is applicable to any amplification apparatus not having any superconducting filter, though the foregoing description has been only of examples of apparatus having a superconducting filter. Moreover, it is needless to say that while those examples have all been of apparatus having two amplifiers, the same principle is applicable to any apparatus having more than two amplifiers.