Abstract:
An electronic equipment includes one or more electronic devices, a cold stage, and a cold insulation member. The one or more electronic devices perform a predetermined operation within a predetermined temperature range. The cold stage cools down the one or more electronic devices to a predetermined operational temperature at which the one or more electronic devices is operable. The phase transition temperature of the cold insulation member is in a range between the predetermined operational temperature and an upper limit of the predetermined temperature range. The cold insulation member is arranged adjacent to the one or more electronic devices, and retains the temperature of the one or more electronic devices within the predetermined temperature range. At least one electronic devices over which the cold insulation member is arranged is partially formed from a material which is in a superconductive state at the predetermined operational temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic equipment, and, more particularly, to an electronic equipment having a device which is cooled down to an extremely low temperature so as to operate in a superconductive state. 
     2. Description of the Related Art 
     In recent years, radio receivers, with a high degree of reception sensitivity, for use at a mobile communications or satellite communications base station are developed. 
     For example, a radio receiver disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H10-126290 employs a superconductor filter. In this radio receiver, a decrease in the loss of filter is achieved, as compared to any other conventional radio receivers. 
     In this radio receiver, a low-noise amplifier which amplifiers a signal output from a filter is operated at a low temperature, thereby to reduce thermal noise. 
     To have a high degree of reception sensitivity, the radio receiver of the above publication includes a cooler which cools down a superconductor filter and the low-noise amplifier to an extremely low temperature. 
     Because a band pass filter is formed from a superconductor filter, the radio receiver exhibits steep attenuation characteristics over a pass band, and the band pass filter is likely to select signals at a predetermined frequency band. 
     In the case where a radio receiver includes a superconductor filter, it is necessary to control the temperature of the band pass filter to be constant. 
     It is because the pass band frequency of the band pass filter is determined based on the inductance of a filter circuit, and the penetration depth of the superconductor having an effect on the inductance changes depending on the temperature of the band pass filter. 
     Hence, there is employed a method for controlling the electric power to be supplied to the cooler, for example, while monitoring the temperature of the band pass filter. 
     While the cooler included in the radio receiver continues to operate for a long period of time, the level of the electric power to be input to the cooler may change as a result of a temporary variation in voltage or a sudden power failure. Besides, the radio receiver, in many cases, is arranged outside building, thus the cooling capacity of the cooler may change as an effect of a sudden variation in the outside temperature. 
     In this case, the problem is that the temperature of the band pass filter changes and its pass band frequency as well, thus the radio receiver does not perform a predetermined operation. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above. It is accordingly an object of the present invention to provide an electronic equipment, which retains a temperature at which the electronic equipment can perform a predetermined operation, and which is not likely to be effected by some kind of temporary disturbance. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided an electronic equipment comprising: 
     one or more electronic devices which are operable within a predetermined temperature range; 
     a cold stage which cools down said one or more electronic devices to such a predetermined operational temperature that said one or more electronic devices can perform a predetermined operation; and 
     a cold insulation member whose phase transition temperature is in a range between the predetermined operational temperature and an upper limit of the predetermined temperature range, and which is arranged adjacent to said electronic device, and whose phase changes so as to retain a temperature of said one or more electronic devices within the predetermined temperature range, and 
     wherein a part of said one or more electronic devices adjacent to said cold insulation member is formed from a material which is in a superconductive state at the predetermined operational temperature. 
     According to the above structure, while the phase of the cold insulation member is changing, the electronic equipment can retain the predetermined temperature at which the electronic device is operable, and a temporary disturbance is not likely to effect the operations of the electronic equipment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings in which: 
     FIG. 1 is a block diagram showing the structure of a radio receiver according to the first embodiment of the present invention; 
     FIG. 2 is a cross sectional view showing the principal components of the radio receiver according to the first embodiment; 
     FIG. 3 is a cross sectional view showing the principal components of a radio receiver according to the second embodiment; 
     FIG. 4 is a cross sectional view showing the principal components of a radio receiver according to the third embodiment; 
     FIG. 5 is a cross sectional view showing the principal components of a radio receiver according to the fourth embodiment; 
     FIG. 6 is a cross sectional view showing the principal components of a radio receiver according to the fifth embodiment; and 
     FIG. 7 is a perspective view showing the lower section of a package taken along a line A-A′ of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. 
     First Embodiment 
     FIG. 1 is a structural diagram showing the structure of a radio receiver  100  according to the first embodiment of the present invention. FIG. 2 is a vertical cross sectional view schematically showing the principal components of the radio receiver  100 . 
     The radio receiver  100  is used at a mobile communications or satellite communications base station, etc., and arranged at the top of an antenna tower, or the like. 
     As shown in FIG. 1, the radio receiver  100  comprises a band pass filter  110 , a package  111 , a cold insulation member  112 , a cover  113 , a low-noise amplifier  120 , a package  121 , a cold stage  130 , a cooler  140  and a heat pipe  150 . 
     The band pass filter  110  is a superconductor filter, and operates in a superconductive state. When the temperature is 58K (Kelvin), the band pass filter  110  is to select any signals at a particular frequency band from input signals. 
     The band pass filter  110  is required to operate within the temperature variation of 0.5K in this case. 
     The band pass filter  110  is made of a copper-oxide superconducting material, such as Y (yttrium), Bi (bismuth), Tl (thallium), Hg (mercury) whose critical temperature is higher than 80K. 
     The band pass filter  110  is contained in the package  111  having the cover  113 . The cold insulation member  112  is inserted between the package  111  and the cover  113 , and adhered to the outer surface of the package  111 . 
     The cold insulation member  112  is one whose phase transition temperature is a degree of temperature at which the band pass filter  110  performs a predetermined operation. The cold insulation member is formed of, for example, KAl (SO 4 ) 2  (12H 2 O). The phase of KAl (SO 4 ) 2  (12H 2 O) changes at a temperature of 58K. 
     In the state where the phase of the cold insulation member  112  changes, the cold insulation member  112  can maintain the phase transition temperature with the transition heat, until the phase completely changes. 
     The low-noise amplifier  120  is made up of a semiconductor device with a compound semiconductor, and contained in the package  121 . The low-noise amplifier  120  is arranged on the cold stage  130  together with the band pass filter  110 , and amplifies signals output from the band pass filter  110  to a desired level. 
     The cold stage  130  is connected to the cooler  140 , and retained to such a temperature (58K) that the band pass filter  110  arranged thereon performs a predetermined operation. 
     The cooler  140  is a Stirling cycle cooler which generates cold, if helium, etc. is expanded. 
     One end of a heat pipe  150  contact the cooler  140 , and the other end thereof is projected from the radio receiver  100 . The heat pipe  150  outputs heat generated by the cooler  140  from a heat output fin  151 . 
     A heat shielding unit  152  comprises the band pass filter  110 , the package  111 , the cold insulation member  112 , the low-noise amplifier  120 , the package  121  and the cold stage  130 , and is insulated from external heat. 
     The radio receiver  100  operates as follows: 
     The cooler  140  cools down the cold stage  130 , and retains the band pass filter  110  on the cold stage  130  at a temperature of 58K. 
     In this state, a signal received by an antenna  160  is input to the band pass filter  110  through a connector  161  and a coaxial cable. 
     When the temperature of the band pass filter  110  is 58K, the band pass filter  110  selects any signal at a particular frequency band from those input signals, and outputs the selected signal to the low-noise amplifier  120  through a connector  162 . 
     The low-noise amplifier  120  amplifies the signal output from the band pass filter  110  to a desired level and outputs the amplified signal to a received-signal output terminal  164  through a connector  163 . 
     The radio receiver  100  is arranged outside a building, such as at the top of an antenna tower, etc., for example. Hence, the cooling capacity of the cooler  140  may change, if the outside temperature suddenly varies. 
     The cooler  140  continuously operates for a long period of time, for many years. Thus, the level of electric power to be input may change, due to a temporary variation in voltage or a sudden power failure. 
     As described, conventionally, the change in the cooling capacity of the cooler or in the level of the electric power has a direct effect on the conventional radio receiver. Hence, the temperature of the band pass filter varies together with the temperature of the cold stage. 
     For example, when the temperature of the band pass filter raises, the pass band of the band pass filter shifts to a frequency band which is lower than a predetermined frequency band. Thus, the band pass filter can not extract a signal at a desired frequency. 
     The change in the cooling capacity of the cooler or in the level of the electric power does not have much effect on the radio receiver of this embodiment, as follows: 
     For example, when the level of the electric power to be input to the cooler  140  decreases, the temperature of the cold stage  130  connected to the cooler  140  raises, and the temperature of the package  111  on the cold stage  130  also raises. 
     The phase of the cold insulation member  112  adhered to the package  111  begins to shift, when heat absorption is performed by the cold insulation member  112 . While the phase transition state of the cold insulation member  112  is still in the process of changing, the temperature thereof does not vary. 
     Thus, the phase of the cold insulation member  112  completely changes, the temperature of the package  111  in contact with the cold insulation member  112  and the temperature of the band pass filter  110  contained in the package  111  are retained constant. 
     Further, before the phase of the cold insulation member  112  completely changes, if the electric power to be input to the cooler  140  recovers to a predetermined level and the temperature of the cold stage  130  returns to a temperature of 58K, the temperature of the band pass filter  110  stays 58K. 
     In the above circumstances, the frequency characteristics of the band pass filter  110  do not change, therefore, the radio receiver  100  can continuously perform a predetermined operation. 
     Second Embodiment 
     FIG. 3 is a cross sectional view showing the principal components of a radio receiver according to the second embodiment of the present invention. 
     The radio receiver of the second embodiment has substantially the same structure as that of the radio receiver of the first embodiment. The only the difference is that another cold insulation member is arranged on the outer surface of the package including the low-noise amplifier, in the structure of the radio receiver of the second embodiment. 
     Thus, the same component elements are denoted by the same reference numerals, and only differences between the radio receiver of the first and second embodiment will be explained. 
     As shown in FIG. 3, the low-noise amplifier  120  is contained in the package  121  having a cover  123 . The cold insulation member  112  is inserted between the package  121  and the cover  123  and adhered to the outer surface of the package  121 . 
     In a radio receiver  200  of this embodiment, when the cooling capacity of the cooler  140  changes or when the level of the electric power to be input changes, the phase of the cold insulation member  112  changes. 
     When the phase of the cold insulation member  112  is still in the process of changing, the temperature of the cold insulation member  112  does not change. Thus, the temperature of the package  121  and the temperature of the low-noise amplifier  120  in the package  121  are retained constant. 
     Hence, in the radio receiver  200 , when the capacity of the cooler  140  changes or the level of input power changes, the low-noise amplifier  120  reduces a thermal noise occurring in the band pass filter  110 , and can continuously perform an operation for amplifying a signal output from the band pass filter. 
     Third Embodiment 
     FIG. 4 is a cross sectional view showing the principal components of a radio receiver according to the third embodiment of the present invention. 
     The radio receiver of the third embodiment has substantially the same structure as that of the radio receiver of the second embodiment. The only the difference is that another cold insulation member is arranged on the outer surface of the cold stage, in the structure of the radio receiver of the third embodiment. 
     Thus, the same component elements are denoted by the same reference numerals, and only differences between the radio receiver of the second and third embodiments will be explained. 
     As illustrated in FIG. 4, the cold stage  130  includes a cover  133 . The cold insulation member  112  is inserted between the cold stage  130  and the cover  133 . 
     In a radio receiver  300  of this embodiment, when the cooling capacity of the cooler  140  changes or the level of input power changes, the phase of the cold insulation member  112  changes. 
     While the phase of the cold insulation member  112  is still in process of changing, the temperature of the cold insulation member  112  does not vary, hence, the temperatures of the package  111 , package  112  and cold stage  130  are retained constant for a while. 
     The volume of the cold stage  130  is larger than the volume of the packages  111  and  121 , and the thermal capacity of the cold stage  130  is also larger than that of the packages  111  and  121 . 
     Thus, the temperature of the band pass filter  110  is retained constant for a longer period of time than the period of time the temperature of the band pass filter  110  in the radio receiver of the first and second embodiments is retained constant. 
     In this structure, the frequency characteristics of the band pass filter  110  do not change. Hence, the radio receiver  300  can continuously perform a predetermined operation. 
     Fourth Embodiment 
     In the third embodiment, when the cooling capacity of the cooler or the level of the electric power to be input to the cooler changes, the temperature of the band pass filter is retained constant for a long period time. In this structure, the cold insulation member is used a lot, and the radio receiver is made large in size. Now, explanations will be made to a radio receiver, according to the fourth embodiment, which is light in weight and formed in small. 
     FIG. 5 is a cross sectional view showing the principal components of the radio receiver according to the fourth embodiment of the present invention. The same component elements are denoted by the same reference numerals as those of the elements included in the radio receiver of the first embodiment. 
     In a radio receiver  400 , as shown in FIG. 5, the band pass filter  110  and the low-noise amplifier  120  are integrated with each other and contained in a single package  401 . 
     The band pass filter  110  and the low-noise amplifier  120  are connected with each other through a bonding wire  402 . 
     The package  401  is covered by a cover  413 . A cold insulation member  412  is hermetically inserted between the package  401  and the cover  413 , and is adhered to the outer surface of the package  401 . 
     The cold insulation member  412  is formed of KCN whose phase transition temperature is 83K. 
     The band pass filter  110  operates at 83K at a certain frequency as a pass band. 
     When the cooling capacity of the cooler  140  or the level of the electric power to be input to the cooler  140  changes, the temperatures of the band pass filter  110  and low-noise amplifier  120  are respectively retained constant, until the phase of the cold insulation member  412  completely changes. 
     In this embodiment, no connector connecting the band pass filter  110  and the low-noise amplifier  120  is necessary. Hence, as compared to the radio receiver according to any one of the first to third embodiments, the radio receiver of this embodiment can be light in weight and formed small in size. 
     A modification may be made to the radio receiver of the fourth embodiment, by arranging the cold insulation member on the outer surface of the cold stage. When the cooling capacity of the cooler changes or the level of the electric power to be input to the cooler changes, the radio receiver of the modification can stably operate for a longer period of time than the period of time the radio receiver of the fourth embodiment can operate. 
     Fifth Embodiment 
     FIG. 6 is a cross sectional view showing the principal elements of a radio receiver according to the fifth embodiment of the present invention. 
     FIG. 7 is a perspective view of a lower section  513  of a package  511  taken along a line A-A′ of FIG.  6 . 
     A radio receiver  500  has basically the same structure as that of the first embodiment, as shown in FIG. 6, and the same component elements are denoted by the same reference numerals. 
     The difference in the structures of the first embodiment and the fifth embodiment is that a cold insulation member  512  is contained in a space  514  arranged inside the package  511 , instead of being arranged on the outer surface of the package  511 . 
     The lower section  513  of the package  511  includes a space  514  and a plurality of pillars  515 . The plurality of pillars  515  are arranged at equal intervals in the space  514 , as shown in FIG.  7 . 
     The cold insulation member  512  is formed of N 2  in the form of a solid body which melts at a temperature of 63K so as to be liquified. 
     The band pass filter  110  operates at a temperature of 63K at a predetermined frequency band as a pass band. 
     The cold insulation member  512  is inserted in the space  514  in the package  511 . After the phase of the cold insulation member  512  changes, the cold insulation, member  512  is liquified, and uniformly flows through the pillars  515 . 
     In this structure, the cold insulation member  512  can uniformly transfer heat onto the band pass filter  110 . 
     When the cooling capacity of the cooler  140  changes or the level of the electric power to be input to the cooler  140  changes, the temperature of the band pass filter  110  can be retained the same during the phase transition of the cold insulation member  512 . 
     If the cold insulation member  512  is contained in the space of the package  121  of the low-noise amplifier  120  and the cold stage  130 , the temperature of the band pass filter  110  can be retained the same for a longer period of time than the phase transition of the cold insulation member  512 . 
     The cold insulation member  512  can be arranged on the outer surface of the package  511 , package  121  and cold stage  130 . 
     The preferred embodiments of the present invention have explained. However, the present invention is not limited to the above embodiments, and can be applied to a radio transmitter or a radio transceiver, and also to a general electronic device which operates at an extremely low temperature. 
     Various embodiments and changes may be made thereonto without departing from the broad spirit and scope of the invention. The above-described embodiments are intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiment. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention. 
     This application is based on Japanese Patent Application No. H11-356792 filed on Dec. 16, 1999, and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.