Abstract:
A low-noise amplifier which is equipped with at least one redundancy circuit which is connected in parallel to an amplifying circuit, so that the low-noise amplifier operates without a significant signal loss even when an abnormality takes place in the amplifying circuit and the amplifying circuit is not replaced or troubleshooted. The low-noise amplifier includes a redundancy circuit ( 30 ) effectively operable instead of an amplifying circuit ( 24 ) when the amplifying circuit ( 24 ) is in an abnormal condition, and at least one switch ( 22 ) activates the redundancy circuit ( 30 ) when the amplifying circuit ( 24 ) is abnormal. In a preferred embodiment, the redundancy circuit ( 30 ) includes a transmission line ( 32 ) for bypassing an input RF signal when the amplifying circuit ( 24 ) is in an abnormal condition. In an alternative, the redundancy circuit ( 30 ) includes a redundant amplifying circuit ( 34 ), so that the redundant amplifying circuit ( 34 ) can amplify the input RF signal in place of the amplifying circuit ( 24 ).

Description:
Hereby incorporated by reference are Korean priority applications 1998-21613, 1998-27169 and 1999-8688. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an amplifier circuit, and more particularly, to a low-noise amplifier circuit typically used for a wireless communications equipment. 
     2. Description of the Related Art 
     In a radio frequency (RF) signal receiving apparatus such as a cellular phone and a base station of a wireless communication system, a received signal has very weak intensity and includes considerable noise mixed therein. Accordingly, such a signal receiving apparatus requires a circuit for amplifying the received signal while reducing a noise figure of the signal. A low-noise amplifier, which is typically installed in an input stage of the signal receiving apparatus, amplifies the input RF signal so that an amplified signal has a required gain and noise figure. 
     As illustrated in FIG. 1, a conventional low-noise amplifier  10  includes an amplifying circuit  14  performing an amplification of the RF signal and impedance matching circuits  12  and  16  for matching impedances between the amplifying circuit  14  and external circuits. The input and output impedance matching circuits  12  and  16  are designed based on scattering parameters (S-parameters) so that reflection coefficients are minimized at input and output stages of the amplifier. Meanwhile, since the low-noise amplifier determines the overall noise characteristics of the signal receiving apparatus, the amplifier is usually designed in a balanced type rather than a single-ended type so as to have a minimum noise figure. 
     As shown in FIG. 2, a balanced type low-noise amplifier includes at least one amplifying stage, a power supply for providing DC power to the amplifying stage, hybrid couplers for splitting or combining signals at input and output stages, delay compensating circuits for compensating phase difference between the signal paths existing between the hybrid couplers, a noise removing circuit for reducing noise, and a comparator for comparing a signal or a supply voltage with a reference. In particular, the power supply can be implemented in various manners to procure an optimum amplification. 
     If any one of the internal circuits of the amplifying circuit happens to be damaged or the supply voltage is lost, the amplifying circuit cannot operate properly. In such a case, the signal receiving apparatus or the overall communication system happens to be faced with a significant signal loss. Meanwhile, when the low-noise amplifier cannot operate normally, the comparator in the amplifying circuit may detect the abnormality to notify a user via a light emitting diode so that the user replaces or troubleshoots the amplifying circuit. However, in a critical situation, the system may be inoperable at all until the user or a maintenance personnel replaces or troubleshoots the amplifying circuit. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a low-noise amplifier which is equipped with at least one redundancy circuit which is connected in parallel to an amplifying circuit, so that the low-noise amplifier operates without a significant signal loss even when an abnormality takes place in the amplifying circuit and the amplifying circuit is not replaced or troubleshooted yet. 
     In order to achieve the above object, a low-noise amplifier according to the present invention includes a redundancy circuit effectively operable instead of an amplifying circuit when the amplifying circuit is in an abnormal condition, and at least one switch for activating the redundancy circuit when the amplifying circuit is abnormal. In a preferred embodiment, the redundancy circuit includes a transmission line for bypassing an input RF signal when the amplifying circuit is in an abnormal condition. In an alternative, the redundancy circuit includes a redundant amplifying circuit, so that the redundant amplifying circuit amplifies the input RF signal in place of the amplifying circuit. 
     According to the present invention, the low-noise amplifier is operable without a significant signal loss when the main amplifying circuit has an abnormality and cannot operate effectively. Thus, it is possible to prevent the communication system employing the circuit from being inoperable even when any one of the internal circuits of the amplifying circuit happens to be damaged or the supply voltage is lost. Accordingly, the reliabilities of the low-noise amplifier and the communication system are enhanced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a block diagram of a conventional low-noise amplifier; 
     FIG. 2 is a detailed block diagram of the amplifying circuit in the low-noise amplifier of FIG. 1; 
     FIG. 3 is a block diagram of an embodiment of the low-noise amplifier according to the present invention; 
     FIG. 4 is a detailed block diagram of an embodiment of the first switch shown in FIG. 3; 
     FIG. 5 is a detailed block diagram of another embodiment of the first switch shown in FIG. 3; 
     FIG. 6 is a block diagram of another embodiment of the low-noise amplifier according to the present invention; 
     FIG. 7 is a block diagram of still another embodiment of the low-noise amplifier according to the present invention; and 
     FIG. 8 is a block diagram of yet still another embodiment of the low-noise amplifier according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A low-noise amplifier of FIG. 3, which amplifies a RF signal from a not shown RF signal source to provide an amplified signal to a not shown signal processing circuit, includes an input impedance matching circuit  20 , a first switch  22 , a first amplifying circuit  24 , a redundancy circuit  30 , a second switch  38 , an output impedance matching circuit  40 , and a control signal generator  42 . 
     The input impedance matching circuit  20  matches an amplifier impedance at the input stage of the amplifier to the impedance of a transmission line connecting the RF signal source and the amplifier, so that the reflection of the RF signal at the input stage is minimized. The output impedance matching circuit  40  matches an amplifier impedance at the output stage of the amplifier to the impedance of a transmission line connecting the amplifier and the signal processing circuit, so that the reflection of the amplified signal at the output stage is minimized. 
     The input node  22   a  of the first switch  22  is connected to the output terminal of the input impedance matching circuit  20 . Two output nodes  22   b  and  22   c  of the first switch  22  are connected to the input terminals of the first amplifying circuit  24  and the redundancy circuit  30 , respectively. The input node  22   a  of the first switch  22  is electrically connected to either the first output node  22   b  or the second output node  22   c  in response to a switching control signal. Accordingly, the first switch  22  provides a signal from the matching circuit  20  to either the first amplifying circuit  24  or the redundancy circuit  30  according to the switching control signal. 
     In the preferred embodiment, the switching control signal may have two logic levels, i.e., a HIGH level and a LOW level. When the first amplifying circuit  24  operates normally, the switching control signal is at the HIGH level and the signal from the matching circuit  20  is provided to the first amplifying circuit  24 . When the first amplifying circuit  24  is in an abnormal condition, however, the switching control signal is at the LOW level and the signal from the matching circuit  20  is provided to the redundancy circuit  30 . The configuration of the first switch  22  will be described in detail below. 
     The first amplifying circuit  24  includes at least one amplifying stage  26  biased by a biasing circuit  28 . The amplifying stage  26  amplifies the signal provided by the first switch  22 . The first amplifying circuit  24  may be implemented by employing the conventional circuit of FIG. 2, for example. Meanwhile, the redundancy circuit  30  is implemented by use of a micro strip transmission line  32  having an impedance of 50 Ω. The width, length, and material of the micro strip  32  are designed based on a wavelength of the required frequency. The micro strip  32  functions as a low-loss signal path while the first amplifying circuit cannot operate normally. 
     Two input nodes  38   a  and  38   b  of the second switch  38  are connected to the output terminals of the first amplifying circuit  24  and the redundancy circuit  30 , respectively. The output node  38   c  of the second switch  38  is connected to the input terminal of the output impedance matching circuit  40 . The output node  38   c  of the second switch  38  is electrically connected to the first input node  38   a  or the second input node  38   b  in response to the switching control signal. Accordingly, the second switch  38  selects either the output of the first amplifying circuit  24  or that of the redundancy circuit  30  according to the switching control signal, and outputs the selected signal to the output impedance matching circuit  40 . The second switch  38  may be configured in a manner similar to the first switch  22 . 
     The control signal generator  42  monitors the operation status of the first amplifying circuit  24  and generates the switching control signal, of which level changes based on the monitored result. In the preferred embodiment, the control signal generator  42  monitors the normality of the biasing voltage Vb provided by the biasing circuit  28  to the amplifying stage  26  to change the level of the switching control signal. If the biasing voltage Vb is within a preset range, the control signal generator  42  outputs the switching control signal of HIGH level. If the biasing is voltage Vb deviates from the preset range, however, the control signal generator  42  outputs the switching control signal of LOW level. 
     Alternatively, the control signal generator  42  may detect the current or voltage level of the output signal of the matching circuit  20  in addition to the biasing voltage Vb to reflect the current or voltage level in determining the level of the switching control signal. In such a case, the switching control signal will be at HIGH level when both the biasing voltage Vb and the current or voltage level are within respective preset ranges, but at LOW level when the biasing voltage Vb or the current or voltage level deviates from the respective preset range. 
     In FIG. 3, a status indicator  44  indicates the operation status of the low-noise amplifier. For example, the status indicator  44  may include light emitting diodes showing which path of the first amplifying circuit  24  and the redundancy circuit  30  is effectively operative. Thus, a maintenance personnel may easily grasp the abnormality of the first amplifying circuit  24  to try the replacement or troubleshooting of the first amplifying circuit  24 . Meanwhile, the maintenance personnel may change the operative path arbitrarily by use of the reset circuit  46 . For example, the personnel may press a reset button to activate the reset circuit  46  upon the completion of the replacement or troubleshooting, so that the first amplifying circuit  24  restarts the effective operation. 
     On the other hand, in the low-noise amplifier according to the present invention, the output signal of either the first amplifying circuit  24  or the redundancy circuit  30  has a zero level at any instant. Considering the feature, any coupling circuit, e.g., a hybrid coupler, may be used instead of the second switch  38  in an alternative of the present embodiment. In such an embodiment, the coupling circuit adds the output signals of the first amplifying circuit  24  and the redundancy circuit  30 , and provides the added signal to the output impedance matching circuit  40 . In this case, it is preferable that a delay-compensating circuit is included in at least one signal path so that the difference in delays in the signal paths is eliminated. 
     FIG. 4 illustrates an embodiment of the first switch  22  shown in FIG. 3 in detail. The first switch of FIG. 4 includes two pin diodes  102  and  106 , and a guiding transmission line  104 . The guiding transmission line  104  has a length of one quarter of the wavelength of the RF signal. An anode of the diode  102  is connected to the input node  22   a , and a cathode thereof is connected to the first output node  22   b . One end of the guiding transmission line  104  is connected to the anode of the diode  102 , and the other end thereof is connected to the second output node  22   c . The diode  106  is connected between ground and the other end of the guiding transmission line  104 . Meanwhile, the switching control signal is provided through the first output node  22   b  in the present embodiment. 
     The first switch of FIG. 4 operates as follows. When the switching control signal is at HIGH level, the diodes  102  and  106  are forward-biased and thus turned on. At this time, most of the signal supplied through the input node  22   a  is transmitted to the first amplifying circuit through the diode  102 . Even though a small portion of the supplied signal may be incident into the guiding transmission line  104 , such a leakage flows into ground via the diode  106 . Meanwhile, when the switching control signal is at LOW level, the diodes  102  and  106  are reverse-biased and thus turned off. At this time, the signal supplied through the input node  22   a  is transmitted to the redundancy circuit  30  through the guiding transmission line  104  and the second output node  22   c.    
     FIG. 5 illustrates another embodiment of the first switch  22  shown in FIG. 3 in detail. The first switch of FIG. 5 includes three pin diodes  112 ,  116 , and  118 , and a guiding transmission line  114 . The guiding transmission line  114  has a length of a half of the wavelength of the RF signal. An anode of the diode  112  is connected to the input node  22   a , and a cathode thereof is connected to the first output node  22   b . One end of the guiding transmission line  114  is connected to the anode of the diode  112 , and the other end thereof is connected to the second output node  22   c . The diode  116  is connected between ground and the other end of the guiding transmission line  114 . The diode  118  is connected between ground and a central position of the guiding transmission line  114 . Meanwhile, the switching control signal is provided through the first output node  22   b  also in the present embodiment. 
     The first switch of FIG. 5 operates as follows. When the switching control signal is at HIGH level, all the diodes  112 , 116 , and  118  are forward-biased and thus turned on. At this time, most of the signal supplied through the input node  22   a  is transmitted to the first amplifying circuit through the diode  112 . Even though a small portion of the supplied signal may be incident into the guiding transmission line  114 , such a leakage flows into ground via the diodes  116  and  118 . Meanwhile, when the switching control signal is at LOW level, all the diodes  112 ,  116 , and  118  are reverse-biased and thus turned off. At this time, the signal supplied through the input node  22   a  is transmitted to the redundancy circuit  30  through the guiding transmission line  114  and the second output node  22   c.    
     FIG. 6 illustrates another embodiment of the low-noise amplifier according to the present invention. The low-noise amplifier of FIG. 6 has a similar configuration to that of FIG. 3 except the redundancy circuit  30 . In FIG. 6, the redundancy circuit  30  includes an amplifying circuit having at least one amplifying stage  34  biased by a biasing circuit  36 . Accordingly, the redundancy circuit  30  can amplify an input signal rather than simply bypassing the input signal. In case that one of two amplifying circuits is inoperable, the other one can perform the amplification of the input signal. Meanwhile, in an alternative of the present embodiment, the biasing circuit  36  in the redundancy circuit  30  may be omitted. In such an embodiment, the amplifying stage  34  may be biased by the biasing circuit  28  in the first amplifying circuit  24 . Since the other features of the low-noise amplifier of FIG. 6 is the same as those of the amplifier of FIG. 3, the detailed description thereof is omitted. 
     FIG. 7 illustrates still another embodiment of the low-noise amplifier according to the present invention. The low-noise amplifier of FIG. 7 includes a first switch  60 , a first amplifying circuit  70 , a redundancy circuit  80 , a second switch  90 , and a control signal generator  92 . 
     The input node  60   a  of the first switch  60  is connected to an external RF signal source. Two output nodes  60   b  and  60   c  of the first switch  60  are connected to the input terminals of the first amplifying circuit  70  and the redundancy circuit  80 , respectively. The input node  60   a  of the first switch  60  is electrically connected to either the first output node  60   b  or the second output node  60   c  in response to a switching control signal. Accordingly, the first switch  60  provides a signal from the RF signal source to either the first amplifying circuit  70  or the redundancy circuit  80  according to the switching control signal. 
     The first amplifying circuit  70  includes an input impedance matching circuit  72 , an amplifying stage  74 , and an output impedance matching circuit  76 . The input impedance matching circuit  72  matches the impedance of the first amplifying circuit  70  to the impedance of a transmission line connecting the first switch  60  and the first amplifying circuit  70  at the input stage of the first amplifying circuit  70 , so that the reflection of the input signal at the input stage is minimized. The amplifying stage  74  is biased by a biasing circuit  78  and amplifies the signal supplied through the input impedance matching circuit  70 . The output impedance matching circuit  76  matches an impedance of the first amplifying circuit  70  to the impedance of a transmission line connecting the first amplifying circuit  70  and the second switch  90  at the output stage of the first amplifying circuit  70 , so that the reflection of the amplified signal at the output stage is minimized. 
     Two input nodes  90   a  and  90   b  of the second switch  90  are connected to the output terminals of the first amplifying circuit  70  and the redundancy circuit  80 , respectively. The output node  90   c  of the second switch  90  is connected to an external signal processing circuit. The output node  90   c  of the second switch  90  is electrically connected to the first input node  90   a  or the second input node  90   b  in response to the switching control signal. Accordingly, the second switch  90  selects either the output of the first amplifying circuit  70  or that of the redundancy circuit  80  according to the switching control signal, and outputs the selected signal to the signal processing circuit. 
     The control signal generator  92  monitors the operation status of the first amplifying circuit  70  and generates the switching control signal, of which level changes based on the monitored result. In the present embodiment, the control signal generator  92  monitors the normality of the biasing voltage Vb provided by the biasing circuit  78  to the amplifying stage  74  to change the level of the switching control signal. Alternatively, the control signal generator  92  may detect the current or voltage level of the input signal of the first amplifying circuit  70  in addition to the biasing voltage Vb to reflect the current or voltage level in determining the level of the switching control signal. In FIG. 7, the function and operation of a status indicator  94  and a reset circuit are the same as those in FIG. 3, and thus detailed description thereof is omitted. 
     FIG. 8 illustrates yet still another embodiment of the low-noise amplifier according to the present invention. The low-noise amplifier of FIG. 8 has a similar configuration to that of FIG. 7 except the redundancy circuit  80 . In FIG. 8, the redundancy circuit  80  includes an amplifying circuit having at least one amplifying stage  86  biased by a biasing circuit  89 . Accordingly, the redundancy circuit  80  can amplify an input signal rather than simply bypassing the input signal. In case that one of two amplifying circuits is inoperable, the other one can perform the amplification of the input signal. Since the other features of the low-noise amplifier of FIG. 8 is the same as those of the amplifier of FIG. 7, the detailed description thereof is omitted. 
     Although the present invention has been described in detail above, it should be understood that the foregoing description is illustrative and not restrictive. Those of ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics. 
     Accordingly, the scope of the invention should be interpreted in the light of the following appended claims.