Abstract:
A radio frequency transceiver includes a mixer circuit configured to convert an intermediate frequency signal into a radio frequency signal, a driver amplifier circuit configured to amplify the radio frequency signal from the mixer circuit, a temperature sensing circuit configured for sensing ambient temperature, and an attenuation circuit connected with the temperature sensing circuit, configured to decreasingly attenuate the radio frequency signal from the driver amplifier circuit as the ambient temperature increases.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a radio frequency transceiver, and relates more particularly to a radio frequency transceiver exhibiting a gain that is unaffected by changes in ambient temperature. 
         [0003]    2. Description of the Related Art 
         [0004]    A satellite transceiver is capable of transmitting and receiving signals by utilizing a satellite communication system. Downlinked satellite signals collected by a parabolic dish are amplified, filtered and converted to signals in a lower frequency range by the satellite transceiver, and signals that are going to be transmitted to satellites are converted to radio frequency signals from intermediate frequency signals, and then filtered and amplified by a power amplifier circuit, and finally coupled to the parabolic dish. 
         [0005]    Usually, the parabolic dish is installed at an outdoor site, and the transceiver is disposed close to the parabolic dish. With changes in weather or changes of seasons, the ambient temperature around the transceiver may fluctuate over a wide range. Such widely fluctuating temperatures may adversely affect the signal transmission of the transceiver. For example, the radio frequency signal gain at the output of the power amplifier circuit may decrease as the ambient temperature around the transceiver increases. Thus, the quality of signals transmitted to a satellite cannot be ensured. 
       SUMMARY OF THE INVENTION 
       [0006]    One aspect of the present invention is to provide a radio frequency transceiver exhibiting a gain that is unaffected by changes in ambient temperature. 
         [0007]    Another aspect of the present invention is to provide a radio frequency transceiver, the gain level of which can be adjusted. 
         [0008]    To fulfill the above aspects, one embodiment of the present invention discloses a radio frequency transceiver, which includes a mixer circuit configured to convert an intermediate frequency signal into a radio frequency signal, a driver amplifier circuit configured to amplify the radio frequency signal from the mixer circuit, a temperature sensing circuit configured for sensing ambient temperature, and an attenuation circuit connected with the temperature sensing circuit, configured to decreasingly attenuate the radio frequency signal from the driver amplifier circuit as the ambient temperature increases. 
         [0009]    Another embodiment of the present invention discloses a radio frequency transceiver, which includes a mixer circuit configured to convert an intermediate frequency signal into a radio frequency signal; a driver amplifier circuit configured to amplify the radio frequency signal from the mixer circuit; an attenuation circuit configured to provide variable attenuation for the level of a radio frequency signal from the driver amplifier circuit; a power amplifier circuit configured to amplify a radio frequency signal from the attenuation circuit, and a temperature sensing circuit configured to provide the attenuation circuit with an attenuation control signal varying with changes in ambient temperature such that the level of a radio frequency signal from the power amplifier circuit is held substantially constant during changes in the ambient temperature. 
         [0010]    To better understand the above-described objectives, characteristics and advantages of the present invention, embodiments, with reference to the drawings, are provided for detailed explanations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will be described according to the appended drawings in which: 
           [0012]      FIG. 1  is a block diagram of a radio frequency transceiver in accordance with one embodiment of the present invention; and 
           [0013]      FIG. 2  shows the reference voltage generating circuit, the temperature sensing circuit, and the voltage scaling circuit according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  is a block diagram of a radio frequency transceiver  1  in accordance with one embodiment of the present invention. Referring to  FIG. 1 , the transceiver  1  comprises a mixer circuit  11 , a band pass filter (BPF) circuit  12 , a driver amplifier circuit  13 , an attenuation circuit  14 , a reference voltage generating circuit  15 , a temperature sensing circuit  16 , a voltage scaling circuit  17 , and a power amplifier circuit  18 . 
         [0015]    A transmitting intermediate frequency (IF) signal is applied to a mixer circuit  11 , mixed with a local oscillation signal LO from a local oscillation circuit (not shown), and frequency-converted to a radio frequency signal provided to the BPF circuit  12 . The BPF circuit  12  filters out unwanted frequencies from the radio frequency signal. The driver amplifier circuit  13  amplifies the filtered radio frequency to output a desired voltage level of the radio frequency signal. The attenuation circuit  14 , the attenuation level of which is controlled by a variable attenuation control signal generated by the temperature sensing circuit  16  configured for sensing the ambient temperature around the radio frequency transceiver  1 , is configured to provide attenuation, decreasing with the increase of the ambient temperature, for the signal level of the amplified radio frequency signal, which also decreases as ambient temperature increases. The attenuation circuit  14  is configured to provide variable attenuation in such a manner that the signal level of the radio frequency signal from the driver amplifier circuit  13  can be held constant during changes in ambient temperature. In one embodiment, using the attenuation circuit  14  controlled by the temperature sensing circuit  16 , the variation of the gain of the radio frequency transceiver  1  can be controlled within a range of 2 dB in response to the variations of ambient temperature. The power amplifier circuit  18  amplifies the attenuated radio frequency signal from the attenuation circuit  14  to a desired output level, and the amplified attenuated radio frequency signal may, for example, be provided to an isolator (not shown) and transmitted by an antenna. 
         [0016]    In one embodiment, the attenuation circuit  14  can be a PIN diode attenuator. 
         [0017]    In addition, in one embodiment of the present invention, the radio frequency transceiver  1  may further comprise a voltage scaling circuit  17 , which connects with the temperature sensing circuit  16  in parallel between the reference voltage generating circuit  15  and the attenuation circuit  14 . The voltage scaling circuit  17 , driven by the reference voltage generating circuit  15 , is employed to provide scaled output voltage so as to change the level of the attenuation control signal applied to the attenuation circuit  14 . The voltage scaling circuit  17  can be configured to cooperate with the power amplifier circuit  18  to set the signal level of the radio frequency signal from the power amplifier circuit  18  to a desired value. 
         [0018]      FIG. 2  shows the reference voltage generating circuit  15 , the temperature sensing circuit  16 , and the voltage scaling circuit  17  according to one embodiment of the present invention. Referring to  FIG. 2 , the reference voltage generating circuit  15  is configured to provide, at point  51 , a reference voltage, which is established by a diode  53  connected in series with a bias resistor R 6  to a voltage source  52 . 
         [0019]    In the present embodiment, the temperature sensing circuit  16  may comprise an amplifier circuit  62  having an output and an inverted input coupled to the output through a resistor R 16 , and a temperature sensor  61  having an input connected with a source of voltage at  63  and an output applying an output voltage V temp , responding to ambient temperature, to the non-inverting input of the amplifier circuit  62  for amplification. The inverting input of the amplifier circuit  62  is also connected, through resistor R 11 , with the output of the reference voltage generating circuit  15  at point  51 . 
         [0020]    In one embodiment of the present invention, the temperature sensing circuit  16  may further include a variable resistor R 9  connected to the output of the amplifier circuit  62  for adjusting the rate of change of the attenuation provided by the attenuation circuit  14  with temperature (dB/degree). 
         [0021]    In one embodiment, the temperature sensor  61  can be a precision integrated circuit temperature sensor. Examples of such precision integrated circuit temperature sensors are those produced by National Semiconductor such as the LM50 or the like. 
         [0022]    Referring to  FIG. 2  again, the voltage scaling circuit  17  may comprise a potentiometer R g , a unit gain amplifier circuit  72 , and an amplifier circuit  73 . The potentiometer R g , configured to provide an adjustable voltage to the unit gain amplifier circuit  72 , is connected between ground and the non-inverting input of the unit gain amplifier circuit  72  with the wiper  71  thereof connected to ground. An inverting input of the amplifier circuit  73  is supplied with a voltage produced by the unit gain amplifier circuit  72 , the non-inverting input of which connects, through resistor R 5 , to the output of the reference voltage generating circuit  15 . The output of the amplifier circuit  73  connects to one end of the resistor R 3 . A feedback resistor R 7  is coupled between the inverting input of the amplifier circuit  73  and another end of the resistor R 3 . The output voltage, V 3 , at point  74  is as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     3 
                   
                   = 
                   
                     
                       - 
                       
                         
                           
                             R 
                             7 
                           
                           × 
                           r 
                         
                         
                           
                             R 
                             2 
                           
                           × 
                           
                             ( 
                             
                               
                                 R 
                                 5 
                               
                               + 
                               
                                 R 
                                 p 
                               
                             
                             ) 
                           
                         
                       
                     
                      
                     
                       V 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where 
         [0023]    V 2  is the voltage at output  51 ; 
         [0024]    R p  is the maximum resistance of resistor R g ; and 
         [0025]    r is a variable resistance value which is between 0 ohm and R g  ohm. 
         [0026]    Referring to  FIG. 2 , the radio frequency transceiver  1  further includes an amplifier circuit  19  having an output for providing an attenuation control signal to the attenuation circuit  14 , a non-inverting input being grounded, and an inverting input coupled with the output of the amplifier circuit  73  through resistors R 3 , R 4  and the output of the amplifier circuit  62  through resistor R 9 . The value of the attenuation control signal, an output voltage V o  in the present embodiment, at an input  41  is as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     o 
                   
                   = 
                   
                     - 
                     
                       ( 
                       
                         
                           
                             
                               R 
                               8 
                             
                             
                               R 
                               9 
                             
                           
                            
                           
                             V 
                             1 
                           
                         
                         + 
                         
                           
                             
                               R 
                               8 
                             
                             
                               R 
                               4 
                             
                           
                            
                           
                             V 
                             3 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where 
         [0027]    V 1  is the voltage at point  64 ; and 
         [0028]    V 3  is determined by Equation (1). 
         [0029]    And, the value of voltage V 1  can be further determined as follows: 
         [0000]    
       
         
           
             
               V 
               1 
             
             = 
             
               
                 
                   V 
                   temp 
                 
                  
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         R 
                         16 
                       
                       
                         R 
                         11 
                       
                     
                   
                   ) 
                 
               
               - 
               
                 
                   V 
                   2 
                 
                  
                 
                   
                     R 
                     16 
                   
                   
                     R 
                     11 
                   
                 
               
             
           
         
       
     
         [0000]    where 
         [0030]    V temp  is the temperature-related signal provided to the non-inverting input of the amplifier circuit  62 . 
         [0031]    As shown in Equations (1) and (2), moving the wiper  71  of the potentiometer R g  can scale the voltage V 3  up or down, consequently changing the signal level of voltage V o , changing the attenuation level of the attenuation circuit  14 , and finally adjusting the signal level of the power amplifier circuit  18 . 
         [0032]    In summary, one embodiment of the present invention provides a radio frequency transceiver, which includes an attenuation circuit controlled by a temperature sensing circuit. The attenuation circuit provides high attenuation for the signal on the main signal path of the radio frequency transceiver when ambient temperature is low and low attenuation for the signal on the main signal path of the radio frequency transceiver when ambient temperature is high. As such, the gain of the radio frequency transceiver can be held constant during ambient temperature changes. 
         [0033]    The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.