Variable gain amplifying apparatus and wireless communication apparatus

Abstract

A variable gain amplifying apparatus has an amplifier; one or more first switching elements connected in parallel to the amplifier; and a phase shifter connected in series to the first switching element, wherein the first switching element is enabled if the level of an input signal or an output signal is higher than a predetermined level, and the first switching element is disabled if the level of the input signal or the output signal is equal to or lower than the predetermined level, the amplifier does not operate when the first switching element is enabled, and the amplifier operates when the first switching element is disabled, and the amount of phase shift when the input signal is passed through the amplifier and phase shifter is substantially equal to the amount of phase shift when the input signal is passed through the first switching element.

What is claimed is:  
     
         1 . A variable gain amplifying apparatus comprising: 
 an amplifier;    one or more first switching elements connected in parallel to said amplifier; and    a phase shifter connected in series to said first switching element,    wherein said first switching element is enabled if the level of an input signal or an output signal is higher than a predetermined level, and said first switching element is disabled if the level of said input signal or said output signal is equal to or lower than said predetermined level,    said amplifier does not operate when said first switching element is enabled, and said amplifier operates when said first switching element is disabled, and    the amount of phase shift when said input signal is passed through said amplifier and phase shifter is substantially equal to the amount of phase shift when said input signal is passed through said first switching element.    
     
     
         2 . A variable gain amplifying apparatus comprising: 
 an amplifier;    one or more first switching elements connected in parallel to said amplifier;    a phase shifter connected in series to said first switching element;    one or more second switching elements connected in parallel to said amplifier; and    a feedback circuit connected in series to said second switching element,    wherein said first switching element is enabled if the level of an input signal or an output signal is higher than a predetermined level, and said first switching element is disable if the level of said input signal or said output signal is equal to or lower than said predetermined level,    said amplifier does not operate when said first switching element is enabled, and said amplifier operates when said first switching element is disabled,    said second switching element is disabled when said first switching element is enabled,    said second switching element is enabled when said first switching element is disabled, and    the amount of phase shift when said input signal is passed through said amplifier is substantially equal to the amount of phase shift when said input signal is passed through said first switching element and said phase shifter.    
     
     
         3 . The variable gain amplifying apparatus according to  claim 1 , wherein said first switching element is comprised of one or more third switching elements and one or more fourth switching elements, 
 one end of said third switching element is connected to the input of said amplifier,    the other end of said third switching element is connected to one end of said phase shifter,    the other end of said phase shifter is connected to one end of said fourth switching element, and    the other end of said fourth switching element is connected to the output of said amplifier.    
     
     
         4 . The variable gain amplifying apparatus according to  claim 2 , wherein said first switching element is comprised of one or more third switching elements and one or more fourth switching elements, 
 one end of said third switching element is connected to the input of said amplifier,    the other end of said third switching element is connected to one end of said phase shifter,    the other end of said phase shifter is connected to one end of said fourth switching element, and    the other end of said fourth switching element is connected to the output of said amplifier.    
     
     
         5 . A variable gain amplifying apparatus comprising: 
 an amplifier;    one or more switching elements connected in parallel to said amplifier; and    a phase shifter connected in series to said amplifier,    wherein said switching element is enabled if the level of an input signal or an output signal is higher than a predetermined level, and said switching element is disable if the level of said input signal or said output signal is equal to or lower than said predetermined level,    said amplifier does not operate when said switching element is enabled, and said amplifier operates when said switching element is disabled, and    the amount of phase shift when said input signal is passed through said amplifier and phase shifter is substantially equal to the amount of phase shift when said input signal is passed through said first switching element.    
     
     
         6 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more serial-connected capacitors and one or more parallel-connected resistors.  
     
     
         7 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more serial-connected resistors and one or more parallel-connected capacitors.  
     
     
         8 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more strip lines, and said strip lines are connected so that a characteristic impedance monotonously increases or monotonously decreases.  
     
     
         9 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more parallel twin lines, and said parallel twin lines are connected so that a characteristic impedance monotonously increases or monotonously decreases.  
     
     
         10 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more serial-connected capacitors and one or more parallel-connected inductors.  
     
     
         11 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein said phase shifter is comprised of one or more serial-connected inductors and one or more parallel-connected capacitors.  
     
     
         12 . The variable gain amplifying apparatus according to any of  claims 1  to  5 , wherein one end or both ends of said switching element are connected to the ground through the resistor or the inductor.  
     
     
         13 . A wireless communication apparatus comprising the variable gain amplifying apparatus according to any of  claims 1  to  5 , and using phase modulation signals as send/receive signals.  
     
     
         14 . A wireless communication apparatus comprising: 
 the variable gain amplifying apparatus according to any of  claims 1  to  5 ;    a level detection circuit detecting the level of a receive signal in the rear of said variable gain amplifying apparatus; and    a control circuit switching the gain of said variable gain amplifying apparatus,    wherein said variable gain amplifying apparatus is switched to a low gain state if the level detected by said level detection circuit is higher than a predetermined level; and    said variable gain amplifying apparatus is switched to a high gain state if the level detected by said level detection circuit is equal to or lower than said predetermined level.    
     
     
         15 . A wireless communication apparatus comprising: 
 the variable gain amplifying apparatus according to any of  claims 1  to  5 ;    a channel selection filter;    a first level detection circuit detecting the level of a receive signal in the front stage of the channel selection filter;    a second level detection circuit detecting the level of a receive signal in the rear stage of the channel selection filter; and    a control circuit switching the gain of said variable gain amplifying apparatus,    wherein the output of said variable gain amplifying apparatus is inputted to said channel selection filter,    said variable gain amplifying apparatus is switched to a low gain state if the level detected by said second level detection circuit is higher than a first predetermined level,    said variable gain amplifying apparatus is switched to a high gain and low current state if the level detected by said second level detection circuit is equal to or lower than said first predetermined level, and the level detected by said first level detection circuit is equal to or lower than a second predetermined level, and    said variable gain amplifying apparatus is switched to a high gain and high current state if the level detected by said second level detection circuit is equal to or lower than said first predetermined level, and the level detected by said first level detection circuit is equal to or lower than said second predetermined level.