Variable gain amplifier for use in communications

Abstract

A variable gain amplifier of low amplitude distortion, and low noise, having a large variable range, is provided. A variable gain differential amplifier that controls a gain by use of bias current is used as each of unit amplifiers (VGAs) making up the variable gain amplifier. A large variable gain range is obtained by series-connecting a plurality of the variable gain differential amplifiers. An attenuator is installed on the input side of the unit amplifier (VGA) at least in the initial stage. By doing so, it becomes possible to prevent amplitude distortion from occurring to the respective VGAs. An attenuator utilizing voltage division by capacitors, generating no noise, is used for lowering noise. Further, the variable gain amplifier is provided with a fixed gain amplifier installed in the final stage as necessary in order to obtain a total gain as desired. With the use of the variable gain amplifier as a variable gain amplifier for output power control of a polar loop transmitter, an excellent function for output power control can be achieved without causing significant deterioration in distortion characteristic and noise characteristic thereof.

1 - 16 . (canceled)  
   
   
       17 . A polar loop transmitter comprising: 
 a modulator configured to output a modulated signal; an amplitude loop having an amplitude comparator;    a phase loop having a phase comparator; and    a down-convert mixer configured to convert a frequency of a feedback signal detecting an output of a power amplifier into an intermediate frequency band and thereby further configured to output an intermediate frequency signal, wherein the amplitude comparator is configured to compare an amplitude component of the modulated signal with an amplitude component of the intermediate frequency signal such that the amplitude loop is configured to provide amplitude feedback to a control terminal, wherein the phase comparator is configured to compare a phase component of the modulated signal with a phase component of the intermediate frequency signal such that the phase loop is configured to provide phase comparisons to a transmission voltage control oscillator, wherein the transmission voltage control oscillator is thereby configured to input a transmission signal that is phase-modulated to the power amplifier, wherein the polar loop transmitter is configured to transmit the transmission signal after amplification by the power amplifier; and    a variable gain amplifier connected between the down-convert mixer, the amplitude comparator, and the phase comparator, wherein the variable gain amplifier is configured to facilitate output power control of the power amplifier.    
   
   
       18 . The polar loop transmitter of  claim 17 , wherein the variable gain amplifier has a multiple-stage configuration, the variable gain amplifier comprising: 
 a plurality of variable gain unit amplifiers connected in series, wherein the plurality of variable gain unit amplifiers are configured to obtain a large variable gain range for the variable gain amplifier, wherein each of the plurality variable gain unit amplifiers has a differential input side; and    a plurality of low nose attenuators, wherein each of the plurality of low noise attenuators is connected to the differential input side of each of the plurality of variable gain unit amplifiers.    
   
   
       19 . The polar loop transmitter of  claim 18 , wherein the variable gain amplifier further comprises a final stage having a fixed gain amplifier.  
   
   
       20 . The polar loop transmitter of  claim 18 , wherein at least one of the plurality of variable gain unit amplifiers includes a variable gain differential amplifier.  
   
   
       21 - 28 . (canceled)  
   
   
       29 . A transmitter comprising: 
 a modulator configured to output a modulated signal;    an amplitude loop having an amplitude comparator;    a phase loop having a phase comparator;    a down-convert mixer configured to convert a frequency of a feedback signal detecting an output of a power amplifier into an intermediate frequency band and configured to output an intermediate frequency signal, wherein the amplitude comparator is configured to compare an amplitude component of the modulated signal with an amplitude component of the intermediate frequency signal such that the amplitude loop is configured to provide amplitude feedback to a control terminal, wherein the phase comparator is configured to compare a phase component of the modulated signal with a phase component of the intermediate frequency signal such that the phase loop is configured to provide phase comparisons to a transmission voltage control oscillator, wherein the transmission voltage control oscillator is thereby configured to input a transmission signal that is phase-modulated to the power amplifier, and wherein the transmitter is configured to transmit the transmission signal after amplification by the power amplifier; and    a variable gain amplifier connected between the down-convert mixer, the amplitude comparator, and the phase comparator,    wherein the variable gain amplifier has a multiple-stage configuration, and comprises:    a plurality of variable gain unit amplifiers connected in series, wherein the plurality of variable gain unit amplifiers are configured to obtain a large variable gain range for the variable gain amplifier, wherein each of the plurality variable gain unit amplifiers has a differential input side; and    a plurality of low noise attenuators, wherein each of the plurality of low noise attenuators is connected to the differential input side of each of the plurality of variable gain unit amplifiers.    
   
   
       30 . The transmitter of  claim 29 , 
 wherein at least one of the plurality of noise attenuators is configured to perform voltage division via capacitors, wherein the at least one of the plurality of low noise attenuators comprises:    a first capacitor;    a second capacitor; and    a third capacitor, wherein differential input terminals are connected to a first terminal of the first capacitor and to a first terminal of the second capacitor, wherein a third capacitor is connected between a second terminal of the first capacitor and a second terminal of the second capacitor, wherein differential output terminals are connected to the second terminal of the first capacitor and to the second terminal of the second capacitor.    
   
   
       31 . The transmitter of  claim 29 , further comprising a final stage having a fixed gain amplifier.  
   
   
       32 . The transmitter of  claim 30 , further comprising a final stage having a fixed gain amplifier.  
   
   
       33 . The transmitter of  claim 29 , 
 wherein at least one of the plurality of variable gain unit amplifiers includes a variable gain differential amplifier.    
   
   
       34 . The transmitter of  claim 30 , 
 wherein at least one of the plurality of variable gain unit amplifiers includes a variable gain differential amplifier.    
   
   
       35 . The transmitter of  claim 31 , 
 wherein at least one of the plurality of variable gain unit amplifiers includes a variable gain differential amplifier.    
   
   
       36 . The transmitter of  claim 32 , 
 wherein at least one of the plurality of variable gain unit amplifiers includes a variable gain differential amplifier.    
   
   
       37 . The transmitter of  claim 33 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source, wherein an emitter of the first transistor is bonded to an emitter of the second transistor to form bonded emitters; a variable current source connected between the bonded emitters and a ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       38 . The transmitter of  claim 34 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source, wherein an emitter of the first transistor is bonded to an emitter of the second transistor to form bonded emitters; a variable current source connected between the bonded emitters and a ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       39 . The transmitter of  claim 35 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source, wherein an emitter of the first transistor is bonded to an emitter of the second transistor to form bonded emitters; a variable current source connected between the bonded emitters and a ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       40 . The transmitter of  claim 36 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source, wherein an emitter of the first transistor is bonded to an emitter of the second transistor to form bonded emitters;    a variable current source connected between the bonded emitters and a ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       41 . The transmitter of  claim 33 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source;    a first diode connected between an emitter of the first transistor and a ground;    a second diode connected between an emitter of the second transistor and the ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       42 . The transmitter of  claim 34 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source;    a first diode connected between an emitter of the first transistor and a ground;    a second diode connected between an emitter of the second transistor and the ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       43 . The transmitter of  claim 35 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source;    a first diode connected between an emitter of the first transistor and a ground;    a second diode connected between an emitter of the second transistor and the ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.    
   
   
       44 . The transmitter of  claim 36 , wherein the variable gain differential amplifier comprises: 
 a first transistor;    a second transistor;    a first load resistor connected between a collector of the first transistor and a power source;    a second load resistor connected between a collector of the second transistor and the power source;    a first diode connected between an emitter of the first transistor and a ground;    a second diode connected between an emitter of the second transistor and the ground;    differential input terminals connected to a base of the first transistor and to a base of the second transistor; and    differential output terminals connected to the collector of the first transistor and to the collector of the second transistor.