Stability and enhanced gain of amplifiers using inductive coupling

Abstract

The present invention improves the stability and enhances the gain of amplifiers, particularly transistor amplifiers, by using mutual inductive coupling to partially cancel feedback current. Inductors at the input and output of an amplifier are positioned so that a mutual inductance is created between the two inductors. The mutual inductance is used to cancel the inherent capacitive feedback of transistor amplifiers. The use of mutually coupled inductors allows a large value of effective inductance to be obtained by using relatively small inductors. The use of mutually coupled inductors also avoids the problem of low-frequency instability.

What is claimed is:  
     
         1 . A telephone handset for communicating with a base station, the handset generating and amplifying signals to be transmitted to the base station, the handset comprising: 
 an amplifier for boosting the gain of the signals prior to transmission, the amplifier having capacitive feedback between an input and an output of the transistor wherein a mutual inductance neutralizes the amplifier, the amplifier comprising: 
 a transistor having an input terminal and an output terminal;  
 a first inductor coupled to the input terminal of the transistor; and  
 a second inductor coupled to the output terminal of the transistor, wherein the first inductor and the second inductor are positioned relative to each other to create the mutual inductance between the output terminal of the transistor and the input terminal of the transistor, the mutual inductance resonating with the feedback capacitance in the transistor and wherein the amplifier, the first inductor, and the second inductor are implemented on an integrated circuit without the use of discrete components.  
   
     
     
         2 . The telephone handset of    claim 1   , wherein the telephone handset is a cordless phone.  
     
     
         3 . The telephone handset of    claim 1   , wherein the telephone handset is a cellular phone.  
     
     
         4 . The telephone handset of    claim 1   , wherein the amplifier operates in a frequency range of about 800 MHz and above.  
     
     
         5 . An apparatus comprising: 
 an amplifier having an input terminal and an output terminal;    a first inductor coupled to the input terminal of the amplifier; and    a second inductor coupled to the output terminal of the amplifier, wherein the first inductor and the second inductor are positioned relative to each other to create a mutual inductance which cancels at least a portion of feedback in the amplifier.    
     
     
         6 . The apparatus of    claim 5   , wherein the mutual inductance is between the output terminal of the amplifier and the input terminal of the amplifier.  
     
     
         7 . The apparatus of    claim 6   , wherein the mutual inductance resonates with the feedback capacitance in the amplifier.  
     
     
         8 . The apparatus of    claim 5   , wherein the value of the mutual inductance is small in relation to the value of the first inductor and the second inductor.  
     
     
         9 . The apparatus of    claim 5   , wherein the amplifier is implemented on an integrated circuit.  
     
     
         10 . The apparatus of    claim 9   , wherein the amplifier is a MMIC amplifier.  
     
     
         11 . The apparatus of    claim 5   , wherein the amplifier, the first inductor, and the second inductor are implemented on a semiconductor material without the use of discrete components.  
     
     
         12 . The apparatus of    claim 5   , wherein the amplifier has local minimum feedback at approximately the frequency which provides maximum gain.  
     
     
         13 . The apparatus of    claim 5   , wherein the amplifier operates in a frequency range of about 800 MHz and above.  
     
     
         14 . The apparatus of    claim 5   , wherein the amplifier operates in a frequency range of about 800 MHz to about 2.5 GHz.  
     
     
         15 . The apparatus of    claim 5   , wherein the apparatus amplifies signals for transmission by a telephone handset.  
     
     
         16 . The apparatus of    claim 15   , wherein the telephone handset is part of a remote telephone system.  
     
     
         17 . A method of reducing feedback in an amplifier comprising the acts of: 
 coupling a first inductor to an input terminal of the amplifier;    coupling a second inductor to an output terminal of the amplifier; and    positioning the first inductor and the second inductor relative to each other to create a mutual inductance which cancels at least a portion of the feedback in the amplifier.    
     
     
         18 . The method of reducing feedback of    claim 17   , further comprising the act of estimating the proper placement of the first inductor and the second inductor to achieve the desired mutual inductance.  
     
     
         19 . The method of reducing feedback of    claim 17   , wherein the estimating act is performed by computer simulation.  
     
     
         20 . The method of reducing feedback of    claim 17   , wherein the amplifier, the first inductor, and the second inductor are implemented on a semiconductor material without the use of discrete components.  
     
     
         21 . The method of reducing feedback of    claim 17   , wherein the mutual inductance resonates with a feedback capacitance in the amplifier.  
     
     
         22 . The method of reducing feedback of    claim 17   , wherein the amplifier operates in a frequency range of about 800 MHz and above.  
     
     
         23 . The method of reducing feedback of    claim 17   , wherein the amplifier operates in a frequency range of about 800 MHz to about 2.5 GHz.  
     
     
         24 . The method of reducing feedback of    claim 17   , wherein the amplifier amplifies signals for transmission by a telephone handset.  
     
     
         25 . The method of reducing feedback of    claim 24   , wherein the telephone handset is part of a remote telephone system.  
     
     
         26 . An apparatus comprising: 
 means for amplifying a signal having an input and an output;    first inductive means coupled to the input of the amplifying means; and    second inductive means coupled to the output of the amplifying means, wherein the first inductive means and the second inductive means are positioned relative to each other to create a mutual inductance between the output of the amplifying means and the input of the amplifying means, the mutual inductance neutralizing the amplifying means.    
     
     
         27 . The apparatus of    claim 26   , wherein the value of the mutual inductance is small in relation to the value of the first inductive means and the second inductive means.  
     
     
         28 . The apparatus of    claim 26   , wherein the amplifying means, the first inductive means, and the second inductive means are implemented on a semiconductor material without the use of discrete components.  
     
     
         29 . The apparatus of    claim 26   , wherein the amplifying means has local minimum feedback at approximately the frequency which provides maximum gain.  
     
     
         30 . The apparatus of    claim 26   , wherein the amplifying means operates in a frequency range of about 800 MHz and above.  
     
     
         31 . The apparatus of    claim 26   , wherein the amplifying means operates in a frequency range of about 800 MHz to about 2.5 GHz.  
     
     
         32 . The apparatus of    claim 26   , wherein the amplifying means amplifies the signal for transmission by a telephone handset.  
     
     
         33 . The apparatus of    claim 32   , wherein the telephone handset is part of a remote telephone system.