Preamplifier circuit for a photodetector

Abstract

An amplifier circuit ( 20 ) for a photodetector includes a transconductance variable gain stage ( 32 ). The transconductance variable gain stage ( 32 ) has an input ( 34 ) capable of connecting to the photodetector and an output ( 40 ). A transconductance gain stage ( 44 ) has an input ( 42 ) connected to the output ( 40 ) of the transconductance variable gain stage ( 32 ). A feedback resistor ( 46 ) is connected between an output ( 48 ) of the transconductance gain stage ( 44 ) and the input ( 42 ) of the transconductance gain stage ( 44 ).

What is claimed is:  
     
         1 . An amplifier circuit for a photodetector comprising: 
 a transconductance variable gain stage having an input capable of connecting to the photodetector and an output;    a transconductance gain stage having an input connected to the output of the transconductance variable gain stage; and    a feedback resistor connected between an output of the transconductance gain stage and the input of the transconductance gain stage.    
     
     
         2 . The amplifier circuit of  claim 1 , wherein a gain of the transconductance variable gain stage is set to have a predetermined zero gain frequency crossing.  
     
     
         3 . The amplifier circuit of  claim 1 , wherein the transconductance variable gain stage includes a cascoded differential amplifier.  
     
     
         4 . The amplifier circuit of  claim 3 , wherein the transconductance variable gain stage includes a current mirror connected to the cascoded differential amplifier.  
     
     
         5 . The amplifier circuit of  claim 4 , wherein the current mirror includes a positive cascoded current mirror and a negative cascoded current mirror.  
     
     
         6 . The amplifier circuit of  claim 4 , wherein the current mirror has a gain switch.  
     
     
         7 . The amplifier circuit of  claim 6 , wherein the gain switch is controlled by a recording signal.  
     
     
         8 . The amplifier circuit of  claim 1 , wherein the transconductance variable gain stage has a second input connected to a ground.  
     
     
         9 . An amplifier circuit for a photodetector comprising: 
 a transconductance variable gain stage having an input capable of connecting to the photodetector;    a transconductance gain stage having an input connected to an output of the transconductance variable gain stage;    a feedback resistor connected between an output of the transconductance gain stage and the input of the transconductance variable gain stage; and    a variable feedback resistor connected to the input of the transconductance variable gain stage and to the output of the transconductance gain stage.    
     
     
         10 . The amplifier circuit of  claim 9 , wherein the transconductance variable gain stage includes a differential amplifier.  
     
     
         11 . The amplifier circuit of  claim 9 , wherein the differential amplifier is a cascoded differential amplifier.  
     
     
         12 . The amplifier circuit of  claim 10 , wherein the transconductance variable gain stage includes a current mirror connected to the differential amplifier.  
     
     
         13 . The amplifier circuit of  claim 12 , wherein the current mirror includes a gain switch.  
     
     
         14 . The amplifier of  claim 12 , wherein the current mirror includes a positive current mirror and a negative current mirror.  
     
     
         15 . The amplifier of  claim 12 , wherein the current mirror is a cascoded current mirror.  
     
     
         16 . An amplifier circuit for a photodetector comprising: 
 a differential amplifier having an input capable of connecting to the photodetector;    a variable gain positive current mirror connected to the differential amplifier; and    a variable gain negative current mirror connected to the differential amplifier.    
     
     
         17 . The amplifier of  claim 16 , wherein the variable gain positive current mirror includes a positive gain switch.  
     
     
         18 . The amplifier of claim of  16 , further including a transconductance gain stage connected to an output of the variable gain positive current mirror.  
     
     
         19 . The amplifier of  claim 18 , further including a resistor connected between the input of the transconductance gain stage and the output of the transconductance gain stage.