Trans-conductance amplification circuit, trans-conductance filter circuit, and filtering method

Abstract

A trans-conductance filter circuit with an expanded cut-off frequency range is provided. The cut-off frequency of a trans-conductance filter circuit is changed by varying the current mirror ratio of a current mirror circuit. This mirror ratio is varied by changing the output current of a constant current source, or by switching among the respective action states of multiple transistors the actions of which are invoked within constant current regions. The variable cut-off frequency range can be expanded without losing the constant current attributes of the transistors.

1 - 31 . (canceled)  
   
   
       32 . A trans-conductance filter circuit comprising: 
 an amplification circuit which outputs a first output current by triggering a first transistor within a constant current region based on a first control signal and which outputs a second output current by triggering the first transistor and a second transistor within a constant current region based on a second control signal; and    a cut-off frequency generation circuit connected to the amplification circuit and which generates a cut-off frequency for an input signal based on the first output current and the second output current.    
   
   
       33 . The trans-conductance filter circuit according to  claim 32 , including a switch control circuit which controls the generation of the first output current or the second output current.  
   
   
       34 . The trans-conductance filter circuit according to  claim 33 , wherein the switch control circuit includes at least one member selected from among registers, microcomputers, and memories.  
   
   
       35 . The trans-conductance filter circuit according to  claim 32 , including one or two output terminals.  
   
   
       36 . The trans-conductance filter circuit according to  claim 32 , wherein the amplification circuit includes a constant current source or variable current source.  
   
   
       37 . A filtering method comprising: 
 receiving an input signal;    designating a first current mirror ratio or a second current mirror ratio based on a control signal; and    filtering the input signal based on a cut-off frequency proportional to an output current based on the first current mirror ratio or the second current mirror ratio.    
   
   
       38 . A filtering method comprising: 
 receiving an input signal;    outputting a first output current or second output current based on a control signal; and    filtering the input signal based on a cut-off frequency corresponding to the first output current or the second output current.    
   
   
       39 . A filtering method comprising: 
 outputting a first output current by triggering the action of a first transistor within a constant current region based on a first control signal;    outputting a second output current by triggering the respective actions of the first transistor and a second transistor within a constant current region based on a second control signal; and    determining the cut-off frequency in relation to the input signal based on the first output current or the second output current.    
   
   
       40 . A filtering method comprising: 
 outputting a first output current by turning ON a first switch circuit based on a first control signal or outputting a second output current by turning ON said first switch circuit and a second switch circuit based on a second control signal; and    filtering an input signal based on a cut-off frequency corresponding to the first output current or the second output current.    
   
   
       41 . A filtering method comprising: 
 receiving an input signal;    performing a crude adjustment of the output current by selecting a first output current or second output current based on a control signal;    performing a fine adjustment of the output current based on the current of a variable current source; and    filtering the input signal based on a cut-off frequency corresponding to the output current.    
   
   
       42 - 45 . (canceled)