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 - 41 . (canceled)  
   
   
       42 . A trans-conductance amplification circuit comprising: 
 a differential signal input unit; and    a number n (n is a positive integer) of current mirror circuits which select the corresponding mutually different current mirror ratios.    
   
   
       43 . A trans-conductance amplification circuit according to  claim 42 , wherein at least one of current mirror circuits includes multiple switch circuits for outputting mutually different output currents.  
   
   
       44 . A trans-conductance amplification circuit comprising: 
 a signal input unit;    a number n (n is a positive integer) of current mirror circuits including switch circuits for switching and outputting mutually different output currents; and    a switch control circuit which controls the switch circuits.    
   
   
       45 . A trans-conductance amplification circuit comprising: 
 a signal input unit; and    a number n (n is a positive integer) of current mirror circuits;    wherein each of circuits has a switch circuit which is controlled based on a control signal and selectively output multiple mutually different output currents based on the actions of the switch circuits.