Attenuator

Abstract

In the existing technique in which the attenuation characteristic of an attenuator is adjusted by a voltage value, there are problems that a scale of a circuit of the attenuator increases because a new circuit for supplying voltage such as a step-down circuit becomes necessary, and that a thermal noise and a shot noise are mixed in an output signal of the attenuator. To solve the above-mentioned problems, provided is an attenuator comprising a T-type two terminal pair network including first and second circuits connected in series, and a third circuit connected in shunt between these first and second circuits. A shunt capacitor is connected between the first and second circuits independent from the third circuit.

1 . An attenuator comprising:
 a T-type two terminal pair network including first and second terminals, first, second and third circuits, wherein said first terminal receives an input signal to be attenuated, wherein said first circuit is connected between said first and second terminals, wherein said second circuit is connected between said first circuit and said second terminal and is connected to said first circuit via a node, wherein said third circuit is connected to said node; and   a capacitor connected to said node, wherein an amount of attenuation of said input signal is adjusted by a capacitance value of said capacitor.   
     
     
         2 . The attenuator according to  claim 1 , wherein said capacitor is connected in parallel with said third circuit. 
     
     
         3 . The attenuator according to  claim 1 , wherein said capacitance value of said capacitor is variable. 
     
     
         4 . The attenuator according to  claim 1 , further comprising:
 another capacitor connected between said first terminal and said first circuit.   
     
     
         5 . The attenuator according to  claim 1 , wherein said first circuit includes a field effect transistor having a gate terminal connected to a resistor. 
     
     
         6 . The attenuator according to  claim 1 , further comprising:
 a field effect transistor connected between said node and said capacitor.   
     
     
         7 . The attenuator according to  claim 1 , further comprising:
 another capacitor connected to said node, wherein an amount of attenuation of said input signal is adjusted by capacitance values of said capacitor and said another capacitor.   
     
     
         8 . The attenuator according to  claim 7 , wherein each of said capacitor and said another capacitor is connected in parallel with said third circuit.