Attenuator De-Qing Loss Improvement and Phase Balance

Abstract

The de-Qing loss and phase imbalance caused by the inherent capacitance of a switched resistance, such as a MOSFET with a resistor, can be reduced by using a shunting switch across the resistor that is in series with the resistor's switch. The shunting switch shorts across the resistor when the resistor's switch is open and in reference mode, thereby significantly reducing the resistance in series with the inherent capacitance of the open resistor's switch.

1 . (canceled) 
     
     
         2 . An attenuator comprising:
 an attenuator leg comprising:
 a resistive element connected between an input or output of the attenuator and a ground node of the attenuator, the resistive element having a resistance; 
 a primary switching element in series with the resistive element; and 
 a shunting switching element in parallel with the resistive element; 
 wherein the attenuator leg is configured to be operated in two primary states of a) the primary switching element open and the shunting switching element closed, or b) the primary switching element closed and the shunting switching element open; and 
 wherein the attenuator leg is configured such that a phase shift of the attenuator between the two primary states is less than what a second phase shift of the attenuator is between the two states if there is no shunting switching element in the at least one attenuator leg. 
   
     
     
         3 . The attenuator of  claim 2 , wherein the phase shift is at least 2.5 degrees less than the second phase shift over a portion of a frequency range. 
     
     
         4 . The attenuator of  claim 2 , wherein the phase shift is less than half the second phase shift over a portion of a frequency range. 
     
     
         5 . The attenuator of  claim 2 , wherein an insertion loss of the attenuator over the phase shift is at least 0.25 dB less than the insertion loss over the second phase shift. 
     
     
         6 . The attenuator of  claim 2 , wherein the primary switching element and the shunting switching element are MOSFETs, each having a gate width. 
     
     
         7 . The attenuator of  claim 6 , wherein the gate width of the primary switching element is at least four times larger than the gate width of the shunting switching element. 
     
     
         8 . The attenuator of  claim 2 , wherein the attenuator is a pi pad attenuator, a T pad attenuator, an L pad attenuator, or an O pad attenuator.