Ultra-wideband attenuator with low phase variation and improved stability with respect to temperature variations

Abstract

A method for improving the stability and reducing phase variations of an ultra-wideband attenuator, with respect to temperature variations, comprising the steps of providing an attenuator implemented in π-topology and consisting of a serial path between the input and the output of the attenuator, including a first serial resistor Rsconnected to the input, followed by a serial inductor Ls, followed by a second serial resistor Rsconnected to the output; a first transistor Tbridging between the input and the output, for controlling the impedance of the serial path by a first control input provided to the first transistor T; a first parallel path between the input and ground, including a first parallel transistor Tfollowed by first parallel resistor Rp; a second parallel path between the output and ground, including a second parallel transistor Tfollowed by second parallel resistor Rp; a second control input commonly provided to first parallel transistor Tand to the second parallel transistor T, for controlling the impedance of the first and second parallel paths; unifying the serial resistors to a common serial resistor Rs and splitting the serial inductor Ls to two serial inductors Lsand Ls, such that one serial inductor is connected between the input and a first contract of the common serial resistor Rs and the other serial inductor is connected between the output and the other contact of the common serial resistor Rs; splitting the parallel resistor Rpto two smaller resistors, connecting a first smaller resistor to the input, connecting a second smaller resistor to the first smaller resistor via the first parallel transistor Tand to ground via a third parallel transistor T; splitting the parallel resistor Rpto two smaller resistors, connecting a third smaller resistor to the output, connecting a fourth smaller resistor to the third smaller resistor via the second parallel transistor Tand to ground via a fourth parallel transistor T; connecting a first feedback capacitor Cfbbetween the common point connecting between the ungrounded port of the second parallel transistor Tand the first contract of the common serial resistor Rs and connecting a second feedback capacitor Cfbbetween the common point connecting between the ungrounded port of the fourth parallel transistor Tand the second contract of the common serial resistor Rs; upon controlling the first and second parallel transistors Tand Tby the second control input, simultaneously controlling also the third and the fourth parallel transistors Tand Tby the second control input; controlling the first and the second control inputs to obtain a desired attenuation between the input and output of the attenuator.