Discontinuity effect!!!

[abhijitrc]

Hello,

I have a problem that i faced discontinuity problem in my active multiplier((x3) at 17GHz) design: the device i had chosen is PHEMT whose lead width is 0.625mm( gate and drain) but i have to choose 10 mil substrate( alumina 9.8 permitivity), since the line width is 0.25mm and the device lead width is 0.625mm, i hope due to discontinuity i am not able to get a proper conversion loss/gain whatever! plz suggest what i have to do against this!!!!

 

[BigBoss]

I don't think so.. Since your line is discontinued just at the gate/drain, this won't create any problem.
Because small signal and large signal models have been defined at reference point that is component pad land.So, when you design your circuit, you will already reach to this reference point and the circuit
will work.

 

[vfone]

I agree, most of the models are defined at the reference point, but I found that always is room for improving the performance if I design the layout in a manner to minimize the discontinuity effect. Especially when the circuit works at microwave frequencies.

 

[abhijitrc]

Generally we use absorbers in the RF package to avoid any oscillations!, can any body guide me regarding the composition of absorbers and how the absorber works to avoid oscillations!!
2. can oscillations due to DC can be avoided by using absorber.!!

I have seen strong oscillations in my package, due to RF leakage through DC feedback!!
Plz guide me.

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What is the surface current in the package!! can the use of absorber is useful to supress the surface current?