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characteristic impedance of Varactor Diode

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Junior Member level 2
Jun 3, 2009
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I wan to design a frequency multiplier with ADS, A GaAs Varactor Diode has been chosen to act as the nonliner device, and I have got the Spice Parameter of the diode. In order to get better efficiency, a good match of input port and output port of Varactor Diode should be done. So, How to simulate the input and output characteristic impedance of the diode in ADS? Is there any tutorial……

THX for your help, best wishes!

P. Penfield and R. P. Rafuse, Varactor Applications. Cambridge: M.I.T. Press, 1962, is the bible.

Basically, the capacitive part of the diode impedance is 2X the junction capacitance at breakdown voltage. The resistive part is determined by how you load all the harmonic currents, but for some simple cases, they give the resistive part (its been a while, but resistances in the 5-20 ohm range come to mind).

Of course, that would just be a starting point. With a modern nonlinear cad program, IF you model the diode properly, you can optimize better today. You need all the diode parameters modelled well, like punch-through, drift velocities, etc etc.

Remember, you need to terminate each of the harmonic frequencies (called idler frequencies) properly to get the optimum efficiency. If you were making a X5 multiplier, there are specific impedances that diode terminals must see at X2, X3, and X4 of the input frequency.

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