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Hole in SMD pad?

Bah, Phil, you should know better. There's no such thing as nH and pF, it's transmission lines all the way down! :)

(The riddle for students being: how can a meter of RG-58 possibly transmit a signal beyond about 100MHz? It has more than 50 ohms worth of inductance* and less than 50 ohms worth of capacitance*, so should be a very effective lowpass filter!)

So if you have 1nH and 1pF, it's probably because you have a transmission line structure of about 63 ohms, with an electrical length resonant at 10GHz (or give or take harmonics).

If you forget that transmission line structures support modes, and generally don't behave like lumped elements, you'll quicky lead yourself to wailing and grinding of teeth, as you realize the transistor goes on and oscillates at whatever damn frequency it pleases. :-)

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com
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Tim Williams
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It's a resonator, but can't really be described as a transmission line, because end effects dominate and its cross-section isn't some nice function of axial position (e.g. a cylinder, taper, etc.).

It'll do that anyway. ;)

Just use the nice bead, keep traces super short and keep I_C under 6 mA, and everything works, even with a high impedance in the source. Of course with the bead it isn't a 40 GHz transistor anymore, but usually I care more about the nice linear beta and especially the practically-infinite V_A.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

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