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I'm trying to remember the approximation for the value of the diffusion capacitance for a bipolar power transistor. I think it might have been gm/Ft? Can anyone confirm this and/or give a reference? Thanks!

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Good old Sedra and Smith fourth edition, pg 322 has the formula as \$C_{de} = \mathrm{T}_{f}*g_m\$ and has a note that \$\mathrm{T}_f\$ is usually in the 10 to 100 picosecond range. It looks like your formula is equivalent.

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Right-click the formula and select "show source" from the MathJax context menu :- \$C_{DE}=\tau_F.g_m\$ – MikeJ-UK Apr 28 '11 at 8:01
@Mike, I didn't know you could do that! Nice... – Adam P Apr 29 '11 at 21:44
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