how to simulate fmax

Hello, guys
I wanna see how ft/fmax changes with different Ic to choose best bias for device.
How can I plot this curve in Microwavr Office?

I used the transit time（TFF) to simulate ft：
TFF=TF*{1+XTF*(if/(if+ITF))^2*exp(Vbc/(1.44*VTF))}
and if is the ideal forward diffusion current，if=IS*(exp(Vbe/(NF*Vt))-1)
Then， ft=1/(2PI*TFF)。
However，the simulated ft_VS_Ibias is not a 2nd order curve with a peak，but a monotone decreasing equation。
I don't know why， any help for me?thanks very much

selwyn

Hello,

Follow below steps...
set tau, or Gm as sweep variable in schematic add output equation for ft & then add the IDC measurement to Ic then plot on a graph..

OR

take separate ft/fmax measurement with the equation and a separate measurement for Ic...
Then plot both measurements using Data -> Plot Measurement 1 vs Measurement 2: PlotVs

---manju---

Hi，Manju
thank you very much, but what I really want to know is the exactly ft/fmax equation for simulation. Can you give me some instruction?
Thanks for help.

selwyn