What are exactly ft and fmax of a transistor?

[i_am_here]

What are exactly ft and fmax of transistor and upto what fraction of ft and fmax transistor can be used efficiently?

 

[sengyee88]

ft and fmax

I am not sure about fmax.
But for ft, it represents the theoretical highest speed of a single transistor can give (applicable to small signal only).

However, in real life, there are several limitations that prevent you to achieve that kind of theoretical highest speed:
1. You need gain. Gain and Speed is always a trade off
2. ft actually varied with current. You can plot ft vs current (a curve like a mountain) that tells you what is the optimum bias current for a give transistor size to obtain highest ft.
3. Transistor has parasitic cap. bias current increases -> transistor size increases -> parasitic cap increases -> speed reduces

In general, ft is determined by process. I think to achieve 1/20 of ft speed, should not be a problem over all corners. However, to achieve something less than this, you may need to carefully design the blocks and consider some speed enchancement or bandwidth doubler architectures.

 

[gte582w]

transistor ft

fmax is the maximum freq that you can
get power gain out of the transistor

 

[Verba]

transistor ft fmax

ft: Maximum unity current gain cut-off frequency
fmax: Maximum oscillation frequency

 

[zhangseong]

ft transistor

for a ft doubler, the unity current gain cut-off frequency is doubler.....this not mean the output frequency also double? can this ft doubler circuit be used to multiply frequency?

 

[engrvip]

fmax transistor

ft is called transit freq. fo trans. and theoreticaly speaking it is also Fmax for trans.
and for deisgn purposes we take ft/10 to be the frequecny upto which our trans. will work fine...beyond that there may be no guarantee.

 

[okguy]

fmax ft

Which HSPICE simulation can give me the ft and fmax for a given technology ?

 

[okguy]

transistor fmax

Who has a good paper or doc to describe the HSPICE simulation to run to get FT and FMAX for a given technology ?

 

[A_U_J]

ft vs fmax

Hello all,
can anyone tell intuitively the physical signficance of fT? I mean are we trying to see how fast the channel charge can respond to change in gate current?
finally where does gate leakage come in picture?
thanks so much for the help
thanks,

 

[watersky]

ft of a transistor

I remember there are some introductions in document of foundry. Perhaps you should look for it from these documents.