ft fmax definition

Dear all,

I hear someone said that ft and fmax of the transistor. I just know ft is unity gain cut off frequency. How is about fmax? What is it mean?

Thanks

wccheng

Ft is the unity current gain frequency

Fmax , is the unity power gain frequency also sometimes called max oscillation frequency

khouly

Dear khouly,

Could you tell me how could I simulate fmax? Is the configuration same as ft one? Moreover, is fmax always larger than ft?

Thanks

wccheng

measure the the power gain of the transistor , and sweep it with bias current , coz it is bias dependent , find wen the power gain is unity , this is the fmax


khouly

Cutoff Frequency fT
Frequency, at which the magnitude of the short circuit current gain h21 rolls off to 1 (0 dB).

Maximum Frequency of Oscillation fmax
Frequency, at which the unilateral power gain rolls off to 1 (0 dB).

hi,
as you have said that ft is the unity current gain bandwidth (point where current gain drops to 0 or 1dB).

Now my question is whether it will be the same as unity power bandwidth (frequency at which power gain drops to 0.) I am assuming power is the product voltage and current.

So if current gain is zero, so that should mean that power gain is also zero?
Please give some clarification

thanks
sarfraz

I said that current gain is unitary not zero (zero in dB)

Next if you talk about product of current and voltage you have also to consider where the product is computed (i.e on the load? On the active device? ... ) and the loading conditions

h21 means that the load is a short circuit


Furthermore I stated "unilater power" gain and not power gain... make a search in google for its definition

Ok I made a mistake in giving proper details.
I meant to say unity current gain is where current gain drops to 0 dB or the gain magnitude drops to 1.

But my question still remains, whether the unity current gain point is the same as unity power gain point.

thanks
sarfraz