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Design >> RF Design >> ft=GBW?
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Message started by rf_man on Aug 7^th, 2008, 12:40am

Title: ft=GBW?
Post by rf_man on Aug 7^th, 2008, 12:40am

Is it completely correct that the GBW of an amplifier is equal to the ft
of the used technology?

Title: Re: ft=GBW?
Post by pancho_hideboo on Aug 7^th, 2008, 12:55am

rf_man wrote on Aug 7^th, 2008, 12:40am:

Is it completely correct that the GBW of an amplifier is equal to the ft
of the used technology?

No, it's completely wrong.

If you mean amplifier which is composed of single transistor and has no parasitic effect regarding bias, etc., GBW will be same as ft.

Title: Re: ft=GBW?
Post by buddypoor on Aug 12^th, 2008, 12:38am

rf_man wrote on Aug 7^th, 2008, 12:40am:

Is it completely correct that the GBW of an amplifier is equal to the ft
of the used technology?

Normally, the term GBW is used only in case of integrated amplifiers (opamps). In this case, GBW is identical to the transit freqency only if the opamp is universal compensated (only one dominant pole in the amplifiying region).
If there is a second pole within this region, the GBW product is larger than Ft.

Title: Re: ft=GBW?
Post by pancho_hideboo on Aug 13^th, 2008, 5:43pm

buddypoor wrote on Aug 12^th, 2008, 12:38am:

In this case, GBW is identical to the transit freqency only if the opamp is universal compensated (only one dominant pole in the amplifiying region).

Starter of this thread mentions "ft of the used technology" not transition frequency of amplifier like following.

rf_man wrote on Aug 7^th, 2008, 12:40am:

Is it completely correct that the GBW of an amplifier is equal to the ft of the used technology?

Title: Re: ft=GBW?
Post by buddypoor on Aug 14^th, 2008, 1:11am

Quote: Starter of this thread mentions "ft of the used technology" not transition frequency of amplifier like following.

Hi, pancho_hideboo

If ft is NOT identical to the transit frequency - what is it ?
Please explain to me. Thank you.

Title: Re: ft=GBW?
Post by pancho_hideboo on Aug 14^th, 2008, 1:19am

buddypoor wrote on Aug 14^th, 2008, 1:11am:

If ft is NOT identical to the transit frequency - what is it ?
Please explain to me.

When we refer to "ft of the used technology", it is a transition frequency of H21 of transistor at some bias condition(e.g. Vds=1.5V, Ids=1mA).
This is NOT identical to the transition frequency of amplifier.

Title: Re: ft=GBW?
Post by buddypoor on Aug 14^th, 2008, 4:13am

pancho_hideboo, thank you.
I was a bit confused as a phrase "ft of technology" is "uncommon" for my opinion..
However, if the transit frequency of the current gain for a transistor was ment, the original question sounds a bit "strange" to me, because it is logical that the GBW of an amplifier (containing some transistors, perhaps of different types) never can equal the transit frequency of one of the transistors.
Thanks and regards