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Modeling >> Semiconductor Devices >> Fmax and Ft of a device
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Message started by dfury on Apr 21^st, 2011, 3:43am

Title: Fmax and Ft of a device
Post by dfury on Apr 21^st, 2011, 3:43am

Hello all and this is my first post on this forum.

my question is what is Ft and Fmax of a semiconductor device? Can they be calculated from each other? :)

Title: Re: Fmax and Ft of a device
Post by rfidea on Apr 28^th, 2011, 10:18am

Ft is the frequency where the current gain, drain/collector current divided by gate/base current with drain/collector grounded, is one.

Fmax is the frequency where the maximum power gain of the transistor is one.

Ft and Fmax is related but there is no simple relationship. For example the drain/collector capacitance will influence Fmax more than Ft since there is voltage swing there for the Fmax case.

Title: Re: Fmax and Ft of a device
Post by raja.cedt on Nov 12^th, 2011, 10:34am

hello,
in adition to rfidea, Fmax measured under matched load condtion at the drain where as ft measured under short ckt load. you can find simple relation between these in Rf design by TH lee. Mainly that relation depends on the base resistance which impacts Fmax where as no impact on Ft.

Thanks,
raj.