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https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> a question about ft https://designers-guide.org/forum/YaBB.pl?num=1146242099 Message started by frankaurora on Apr 28th, 2006, 9:34am |
Title: a question about ft Post by frankaurora on Apr 28th, 2006, 9:34am to a given process such as 0.18u cmos,if L is a definite value,i think ft is constant,but some book say ft depend on bais condition,am i wrong? thanks for replying :) |
Title: Re: a question about ft Post by milkdragon on Apr 28th, 2006, 12:44pm wt=gm/Cgs where gm is porortional to your sqrt(Id) So you will see ft change with bias |
Title: Re: a question about ft Post by Visjnoe on Apr 29th, 2006, 4:59am Hello, ft ~ tech_const × (Vgs-Vt)/L2 So, ft only depends on the overdrive voltage of your device (bias) and its length. High frequency performance thus requires minimal length and large Vgs-Vt. Kind Regards, Peter |
Title: Re: a question about ft Post by frankaurora on Apr 29th, 2006, 5:38am but refer to Tomas Lee book,it says in short-channel device wt≈const*Esat/L(saturation),so wt is independent of bias? |
Title: Re: a question about ft Post by Visjnoe on May 1st, 2006, 2:14am Hi Frank, the statement in Lee's book is correct, but it describes ft when the transistor is operating in velocity saturation, so the dependency on Vgs-Vt disappears. This effect becomes important for deep-submicron technologies and is less apparent for older technologies (in which the formula I posted previously is valid). Kind Regards Peter |
Title: Re: a question about ft Post by frankaurora on May 6th, 2006, 4:20am :D i got it,thanks a lot! |
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