The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Urgent - Strong vs Weak inversion https://designers-guide.org/forum/YaBB.pl?num=1306479750 Message started by pcardoso73 on May 27th, 2011, 12:02am |
Title: Urgent - Strong vs Weak inversion Post by pcardoso73 on May 27th, 2011, 12:02am Hi all, Please try to help me out on this. I am simulating a VCO using 130 nm technology. As BJT's have a lower flicker, I tried the simulation on weak inversion for the MOS, expecting a better behavior than in the strong inversion, in terms of 1/f and 1/f^3. But, by simulations, I cannot reach this conclusion. Any ideas ? Best regards, Pedro |
Title: Re: Urgent - Strong vs Weak inversion Post by solidstate on May 27th, 2011, 10:53am As far as I know, a mosfet does not become a BJT by biasing it in weak inversion, it just shows similar characteristics. The main reason BJTs have low 1/f noise is because they are not surface devices; 1/f noise in mosfets is due to defects at the Si/Si02 interface. The only solution to reduce that noise is by increasing device area.. |
Title: Re: Urgent - Strong vs Weak inversion Post by rfidea on May 27th, 2011, 11:38am solidstate wrote on May 27th, 2011, 10:53am:
I have the same opinon. |
Title: Re: Urgent - Strong vs Weak inversion Post by aaron_do on May 28th, 2011, 8:17am Hi Pedro, the signals in a VCO are large. So I'm not sure that it's fair to say its in the weak inversion or strong inversion region, since more likely it goes from off to weak inversion to strong inversion and finally to triode region, and then back again. There are a few papers on VCO phase noise around, so probably they will have better information. cheers, Aaron |
Title: Re: Urgent - Strong vs Weak inversion Post by pcardoso73 on May 28th, 2011, 10:43am Hi all, Thank you for your replies. Maybe I wasn't very clear. Well I know that both devices are different. Please notice that, in weak inversion, the MOS device operates according an exponential law rather then operating according to a square law. Thus here is some similarity with BJT's. With this assumption, I was expecting that the exponential law behavior would cause a better noise performance. As solidstate said I just need to increase the size of the MOS to get better 1/f noise, but that is to go in the direction of weak inversion. Moreover I will have more problems wih parasitic capacitances of the transistor if the gain of he mosfet is high. Concluding, how is it possible to have a good phase noise behavior on weak inversion ? Tanks to all. Pedro |
Title: Re: Urgent - Strong vs Weak inversion Post by loose-electron on May 28th, 2011, 6:11pm do some research on phase noise in VCO's there are many papers out there. IEEE JSSC is your friend here. |
The Designer's Guide Community Forum » Powered by YaBB 2.2.2! YaBB © 2000-2008. All Rights Reserved. |