The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> what to tweak for getting required VCM?
https://designers-guide.org/forum/YaBB.pl?num=1180609151

Message started by kiran123 on May 31^st, 2007, 3:59am

Title: what to tweak for getting required VCM?
Post by kiran123 on May 31^st, 2007, 3:59am

Hi Experts,

Can any body give me an idea on how to derive a required VCM , i am just desining based on "Andrea Boni" method where in i just used 6 transistors 1NMOS for tail current source and 1 PMOS on top as a current source , middle 4 NMOS as a current switches

now i am able to see a swing(p-p) of 400mV but not on VCM of 1.2 which i wanted it to be ,i.e now the deisgn shwos VOUT = 0.7V and VOUTN = 0.3V but i wanted it to be VOUT= 1.4 and VOUTN=1.0 meaning i wanted to boost VCM from 0.5 to 1.2V but did not understand on which parameter to tweak ?

i have used RA and RB of 100k with 1.2V constant source and terminated OUT and OUTN with 100Ohms and doing the simulations(but i don't understand why should i use 1.2 V using higher resistive network )
without this as well i am not seeing any significant difference exept 1uV in swing

Thanks & Regards
Kiran

Title: what to tweak for getting required VCM? in LVDS
Post by kiran123 on Jun 1^st, 2007, 8:41pm

kiran123 wrote on May 31^st, 2007, 3:59am:

Hi Experts,

Can any body give me an idea on how to derive a required VCM(common mode voltage) , i am just designing based on "Andrea Boni" IEEE paper method where in i just used 6 transistors 1NMOS for tail current source and 1 PMOS on top as a current source , middle 4 NMOS as a current switches

now i am able to see a swing(p-p) of 400mV but not on VCM of 1.2 which i wanted it to be ,i.e now the deisgn it shwos VOUT = 0.7V and VOUTN = 0.3V but i wanted it to be VOUT= 1.4 and VOUTN=1.0 meaning i wanted to boost VCM from 0.5 to 1.2V but did not understand on which parameter to tweak ?

i have used RA and RB of 100k with 1.2V constant source and terminated OUT and OUTN with 100Ohms and doing the simulations(but i don't understand why should i use 1.2 V using higher resistive network )
without this as well i am not seeing any significant difference exept 1uV in swing

Thanks & Regards
Kiran