Re: -Vsb on an n-MOST
Hi dkace
With these conditions you described, there is no difference in usual I-V equations, except that Vth should be changed with its new value (threshold voltage would be less than Vt0, i.e., the threshold voltage when vsb=0).
Vth = Vt0 + γ(sqrt(|2ΦF|+Vsb)-sqrt(|2ΦF|))
where γ is the body-effect coefficient and depends on physical parameters. It is obvious that if Vsb<0 then Vth<Vt0
Actually, that's a common method in low-voltage applications. One can bias the body terminal with a suitable voltage to reduce the Vth to the desired value. However, this reduction of Vth usually leads to more leakage current, which is not desirable in some cases especially in digital applications where there are sometimes millions of transistors on the same chip.
At last but not the least, the body terminal is very precious in low-voltage applications. There are other techniques as well which use this terminal for modulating the Vth, such as CDB (Current Driven Bulk) method.
Regards,
EZT