: Hi Joe
: Thank you so much for giving the opinion and sharing the wonderful
: idea.
: That was my initial thought. But I went thinking that there could be
: more before one adopts any convention.
: Nmos if has body effect, meaning the Vsource is higher than Vbulk,
: therefore there could be current flowing to the bulk. Since the arrow
: is pointing to the gate for Nmos, then it might be saying the electron
: is flowing from bulk to source.
: That was a guess with some logic isn't it?
Hey Jason,
Actually, in an NMOS with body effect, there is still not really
any chance of current flowing from source to bulk. I had to draw this out
to re-confirm, but an NMOS has a bulk made out of p-type material, and
source/drain made out of n-type material. The source end of the
source-to-bulk junction (diode) is the CATHODE of the diode, while the
bulk end is the ANODE. If the source (cathode) of that diode is at
a higher voltage than the bulk (anode) the source-to-bulk junction is
reverse biased, and no significant current will from from source-to-bulk
or vice versa.
Forward-biasing either the source-to-bulk or drain-to-bulk
junctions is REALLY BAD, and can lead to latchup. Therefore, that is why
the bulk voltage is picked to be the smallest possible voltage (for the
bulk of NMOS devices, or p-type bulk) and why it is picked to be the
largest possible voltage for the bulk of PMOS devices, which have n-type
bulk.
Hope that helped explain that.....
Joe