This is sentence from Design of Analog CMOS Integrated Circuit that I don't understand.
Note that the current source injects current into ground or draw current from VDD. In other words, only one terminal of each current source is "floating".
Does this mean that, for a MOSFET to be used as a current source, the source of an NMOS should be connected to ground and the source of an PMOS should be connected to VDD?
No other cases are possible?
I mean for example for NMOS, the source may be connected to something else than to ground.
Best Answer
"... No other cases are possible?" Other cases are possible. You can design a floating current source
Note that you really have to have a feedback mechanism that ensures a correct operating point for all the devices. Please consult this paper A low-offset low-voltage CMOS op amp with rail-to-rail input and output ranges and many more by searching "floating current source"