Newbie level 6
I use a buffer opamp to increase the 1.2v bandgap voltage to 4.1v. in the divided resistors, i add a trimming resistors network. when the switch NMOS transistors's bulk are connected to the ground, the temperature dependence of the 4.1v voltage is worse. when these switch NMOS transistors' bulk are connected to their source respectively, the temperature dependence of the 4.1v voltage becomes well. how to explain this phenomenon?