a question on the complementary mos switches

[wholx]

during a simulation with spice, i found a weird curve of RonN and RonP versus the input voltage.

let's have a look at the nmos. suppose the VGS=VDD in the simulation. VD=Vin which rises from 0 to 5V linearly.

anyone can tell me what happen if the Vin is reaching VDD-Vthn and then passes it? how about the Ron of the NMOS?

what i see was the Ron surged to several Gohms around VDD-Vthn. well, as the Vin continues to increase, it surged down to several hundred ohms and then began to increase. i dont know what happened. maybe the charge injection changes the Ron during the mode transition period? but the gate control voltage is always VDD, i don't think the charge injection is important here.

any idea is welcome.

thx!

wholx

 

[pseudockb]

Hello, I just did a simulation on the on resistance of MOS switches recently but I did not find anything peculiar. For a NMOS switch, its resistance increases sharply as Vgs approaches Vth and below. Charge injection only occurs only when a switch is open, and I don't see it has anything to do with your obeservation. Maybe you could include your testbench?

 

[vivek_raj_verma]

hi,
at VDD-VTN , for nmos swiched, Ron goes to infinity, its normal. U can see the expression for Ron. For Vin = Vdd-Vtn expression has zero in denominator so Ron is infinity.

Is this what ur quiestion is??????

vicky