# Need help with using Findroot

Posted 10 years ago
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 Clear["Global'*"]  Vtn = 1; Vtp = 1; kn = 1; kp = 1; \[Lambda] = 0.02; Vdd = 5; Ids[Vgs_, Vds_] := \[Piecewise] {   {0, Vgs < Vtn},   {kn*((Vgs - Vtn)*Vds - 1/2 Vds^2)*(1 + \[Lambda]*Vds),     Vgs >= Vtn && Vds < Vgs - Vtn},   {1/2*kn*(Vgs - Vtn)^2*((1 + \[Lambda]*Vds)),     Vgs >= Vtn && Vds >= Vgs - Vtn}  }Isd[Vgs_, Vds_] := \[Piecewise] {   {0, Vgs < Vtp},   {kp*((Vdd - Vgs  - Vtp)*(Vdd - Vds) -        1/2 (Vdd - Vds)^2)*(1 + \[Lambda]*(Vdd - Vds)),     Vgs >= Vtp && Vds >= Vgs - Vtp},   {1/2*kp*(Vdd - Vgs - Vtp)^2*((1 + \[Lambda]*(Vdd - Vds))),     Vgs >= Vtp && Vds <=  Vgs - Vtp}  }Table[FindRoot[  1/2*kn*(Vgs - Vtn)^2*((1 + \[Lambda]*Vds)) ==    kp*((Vdd - Vgs - Vtp)*(Vdd - Vds) -       1/2 (Vdd - Vds)^2)*(1 + \[Lambda]*(Vdd - Vds)), {Vgs, 0}], {Vgs,   0, 5}]Hi, I am very new to using Mathematica however my professor believes we all know how to use it. Any help and tips would be great.I am trying to use the FindRoot function to find Vds for Vgs input of 0 to 5 then table it so that I can Plot the graph of Vds Vs. Vgs which is the VTC curve of the inverter. But I can not seem to get find root to work.Once again thanks for any help, you can give me.