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https://designers-guide.org/forum/YaBB.pl Design Languages >> Verilog-AMS >> What is $Vt for a ordinary diode in veriloga code https://designers-guide.org/forum/YaBB.pl?num=1158080527 Message started by gmadhavareddy on Sep 12th, 2006, 10:02am |
Title: What is $Vt for a ordinary diode in veriloga code Post by gmadhavareddy on Sep 12th, 2006, 10:02am Hi, I want to change the model of Schottky diode which is avilable in Cadence ahdlLib. I want to know the $Vt and what $ indicates in veriloga code? Vd = V(vanode, vcathode); `ifdef __VAMS_ENABLE__ Id = I(<vanode>); `else Id = I(vanode, vanode); `endif // intrinsic diode. if (Vd < -5*n*$vt) begin if (Vd == -bv) begin I(vanode, vcathode) <+ -area*ibv; end else if (Vd > -bv) begin I(vanode, vcathode) <+ -area*is; end else begin I(vanode, vcathode) <+ -area*is*(exp(-(bv + Vd)/$vt) - 1 + bv/$vt); end end else begin I(vanode, vcathode) <+ area*is*(exp((Vd - rs*Id)/(n*$vt)) - 1); end I(vanode, vcathode) <+ gmin * Vd; // capacitance (junction and diffusion). if (Vd <= fcp) begin Qd = tt*Id + area*cjo*phi*(1 - pow((1 - Vd/phi), (1 - m)))/(1 - m); end else begin Qd = tt*Id + area*cjo*(f1 + (1/f2)*(f3*(Vd - fcp) + (0.5*m/phi)* (Vd*Vd - fcp*fcp))); end I(vanode, vcathode) <+ ddt(Qd); |
Title: Re: What is $Vt for a ordinary diode in veriloga c Post by Ken Kundert on Sep 12th, 2006, 10:04am $vt is kT/q. |
Title: Re: What is $Vt for a ordinary diode in veriloga c Post by Geoffrey_Coram on Sep 12th, 2006, 12:33pm The $ (dollar sign) is usually used for "system functions and tasks," ie, things the simulator handles: $strobe, $fopen, etc. Also $temperature, which is the simulation temperature. |
Title: Re: What is $Vt for a ordinary diode in veriloga c Post by gmadhavareddy on Sep 28th, 2006, 8:11am Thank you. I have some more doubts to clarify clearly. 1) Is $vt represents threshold voltage or not? 2) If yes, here in this verilog model, they used $vt same for both ordinary diode and schottky diode. /Madhav |
Title: Re: What is $Vt for a ordinary diode in veriloga c Post by ACWWong on Sep 28th, 2006, 8:35am gmadhavareddy wrote on Sep 28th, 2006, 8:11am:
1) As ken said, $vt is kT/q, the thermal voltage. so NO $vt does not reperesent threshold voltage 2) . |
Title: Re: What is $Vt for a ordinary diode in veriloga c Post by jbdavid on Sep 30th, 2006, 1:52am $vt represents Vt a "thermal voltage" as most diodes have a forward Current Id = Is exp(-n⋅Vd/Vt) which of course comes from the carrier density equation (see "Physics of Semiconductor Physics" by S. M. Sze chapter 1) kT/q shows up so often in device equations because of this that the early users decided this needed to be a "built-in" function. because it depends on temperature it cannot be a "constant" Jbd |
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