Ocs package

OCS : Octave Circuit Simulator

Tutorials

A CMOS AND GATE

Schematic for a CMOS AND gate

Here we show how to set up the simulation of the CMOS AND gate in the figure. The circuit has

• 9 Elements
  • 6 MOSFETs (3 n-type + 3 p-type)
  • 3 Voltage sources

For the n-type MOSFETs we use a very simple algebraic model defined by the following code

Code: Model evaluator file for simple MOSFET models

function [a,b,c] = Mnmosfet (string, parameters, parameternames, extvar, intvar, t) switch string case 'simple', rd = 1e6; for ii=1:length(parameternames) eval([parameternames{ii} "=",... num2str(parameters(ii)) " ;"]) endfor vg = extvar(1); vs = extvar(2); vd = extvar(3); vb = extvar(4); vgs = vg-vs; vds = vd-vs; if (vgs < Vth) gm = 0; gd = 1/rd; id = vds*gd; elseif ((vgs-Vth)>=(vds))&(vds>=0) id = k*((vgs-Vth)*vds-(vds^2)/2)+vds/rd; gm = k*vds; gd = k*(vgs-Vth-vds)+1/rd; elseif ((vgs-Vth)>=(vds))&(vds<0) gm = 0; gd = 1/rd; id = vds*gd; else # (i.e. if 0 <= vgs-vth <= vds) id = k*(vgs-Vth)^2/2+vds/rd; gm = k*(vgs-Vth); gd = 1/rd; endif a = zeros(4); b = [ 0 0 0 0; -gm (gm+gd) -gd 0; gm -(gm+gd) gd 0; 0 0 0 0]; c = [0 -id id 0]'; break; otherwise error(["Mnmosfet: unknown option " string]); endswitch endfunction

The model for the p-type devices is entirely analogous.

Below we show three methods for constructing the circuit data structure

• using an Octave script
• parsing a SPICE netlist
• parsing an IFF netlist

Once the circuit data structure is loaded the simulation can be started by the following commands

Code: Run the AND gate simulation

x = [.5 .5 .33 .66 .5 1 0 0 1 ]'; t = linspace (0, .5, 100); pltvars = {"Va", "Vb", "Va_and_b"}; dmp = .2; tol = 1e-15; maxit = 100; out = tst_backward_euler (outstruct, x, t, tol, maxit, pltvars);

Result of the CMOS AND gate switching simulation

Click on the figure to the right to see the simulation results

Build the AND GATE structure directly

Code: Build the AND GATE structure via an Octave script

## NLC # n-type outstruct.NLC(1).func = "Mnmosfet"; outstruct.NLC(1).section = "simple"; outstruct.NLC(1).nextvar = 4; outstruct.NLC(1).npar = 3; outstruct.NLC(1).nparnames = 3; outstruct.NLC(1).parnames = { "k", "Vth", "rd"}; outstruct.NLC(1).pvmatrix = [1.0000e-04 1.0000e-01 1.0000e+07 1.0000e-04 1.0000e-01 1.0000e+07 1.0000e-04 1.0000e-01 1.0000e+07]; outstruct.NLC(1).vnmatrix = [1 3 4 0 2 0 3 0 4 0 5 0]; outstruct.NLC(1).nintvar = [0 0 0]; outstruct.NLC(1).osintvar = [0 0 0]; # p-type outstruct.NLC(2).func = "Mpmosfet"; outstruct.NLC(2).section = "simple"; outstruct.NLC(2).nextvar = 4; outstruct.NLC(2).npar = 3; outstruct.NLC(2).nparnames = 3; outstruct.NLC(2).parnames = { "k", "Vth", "rd"}; outstruct.NLC(2).pvmatrix = [-1.0000e-04 -1.0000e-01 1.0000e+07 -1.0000e-04 -1.0000e-01 1.0000e+07 -1.0000e-04 -1.0000e-01 1.0000e+07]; outstruct.NLC(2).vnmatrix = [ 1 6 4 6 2 6 4 6 4 6 5 6]; outstruct.NLC(2).nintvar = [0 0 0]; outstruct.NLC(2).osintvar = [0 0 0]; # Va and Vb outstruct.NLC(3).func = "Mvoltagesources"; outstruct.NLC(3).section = "sinwave"; outstruct.NLC(3).nextvar = 2; outstruct.NLC(3).npar = 4; outstruct.NLC(3).nparnames = 4; outstruct.NLC(3).parnames = {"Ampl", "f", "delay", "shift"}; outstruct.NLC(3).pvmatrix = [0.50000 1.00000 0.00000 0.50000 0.50000 2.00000 0.25000 0.50000]; outstruct.NLC(3).vnmatrix = [ 1 0 2 0]; outstruct.NLC(3).nintvar = [1 1]; outstruct.NLC(3).osintvar = [0 0]; ## LCR # Vdd outstruct.LCR(1).func = "Mvoltagesources"; outstruct.LCR(1).section = "DC"; outstruct.LCR(1).nextvar = 2; outstruct.LCR(1).npar = 1; outstruct.LCR(1).nparnames = 1; outstruct.LCR(1).parnames = {"V"}; outstruct.LCR(1).pvmatrix = 1; outstruct.LCR(1).vnmatrix = [6 0]; outstruct.LCR(1).nintvar = 1; outstruct.LCR(1).osintvar = 2; ## outstruct.namesn = [1 2 5 6 7 8 9]; outstruct.namess = {"Va", "Vb", "Va_and_b", "Vdd", "I1", "I2", "I3"}; outstruct.totextvar = 6; outstruct.totintvar = 3;

Build the AND gate circuit structure parsing an IFF netlist

To parse an IFF format netlist of the CMOS AND gate we can use the following command

Code: Load the AND circuit structure parsing an IFF netlist

outstruct = prs_iff ("and");

The IFF netlist consists of the .cir file named "and.cir" shown below

Code: IFF netlist for the AND gate (.cir file)

% 0.1b1 % A Simple CMOS AND GATE % % N-Mosfets % There are 3 N-Mosfets Mnmosfet simple 4 3 3 3 k Vth rd 1e-4 0.1 1e7 1e-4 0.1 1e7 1e-4 0.1 1e7 1 3 4 0 2 0 3 0 4 0 5 0 % % P-Mosfets Mpmosfet simple 4 3 3 3 k Vth rd -1e-4 -0.1 1e7 -1e-4 -0.1 1e7 -1e-4 -0.1 1e7 1 6 4 6 2 6 4 6 4 6 5 6 % % Input voltage sources Mvoltagesources sinwave 2 4 2 4 Ampl f delay shift 0.5 1 0.0 0.5 0.5 2 0.25 0.5 1 0 2 0 END % % Power supply Mvoltagesources DC 2 1 1 1 V 1 6 0 END

and of the .nms file named "and.nms shown below

Code: IFF netlist for the AND gate (.nms file)

% 0.1b1 1 Va 2 Vb 5 Va_and_b 6 Vdd 7 I1 8 I2 9 I3

Build the AND gate circuit structure parsing a .spc file

Code: Load the AND circuit structure parsing a .spc file

outstruct = prs_spice ("and");

Code: The .spc file for the CMOS AND gate

* AND (simple Algebraic MOS-FET model) .MODEL mynmos NMOS(LEVEL=simple k=2.94e-05 Vth=0.08 rd=.957e7) .MODEL mypmos PMOS( k=-2.94e-05 Vth=-0.08 rd=.957e7) M1 Va 3 4 0 mynmos M2 Vb 0 3 0 mynmos * nside of the inverter M3 4 0 Va_and_b 0 mynmos M4 Va Vdd 4 Vdd mypmos M5 Vb Vdd 4 Vdd mypmos * pside of the inverter M6 4 Vdd Va_and_b Vdd mypmos V1 Va 0 SIN(0.5 0.5 1 0 0) V2 Vb 0 SIN(0.5 0.5 2 0.25 0) V3 Vdd 0 1 .END