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edx-platform/js/cktsim.js
Piotr Mitros 7600920f76 CJT's new schematic editor
2012-01-16 13:29:57 -05:00

1338 lines
41 KiB
JavaScript
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//////////////////////////////////////////////////////////////////////////////
//
// Circuit simulator
//
//////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2011 Massachusetts Institute of Technology
// create a circuit for simulation using "new cktsim.Circuit()"
// for modified nodal analysis (MNA) stamps see
// http://www.analog-electronics.eu/analog-electronics/modified-nodal-analysis/modified-nodal-analysis.xhtml
cktsim = (function() {
///////////////////////////////////////////////////////////////////////////////
//
// Circuit
//
//////////////////////////////////////////////////////////////////////////////
// types of "nodes" in the linear system
T_VOLTAGE = 0;
T_CURRENT = 1;
v_newt_lim = 0.3; // Voltage limited Newton great for Mos/diodes
v_abstol = 1e-6; // criterion for absolute convergence (voltage)
i_abstol = 1e-12; // criterion for absolute convergence (current)
min_time_step = 1e-18; // smallest possible time step
max_dc_iters = 200; // max iterations before giving pu
max_tran_iters = 10; // max iterations before giving up
increase_limit = 4; // if we converge in this many iterations, increase time step
time_step_increase_factor = 2.0;
time_step_decrease_factor = 0.3;
reltol = 0.001; // convergence criterion relative to max observed value
function Circuit() {
this.node_map = new Array();
this.ntypes = [];
this.initial_conditions = []; // ic's for each element
this.devices = []; // list of devices
this.device_map = new Array(); // map name -> device
this.finalized = false;
this.diddc = false;
this.node_index = -1;
}
// index of ground node
Circuit.prototype.gnd_node = function() {
return -1;
}
// allocate a new node index
Circuit.prototype.node = function(name,ntype,ic) {
this.node_index += 1;
if (name) this.node_map[name] = this.node_index;
this.ntypes.push(ntype);
this.initial_conditions.push(ic);
return this.node_index;
}
// call to finalize the circuit in preparation for simulation
Circuit.prototype.finalize = function() {
if (!this.finalized) {
this.finalized = true;
this.N = this.node_index + 1; // number of nodes
// give each device a chance to finalize itself
for (var i = this.devices.length - 1; i >= 0; --i)
this.devices[i].finalize(this);
// set up augmented matrix and various temp vectors
this.matrix = this.make_mat(this.N, this.N+1);
this.Gl = this.make_mat(this.N, this.N); // Matrix for linear conductances
this.G = this.make_mat(this.N, this.N); // Complete conductance matrix
this.C = this.make_mat(this.N, this.N); // Matrix for linear L's and C's
this.soln_max = new Array(this.N); // max abs value seen for each unknown
this.abstol = new Array(this.N);
this.solution = new Array(this.N);
this.rhs = new Array(this.N);
for (var i = this.N - 1; i >= 0; --i) {
this.soln_max[i] = 0.0;
this.abstol[i] = this.ntypes[i] == T_VOLTAGE ? v_abstol : i_abstol;
this.solution[i] = 0.0;
this.rhs[i] = 0.0;
}
}
}
// load circuit from JSON netlist (see schematic.js)
Circuit.prototype.load_netlist = function(netlist) {
// set up mapping for ground node always called '0' in JSON netlist
this.node_map['0'] = this.gnd_node();
// process each component in the JSON netlist (see schematic.js for format)
for (var i = netlist.length - 1; i >= 0; --i) {
var component = netlist[i];
var type = component[0];
// ignore wires, ground connections, scope probes and view info
if (type == 'view' || type == 'w' || type == 'g' || type == 's' || type == 'L') continue;
var properties = component[2];
var name = properties['name'];
// convert node names to circuit indicies
var connections = component[3];
for (var j = connections.length - 1; j >= 0; --j) {
var node = connections[j];
var index = this.node_map[node];
if (index == undefined) index = this.node(node,T_VOLTAGE);
connections[j] = index;
}
// process the component
if (type == 'r') // resistor
this.r(connections[0],connections[1],properties['r'],name);
else if (type == 'd') // diode
this.d(connections[0],connections[1],properties['area'],name);
else if (type == 'c') // capacitor
this.c(connections[0],connections[1],properties['c'],name);
else if (type == 'l') // inductor
this.l(connections[0],connections[1],properties['l'],name);
else if (type == 'v') // voltage source
this.v(connections[0],connections[1],properties['value'],name);
else if (type == 'i') // current source
this.i(connections[0],connections[1],properties['value'],name);
else if (type == 'o') // op amp
this.opamp(connections[0],connections[1],connections[2],properties['A'],name);
else if (type == 'n') // n fet
this.n(connections[0],connections[1],connections[2],
properties['W/L'],name);
else if (type == 'p') // p fet
this.p(connections[0],connections[1],connections[2],
properties['W/L'],name);
}
}
// if converges: updates this.solution, this.soln_max, returns iter count
// otherwise: return undefined and set this.problem_node
// The argument should be a function that sets up the linear system.
Circuit.prototype.find_solution = function(load,maxiters) {
var soln = this.solution;
var rhs = this.rhs;
var d_sol,temp,converged;
// iteratively solve until values convere or iteration limit exceeded
for (var iter = 0; iter < maxiters; iter++) {
// set up equations
// no longer needed this.initialize_linear_system();
load(this,soln,rhs);
// Compute the Newton delta
d_sol = solve_linear_system(this.matrix,rhs);
// Update solution and check convergence.
converged = true;
for (var i = this.N - 1; i >= 0; --i) {
// Simple voltage step limiting to encourage Newton convergence
if (this.ntypes[i] == T_VOLTAGE) {
d_sol[i] = (d_sol[i] > v_newt_lim) ? v_newt_lim : d_sol[i];
d_sol[i] = (d_sol[i] < -v_newt_lim) ? -v_newt_lim : d_sol[i];
}
soln[i] += d_sol[i];
if (Math.abs(soln[i]) > this.soln_max[i])
this.soln_max[i] = Math.abs(soln[i]);
thresh = this.abstol[i] + reltol*this.soln_max[i];
if (Math.abs(d_sol[i]) > thresh) {
converged = false;
this.problem_node = i;
}
}
// alert(numeric.prettyPrint(this.solution));
if (converged == true) return iter+1;
}
// too many iterations
return undefined;
}
// DC analysis
Circuit.prototype.dc = function() {
this.finalize();
// Load up the linear part.
for (var i = this.devices.length - 1; i >= 0; --i) {
this.devices[i].load_linear(this)
}
// Define f and df/dx for Newton solver
function load_dc(ckt,soln,rhs) {
// rhs is initialized to -Gl * soln
ckt.matv_mult(ckt.Gl, soln, rhs, -1.0);
// G matrix is initialized with linear Gl
ckt.copy_mat(ckt.Gl,ckt.G);
// Now load up the nonlinear parts of rhs and G
for (var i = ckt.devices.length - 1; i >= 0; --i)
ckt.devices[i].load_dc(ckt,soln,rhs);
// G matrix is initialized with linear Gl
ckt.copy_mat(ckt.G,ckt.matrix);
}
// find the operating point
var iterations = this.find_solution(load_dc,max_dc_iters);
if (typeof iterations == 'undefined') {
return 'Node '+this.node_map[this.problem_node]+' unconverged';
} else {
// Note that a dc solution was computed
this.diddc = true;
// create solution dictionary
var result = new Array();
for (var name in this.node_map) {
var index = this.node_map[name];
result[name] = (index == -1) ? 0 : this.solution[index];
}
return result;
}
}
// Transient analysis (needs work!)
Circuit.prototype.tran = function(ntpts, tstart, tstop, no_dc) {
// Standard to do a dc analysis before transient
// Otherwise, do the setup also done in dc.
if ((this.diddc == false) && (no_dc == false)) this.dc();
else {
// Allocate matrices and vectors.
this.finalize();
// Load up the linear elements once and for all
for (var i = this.devices.length - 1; i >= 0; --i)
this.devices[i].load_linear(this)
}
// Tired of typing this, and using "with" generates hate mail.
var N = this.N;
// build array to hold list of results for each variable
// last entry is for timepoints.
var response = new Array(N + 1);
for (var i = N; i >= 0; --i) response[i] = new Array();
// Allocate space to put previous charge and current
this.oldc = new Array(this.N);
this.oldq = new Array(this.N);
this.c = new Array(this.N);
this.q = new Array(this.N);
this.alpha0 = 1.0;
// Define f and df/dx for Newton solver
function load_tran(ckt,soln,rhs) {
// rhs is initialized to -Gl * soln
ckt.matv_mult(ckt.Gl, soln, ckt.c,-1.0);
// G matrix is initialized with linear Gl
ckt.copy_mat(ckt.Gl,ckt.G);
// Now load up the nonlinear parts of rhs and G
for (var i = ckt.devices.length - 1; i >= 0; --i)
ckt.devices[i].load_tran(ckt,soln,ckt.c,ckt.time);
// Exploit the fact that storage elements are linear
ckt.matv_mult(ckt.C, soln, ckt.q, 1.0);
for (var i = ckt.N-1; i >= 0; --i)
rhs[i] = ckt.alpha0 *(ckt.oldq[i] - ckt.q[i]) + ckt.c[i]
// rhs is initialized to -Gl * soln
ckt.matv_mult(ckt.Gl, soln, ckt.c,-1.0);
// system matrix is G - alpha0 C.
ckt.mat_scale_add(ckt.G,ckt.C,ckt.alpha0,ckt.matrix);
}
this.time = tstart;
var dt = (tstop - tstart)/ntpts;
// Initialize this.c and this.q
load_tran(this,this.solution,this.rhs)
for(var tindex = 0; tindex < ntpts; tindex++) {
// Save the just computed solution, and move back q and c.
for (var i = this.N - 1; i >= 0; --i) {
response[i].push(this.solution[i]);
this.oldc[i] = this.c[i];
this.oldq[i] = this.q[i];
}
response[this.N].push(this.time);
this.oldtime = this.time;
if (this.time >= tstop) break;
// Pick a timestep and an integration method
if (this.time + 1.1*dt > tstop)
this.time = tstop;
else
this.time += dt;
// Set the timestep
this.alpha0 = 1.0/(this.time - this.oldtime);
// Predict the solution, nah maybe later.
// Use Newton to compute the solution.
var iterations = this.find_solution(load_tran,max_tran_iters);
if (iterations == undefined)
alert('timestep nonconvergence, try more time points');
}
// create solution dictionary
var result = new Array();
for (var name in this.node_map) {
var index = this.node_map[name];
result[name] = (index == -1) ? 0 : response[index];
}
result['time'] = response[this.N];
return result;
}
// AC analysis: npts/decade for freqs in range [fstart,fstop]
// result['frequencies'] = vector of log10(sample freqs)
// result['xxx'] = vector of dB(response for node xxx)
// NOTE: Normalization removed in schematic.js, jkw.
Circuit.prototype.ac = function(npts,fstart,fstop,source_name) {
if (this.diddc == false) this.dc();
var N = this.N;
var G = this.G;
var C = this.C;
// Complex numbers, we're going to need a bigger boat
var matrixac = this.make_mat(2*N, (2*N)+1);
// Get the source used for ac
if (this.device_map[source_name] === undefined) {
alert('AC analysis refers to unknown source ' + source_name);
return 'AC analysis failed, unknown source';
}
this.device_map[source_name].load_ac(this,this.rhs);
// build array to hold list of results for each node
// last entry is for frequency values
var response = new Array(N + 1);
for (var i = N; i >= 0; --i) response[i] = new Array();
// multiplicative frequency increase between freq points
var delta_f = Math.exp(Math.LN10/npts);
var f = fstart;
fstop *= 1.0001; // capture that last time point!
while (f <= fstop) {
var omega = 2 * Math.PI * f;
response[this.N].push(f);
// Find complex x+jy that sats Gx-omega*Cy=rhs; omega*Cx+Gy=0
// Note: solac[0:N-1]=x, solac[N:2N-1]=y
for (var i = N-1; i >= 0; --i)
{
// First the rhs, replicated for real and imaginary
matrixac[i][2*N] = this.rhs[i];
matrixac[i+N][2*N] = 0;
for (var j = N-1; j >= 0; --j)
{
matrixac[i][j] = G[i][j];
matrixac[i+N][j+N] = G[i][j];
matrixac[i][j+N] = -omega*C[i][j];
matrixac[i+N][j] = omega*C[i][j];
}
}
// Compute the small signal response
var solac = solve_linear_system(matrixac);
// Save just the magnitude for now
for (var i = this.N - 1; i >= 0; --i) {
var mag = Math.sqrt(solac[i]*solac[i] + solac[i+N]*solac[i+N]);
response[i].push(mag);
}
f *= delta_f; // increment frequency
}
// create solution dictionary
var result = new Array();
for (var name in this.node_map) {
var index = this.node_map[name];
result[name] = (index == -1) ? 0 : response[index];
}
result['frequencies'] = response[this.N];
return result;
}
// Helper for adding devices to a circuit, warns on duplicate device names.
Circuit.prototype.add_device = function(d,name) {
// Add device to list of devices and to device map
this.devices.push(d);
if (name) {
if (this.device_map[name] === undefined)
this.device_map[name] = d;
else {
alert('Warning: two circuit elements share the same name ' + name);
this.device_map[name] = d;
}
}
return d;
}
Circuit.prototype.r = function(n1,n2,v,name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof v) == 'string') {
v = parse_number(v,undefined);
if (v === undefined) return undefined;
}
if (v != 0) {
var d = new Resistor(n1,n2,v);
return this.add_device(d, name);
} else return this.v(n1,n2,0,name); // zero resistance == 0V voltage source
}
Circuit.prototype.d = function(n1,n2,area,name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof area) == 'string') {
area = parse_number(area,undefined);
if (area === undefined) return undefined;
}
if (area != 0) {
var d = new Diode(n1,n2,area);
return this.add_device(d, name);
} // zero area diodes discarded.
}
Circuit.prototype.c = function(n1,n2,v,name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof v) == 'string') {
v = parse_number(v,undefined);
if (v === undefined) return undefined;
}
var d = new Capacitor(n1,n2,v);
return this.add_device(d, name);
}
Circuit.prototype.l = function(n1,n2,v,name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof v) == 'string') {
v = parse_number(v,undefined);
if (v === undefined) return undefined;
}
var branch = this.node(undefined,T_CURRENT);
var d = new Inductor(n1,n2,branch,v);
return this.add_device(d, name);
}
Circuit.prototype.v = function(n1,n2,v,name) {
var branch = this.node(undefined,T_CURRENT);
var d = new VSource(n1,n2,branch,v);
return this.add_device(d, name);
}
Circuit.prototype.i = function(n1,n2,v,name) {
var d = new ISource(n1,n2,v);
return this.add_device(d, name);
}
Circuit.prototype.n = function(d,g,s, ratio, name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof ratio) == 'string') {
ratio = parse_number(ratio,undefined);
if (ratio === undefined) return undefined;
}
var d = new Fet(d,g,s,ratio,name,'n');
return this.add_device(d, name);
}
Circuit.prototype.p = function(d,g,s, ratio, name) {
// try to convert string value into numeric value, barf if we can't
if ((typeof ratio) == 'string') {
ratio = parse_number(ratio,undefined);
if (ratio === undefined) return undefined;
}
var d = new Fet(d,g,s,ratio,name,'p');
return this.add_device(d, name);
}
///////////////////////////////////////////////////////////////////////////////
//
// Support for creating and solving a system of linear equations
//
////////////////////////////////////////////////////////////////////////////////
// model circuit using a linear system of the form Ax = b where
// A is an nxn matrix of conductances and branch voltages
// b is an n-element vector of sources
// x is an n-element vector of unknowns (node voltages, branch currents)
// Knowns (A and b) are stored in an augmented matrix M = [A | b]
// Matrix is stored as an array of arrays: M[row][col].
// set augmented matrix to zero
Circuit.prototype.initialize_linear_system = function() {
for (var i = this.N - 1; i >= 0; --i) {
var row = this.matrix[i];
for (var j = this.N; j >= 0; --j) // N+1 entries
row[j] = 0;
}
}
// Allocate an NxM matrix
Circuit.prototype.make_mat = function(N,M) {
var mat = new Array(N);
for (var i = N - 1; i >= 0; --i) {
mat[i] = new Array(M);
for (var j = M - 1; j >= 0; --j) {
mat[i][j] = 0.0;
}
}
return mat;
}
// Form b = scale*Mx
Circuit.prototype.matv_mult = function(M,x,b,scale) {
var n = M.length;
var m = M[0].length;
if (n != b.length || m != x.length)
{ throw 'Rows of M mismatched to b or cols mismatch to x.';
}
for (var i = 0; i < n; i++)
{
var temp = 0;
for (var j = 0; j < m; j++)
{
temp += M[i][j]*x[j];
}
b[i] = scale*temp; // Recall the neg in the name
}
}
// Form C = A + scale*B
Circuit.prototype.mat_scale_add = function(A, B, scale, C) {
var n = A.length;
var m = A[0].length;
if (n > B.length || m > B[0].length)
{ throw 'Row or columns of A to large for B';
}
if (n > C.length || m > C[0].length)
{ throw 'Row or columns of A to large for C';
}
for (var i = 0; i < n; i++)
{
for (var j = 0; j < m; j++)
{
C[i][j] = A[i][j] + scale * B[i][j];
}
}
}
// Copy A -> using the bounds of A
Circuit.prototype.copy_mat = function(src,dest) {
var n = src.length;
var m = src[0].length;
if (n > dest.length || m > dest[0].length)
{ throw 'Rows or cols > rows or cols of dest';
}
for (var i = 0; i < n; i++)
{
for (var j = 0; j < m; j++)
{
dest[i][j] = src[i][j];
}
}
}
// add val component between two nodes to matrix M
// Index of -1 refers to ground node
Circuit.prototype.add_two_terminal = function(i,j,g,M) {
if (i >= 0) {
M[i][i] += g;
if (j >= 0) {
M[i][j] -= g;
M[j][i] -= g;
M[j][j] += g;
}
} else if (j >= 0)
M[j][j] += g;
}
// add val component between two nodes to matrix M
// Index of -1 refers to ground node
Circuit.prototype.get_two_terminal = function(i,j,x) {
var xi_minus_xj = 0;
if (i >= 0) xi_minus_xj = x[i];
if (j >= 0) xi_minus_xj -= x[j];
return xi_minus_xj
}
Circuit.prototype.add_conductance_l = function(i,j,g) {
this.add_two_terminal(i,j,g, this.Gl)
}
Circuit.prototype.add_conductance = function(i,j,g) {
this.add_two_terminal(i,j,g, this.G)
}
Circuit.prototype.add_capacitance = function(i,j,c) {
this.add_two_terminal(i,j,c,this.C)
}
// add individual conductance to Gl matrix
Circuit.prototype.add_to_Gl = function(i,j,g) {
if (i >=0 && j >= 0)
this.Gl[i][j] += g;
}
// add individual conductance to Gl matrix
Circuit.prototype.add_to_G = function(i,j,g) {
if (i >=0 && j >= 0)
this.G[i][j] += g;
}
// add individual capacitance to C matrix
Circuit.prototype.add_to_C = function(i,j,c) {
if (i >=0 && j >= 0)
this.C[i][j] += c;
}
// add source info to rhs
Circuit.prototype.add_to_rhs = function(i,v,rhs) {
if (i >= 0) rhs[i] += v;
}
// solve Ax=b and return vector x given augmented matrix M = [A | b]
// Uses Gaussian elimination with partial pivoting
function solve_linear_system(M,rhs) {
var N = M.length; // augmented matrix M has N rows, N+1 columns
var temp,i,j;
// Copy the rhs in to the last column of M if one is given.
if (rhs != null) {
for (var row = 0; row < N ; row++) {
M[row][N] = rhs[row];
}
}
// gaussian elimination
for (var col = 0; col < N ; col++) {
// find pivot: largest abs(v) in this column of remaining rows
var max_v = Math.abs(M[col][col]);
var max_col = col;
for (i = col + 1; i < N; i++) {
temp = Math.abs(M[i][col]);
if (temp > max_v) { max_v = temp; max_col = i; }
}
// if no value found, generate a small conductance to gnd
// otherwise swap current row with pivot row
if (max_v == 0) M[col][col] = 1e-10;
else {
temp = M[col];
M[col] = M[max_col];
M[max_col] = temp;
}
// now eliminate this column for all subsequent rows
for (i = col + 1; i < N; i++) {
temp = M[i][col]/M[col][col]; // multiplier we'll use for current row
if (temp != 0)
// subtract current row from row we're working on
// remember to process b too!
for (j = col; j <= N; j++) M[i][j] -= M[col][j]*temp;
}
}
// matrix is now upper triangular, so solve for elements of x starting
// with the last row
var x = new Array(N);
for (i = N-1; i >= 0; --i) {
temp = M[i][N]; // grab b[i] from augmented matrix as RHS
// subtract LHS term from RHS using known x values
for (j = N-1; j > i; --j) temp -= M[i][j]*x[j];
// now compute new x value
x[i] = temp/M[i][i];
}
// return solution
return x;
}
// test solution code, expect x = [2,3,-1]
//M = [[2,1,-1,8],[-3,-1,2,-11],[-2,1,2,-3]];
//x = solve_linear_system(M);
//y = 1; // so we have place to set a breakpoint :)
///////////////////////////////////////////////////////////////////////////////
//
// Device base class
//
////////////////////////////////////////////////////////////////////////////////
function Device() {
}
// complete initial set up of device
Device.prototype.finalize = function() {
}
// Load the linear elements in to Gl and C
Device.prototype.load_linear = function(ckt) {
}
// load linear system equations for dc analysis
// (inductors shorted and capacitors opened)
Device.prototype.load_dc = function(ckt,soln,rhs) {
}
// load linear system equations for tran analysis
Device.prototype.load_tran = function(ckt,soln) {
}
// load linear system equations for ac analysis:
// current sources open, voltage sources shorted
// linear models at operating point for everyone else
Device.prototype.load_ac = function(ckt,rhs) {
}
// return time of next breakpoint for the device
Device.prototype.breakpoint = function(time) {
return undefined;
}
///////////////////////////////////////////////////////////////////////////////
//
// Parse numbers in engineering notation
//
///////////////////////////////////////////////////////////////////////////////
// convert first character of argument into an integer
function ord(ch) {
return ch.charCodeAt(0);
}
// convert string argument to a number, accepting usual notations
// (hex, octal, binary, decimal, floating point) plus engineering
// scale factors (eg, 1k = 1000.0 = 1e3).
// return default if argument couldn't be interpreted as a number
function parse_number(s,default_v) {
s = s.toLowerCase(); // make life simple for ourselves
var slen = s.length;
var multiplier = 1;
var result = 0;
var index = 0;
// skip leading whitespace
while (index < slen && s.charAt(index) <= ' ') index += 1;
if (index == slen) return default_v;
// check for leading sign
if (s.charAt(index) == '-') {
multiplier = -1;
index += 1;
} else if (s.charAt(index) == '+')
index += 1;
var start = index; // remember where digits start
// if leading digit is 0, check for hex, octal or binary notation
if (index >= slen) return default_v;
else if (s.charAt(index) == '0') {
index += 1;
if (index >= slen) return 0;
if (s.charAt(index) == 'x') { // hex
while (true) {
index += 1;
if (index >= slen) break;
if (s.charAt(index) >= '0' && s.charAt(index) <= '9')
result = result*16 + ord(s.charAt(index)) - ord('0');
else if (s.charAt(index) >= 'a' && s.charAt(index) <= 'f')
result = result*16 + ord(s.charAt(index)) - ord('a') + 10;
else break;
}
return result*multiplier;
} else if (s.charAt(index) == 'b') { // binary
while (true) {
index += 1;
if (index >= slen) break;
if (s.charAt(index) >= '0' && s.charAt(index) <= '1')
result = result*2 + ord(s.charAt(index)) - ord('0');
else break;
}
return result*multiplier;
} else if (s.charAt(index) != '.') { // octal
while (true) {
if (s.charAt(index) >= '0' && s.charAt(index) <= '7')
result = result*8 + ord(s.charAt(index)) - ord('0');
else break;
index += 1;
if (index >= slen) break;
}
return result*multiplier;
}
}
// read decimal integer or floating-point number
while (true) {
if (s.charAt(index) >= '0' && s.charAt(index) <= '9')
result = result*10 + ord(s.charAt(index)) - ord('0');
else break;
index += 1;
if (index >= slen) break;
}
// fractional part?
if (index < slen && s.charAt(index) == '.') {
while (true) {
index += 1;
if (index >= slen) break;
if (s.charAt(index) >= '0' && s.charAt(index) <= '9') {
result = result*10 + ord(s.charAt(index)) - ord('0');
multiplier *= 0.1;
} else break;
}
}
// if we haven't seen any digits yet, don't check
// for exponents or scale factors
if (index == start) return default_v;
// type of multiplier determines type of result:
// multiplier is a float if we've seen digits past
// a decimal point, otherwise it's an int or long.
// Up to this point result is an int or long.
result *= multiplier;
// now check for exponent or engineering scale factor. If there
// is one, result will be a float.
if (index < slen) {
var scale = s.charAt(index);
index += 1;
if (scale == 'e') {
var exponent = 0;
multiplier = 10.0;
if (index < slen) {
if (s.charAt(index) == '+') index += 1;
else if (s.charAt(index) == '-') {
index += 1;
multiplier = 0.1;
}
}
while (index < slen) {
if (s.charAt(index) >= '0' && s.charAt(index) <= '9') {
exponent = exponent*10 + ord(s.charAt(index)) - ord('0');
index += 1;
} else break;
}
while (exponent > 0) {
exponent -= 1;
result *= multiplier;
}
} else if (scale == 't') result *= 1e12;
else if (scale == 'g') result *= 1e9;
else if (scale == 'k') result *= 1e3;
else if (scale == 'u') result *= 1e-6;
else if (scale == 'n') result *= 1e-9;
else if (scale == 'p') result *= 1e-12;
else if (scale == 'f') result *= 1e-15;
else if (scale == 'm') {
if (index+1 < slen) {
if (s.charAt(index) == 'e' && s.charAt(index+1) == 'g')
result *= 1e6;
else if (s.charAt(index) == 'i' && s.charAt(index+1) == 'l')
result *= 25.4e-6;
} else result *= 1e-3;
}
}
// ignore any remaining chars, eg, 1kohms returns 1000
return result;
}
Circuit.prototype.parse_number = parse_number; // make it easy to call from outside
///////////////////////////////////////////////////////////////////////////////
//
// Sources
//
///////////////////////////////////////////////////////////////////////////////
// argument is a string describing the source's value:
// <value> or dc(<value>) -- constant value
// pulse(<vinit>,<vpulse>,<tdelay>,<trise>,<tfall>,<t_width>,<t_period>)
// sin(<voffset>,<vamplitude>,<hz>,<tdelay>,<phase_offset_degrees>)
// pwl(<time>,<value>,...) -- piecewise linear: time,value pairs
// returns an object with the following attributes:
// value(t) -- compute source value at time t
// inflection_point(t) -- compute time after t when a time point is needed
// dc -- value at time 0
function parse_source(v) {
// generic parser: parse v as either <value> or <fun>(<value>,...)
var src = new Object();
src.value = function(t) { return 0; } // overridden below
src.inflection_point = function(t) { return undefined; }; // may be overridden below
// see if there's a "(" in the description
var index = v.indexOf('(');
var ch;
if (index >= 0) {
src.fun = v.slice(0,index); // function name is before the "("
src.args = []; // we'll push argument values onto this list
var end = v.indexOf(')',index);
if (end == -1) end = v.length;
index += 1; // start parsing right after "("
while (index < end) {
// figure out where next argument value starts
ch = v.charAt(index);
if (ch <= ' ') { index++; continue; }
// and where it ends
var arg_end = v.indexOf(',',index);
if (arg_end == -1) arg_end = end;
// parse and save result in our list of arg values
src.args.push(parse_number(v.slice(index,arg_end),undefined));
index = arg_end + 1;
}
} else {
src.fun = 'dc';
src.args = [parse_number(v,0)];
}
// post-processing for constant sources
if (src.fun == 'dc') {
var value = src.args[0];
if (value === undefined) value = 0;
src.value = function(t) { return value; } // closure
}
// post-processing for pulsed sources
else if (src.fun == 'pulse') {
var v1 = arg_value(src.args,0,0); // default init value: 0V
var v2 = arg_value(src.args,1,1); // default plateau value: 1V
var td = Math.min(0,arg_value(src.args,2,0)); // time pulse starts
var tr = Math.abs(arg_value(src.args,3,1e-9)); // default rise time: 1ns
var tf = Math.abs(arg_value(src.args,4,1e-9)); // default rise time: 1ns
var pw = Math.abs(arg_value(src.args,5,1e9)); // default pulse width: "infinite"
var per = Math.abs(arg_value(src.args,6,1e9)); // default period: "infinite"
var t1 = td; // time when v1 -> v2 transition starts
var t2 = t1 + tr; // time when v1 -> v2 transition ends
var t3 = t2 + pw; // time when v2 -> v1 transition starts
var t4 = t3 + tf; // time when v2 -> v1 transition ends
// return value of source at time t
src.value = function(t) { // closure
var tmod = Math.fmod(t,per);
if (tmod < t1) return v1;
else if (tmod < t2) return v1 + (v2-v1)*(tmod-t1)/(t2-t1);
else if (tmod < t3) return v2;
else if (tmod < t4) return v2 + (v1-v2)*(tmod-t3)/(t4-t3);
else return v1;
}
// return time of next inflection point after time t
src.inflection_point = function(t) { // closure
var tstart = per * Math.floor(t/per);
var tmod = t - tstart;
if (tmod < t1) return tstart + t1;
else if (t < t2) return tstart + t2;
else if (t < t3) return tstart + t3;
else if (t < t4) return tstart + t4;
else return tstart + per + t1;
}
}
// post-processing for sinusoidal sources
else if (src.fun == 'sin') {
var degrees_to_radians = 2*Math.PI/360.0;
var voffset = arg_value(src.args,0,0); // default offset voltage: 0V
var va = arg_value(src.args,1,1); // default amplitude: -1V to 1V
var freq = arg_value(src.args,2,1); // default frequency: 1Hz
var td = Math.min(0,arg_value(src.args,3,0)); // default time delay: 0sec
var phase = arg_value(src.args,4,0); // default phase offset: 0 degrees
phase /= 360.0;
// return value of source at time t
src.value = function(t) { // closure
if (t < td) return voffset + va*Math.sin(2*Math.PI*phase);
else {
t -= td;
return voffset + va*Math.sin(2*Math.PI*(freq*(t - td) + phase));
}
}
// return time of next inflection point after time t
src.inflection_point = function(t) { // closure
if (t < td) return td;
else return undefined;
}
}
// to do:
// post-processing for piece-wise linear sources
// object has all the necessary info to compute the source value and inflection points
src.dc = src.value(0); // DC value is value at time 0
return src;
}
// helper function: return args[index] if present, else default_v
function arg_value(args,index,default_v) {
if (index < args.length) {
var result = args[index];
if (result === undefined) result = default_v;
return result;
} else return default_v;
}
// we need fmod in the Math library!
Math.fmod = function(numerator,denominator) {
var quotient = Math.floor(numerator/denominator);
return numerator - quotient*denominator;
}
///////////////////////////////////////////////////////////////////////////////
//
// Sources
//
///////////////////////////////////////////////////////////////////////////////
function VSource(npos,nneg,branch,v) {
Device.call(this);
this.src = parse_source(v);
this.npos = npos;
this.nneg = nneg;
this.branch = branch;
}
VSource.prototype = new Device();
VSource.prototype.constructor = VSource;
// load linear part for source evaluation
VSource.prototype.load_linear = function(ckt) {
// MNA stamp for independent voltage source
ckt.add_to_Gl(this.branch,this.npos,1.0);
ckt.add_to_Gl(this.branch,this.nneg,-1.0);
ckt.add_to_Gl(this.npos,this.branch,1.0);
ckt.add_to_Gl(this.nneg,this.branch,-1.0);
}
// Source voltage added to b.
VSource.prototype.load_dc = function(ckt,soln,rhs) {
ckt.add_to_rhs(this.branch,this.src.dc,rhs);
}
// Load time-dependent value for voltage source for tran
VSource.prototype.load_tran = function(ckt,soln,rhs,time) {
ckt.add_to_rhs(this.branch,this.src.value(time),rhs);
}
// return time of next breakpoint for the device
VSource.prototype.breakpoint = function(time) {
return this.src.inflection_point(time);
}
// small signal model ac value
VSource.prototype.load_ac = function(ckt,rhs) {
ckt.add_to_rhs(this.branch,1.0,rhs);
}
function ISource(npos,nneg,v) {
Device.call(this);
this.src = parse_source(v);
this.npos = npos;
this.nneg = nneg;
}
ISource.prototype = new Device();
ISource.prototype.constructor = ISource;
// load linear system equations for dc analysis
ISource.prototype.load_dc = function(ckt,soln,rhs) {
var is = this.src.dc;
// MNA stamp for independent current source
ckt.add_to_rhs(this.npos,-is,rhs); // current flow into npos
ckt.add_to_rhs(this.nneg,is,rhs); // and out of nneg
}
// load linear system equations for tran analysis (just like DC)
ISource.prototype.load_tran = function(ckt,soln,rhs,time) {
var is = this.src.value(time);
// MNA stamp for independent current source
ckt.add_to_rhs(this.npos,-is,rhs); // current flow into npos
ckt.add_to_rhs(this.nneg,is,rhs); // and out of nneg
}
// return time of next breakpoint for the device
ISource.prototype.breakpoint = function(time) {
return this.src.inflection_point(time);
}
// small signal model: open circuit
ISource.prototype.load_ac = function(ckt) {
// MNA stamp for independent current source
ckt.add_to_rhs(this.npos,-1.0,rhs); // current flow into npos
ckt.add_to_rhs(this.nneg,1.0,rhs); // and out of nneg
}
///////////////////////////////////////////////////////////////////////////////
//
// Resistor
//
///////////////////////////////////////////////////////////////////////////////
function Resistor(n1,n2,v) {
Device.call(this);
this.n1 = n1;
this.n2 = n2;
this.g = 1.0/v;
}
Resistor.prototype = new Device();
Resistor.prototype.constructor = Resistor;
Resistor.prototype.load_linear = function(ckt) {
// MNA stamp for admittance g
ckt.add_conductance_l(this.n1,this.n2,this.g);
}
Resistor.prototype.load_dc = function(ckt) {
// Nothing to see here, move along.
}
Resistor.prototype.load_tran = function(ckt,soln) {
}
Resistor.prototype.load_ac = function(ckt) {
}
///////////////////////////////////////////////////////////////////////////////
//
// Diode
//
///////////////////////////////////////////////////////////////////////////////
function Diode(n1,n2,v) {
Device.call(this);
this.anode = n1;
this.cathode = n2;
this.area = v;
this.is = 1.0e-14;
this.ais = this.area * this.is;
this.vt = 2.58e-2; // 26 millivolts
}
Diode.prototype = new Device();
Diode.prototype.constructor = Diode;
Diode.prototype.load_linear = function(ckt) {
// Diode is not linear, has no linear piece.
}
Diode.prototype.load_dc = function(ckt,soln,rhs) {
var vd = ckt.get_two_terminal(this.anode, this.cathode, soln);
var temp1 = this.ais * Math.exp(vd / this.vt);
var id = temp1 - this.ais;
var gd = temp1 / this.vt
// MNA stamp for independent current source
ckt.add_to_rhs(this.anode,-id,rhs); // current flows into anode
ckt.add_to_rhs(this.cathode,id,rhs); // and out of cathode
ckt.add_conductance(this.anode,this.cathode,gd);
}
Diode.prototype.load_tran = function(ckt,soln,rhs,time) {
this.load_dc(ckt,soln,rhs);
}
Diode.prototype.load_ac = function(ckt) {
}
///////////////////////////////////////////////////////////////////////////////
//
// Capacitor
//
///////////////////////////////////////////////////////////////////////////////
function Capacitor(n1,n2,v) {
Device.call(this);
this.n1 = n1;
this.n2 = n2;
this.value = v;
}
Capacitor.prototype = new Device();
Capacitor.prototype.constructor = Capacitor;
Capacitor.prototype.load_linear = function(ckt) {
// MNA stamp for capacitance matrix
ckt.add_capacitance(this.n1,this.n2,this.value);
}
Capacitor.prototype.load_dc = function(ckt,soln,rhs) {
}
Capacitor.prototype.load_ac = function(ckt) {
}
Capacitor.prototype.load_tran = function(ckt) {
}
///////////////////////////////////////////////////////////////////////////////
//
// Inductor
//
///////////////////////////////////////////////////////////////////////////////
function Inductor(n1,n2,branch,v) {
Device.call(this);
this.n1 = n1;
this.n2 = n2;
this.branch = branch;
this.value = v;
}
Inductor.prototype = new Device();
Inductor.prototype.constructor = Inductor;
Inductor.prototype.load_linear = function(ckt) {
// MNA stamp for inductor linear part
// L on diag of C because L di/dt = v(n1) - v(n2)
ckt.add_to_Gl(this.n1,this.branch,1);
ckt.add_to_Gl(this.branch,this.n1,1);
ckt.add_to_Gl(this.n2,this.branch,-1);
ckt.add_to_Gl(this.branch,this.n2,-1);
ckt.add_to_C(this.branch,this.branch,this.value)
}
Inductor.prototype.load_dc = function(ckt,soln,rhs) {
// Inductor is a short at dc, so is linear.
}
Inductor.prototype.load_ac = function(ckt) {
}
Inductor.prototype.load_tran = function(ckt) {
}
///////////////////////////////////////////////////////////////////////////////
//
// Simplified MOS FET with no bulk connection and no body effect.
//
///////////////////////////////////////////////////////////////////////////////
function Fet(d,g,s,ratio,name,type) {
Device.call(this);
this.d = d;
this.g = g;
this.s = s;
this.name = name;
this.ratio = ratio;
if (type != 'n' && type != 'p')
{ throw 'fet type is not n or p';
}
this.type_sign = (type == 'n') ? 1 : -1;
this.vt = 0.5;
this.kp = 20e-6;
this.beta = this.kp * this.ratio;
this.lambda = 0.05;
}
Fet.prototype = new Device();
Fet.prototype.constructor = Fet;
Fet.prototype.load_linear = function(ckt) {
// FET's are nonlinear, just like javascript progammers
}
Fet.prototype.load_dc = function(ckt,soln,rhs) {
var vds = this.type_sign * ckt.get_two_terminal(this.d, this.s, soln);
if (vds < 0) { // Drain and source have swapped roles
var temp = this.d;
this.d = this.s;
this.s = temp;
vds = this.type_sign * ckt.get_two_terminal(this.d, this.s, soln);
}
var vgs = this.type_sign * ckt.get_two_terminal(this.g, this.s, soln);
var vgst = vgs - this.vt;
with (this) {
var gmgs,ids,gds;
if (vgst > 0.0 ) { // vgst < 0, transistor off, no subthreshold here.
if (vgst < vds) { /* Saturation. */
gmgs = beta * (1 + (lambda * vds)) * vgst;
ids = type_sign * 0.5 * gmgs * vgst;
gds = 0.5 * beta * vgst * vgst * lambda;
} else { /* Linear region */
gmgs = beta * (1 + lambda * vds);
ids = type_sign * gmgs * vds * (vgst - 0.50 * vds);
gds = gmgs * (vgst - vds) + beta * lambda * vds * (vgst - 0.5 * vds);
gmgs *= vds;
}
ckt.add_to_rhs(d,-ids,rhs); // current flows into the drain
ckt.add_to_rhs(s, ids,rhs); // and out the source
ckt.add_conductance(d,s,gds);
ckt.add_to_G(s,s, gmgs);
ckt.add_to_G(d,s,-gmgs);
ckt.add_to_G(d,g, gmgs);
ckt.add_to_G(s,g,-gmgs);
}
}
}
Fet.prototype.load_tran = function(ckt,soln,rhs) {
this.load_dc(ckt,soln,rhs);
}
Fet.prototype.load_ac = function(ckt) {
}
///////////////////////////////////////////////////////////////////////////////
//
// Module definition
//
///////////////////////////////////////////////////////////////////////////////
var module = {
'Circuit': Circuit,
'parse_number': parse_number,
}
return module;
}());
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