The Qstar simulator

1
The Qstar simulator

• Stephan Houben

2
Overview of talk

• Motivation for Qstar
• What can it do?
• Who needs it?
• Useful future extensions
• Conclusions

3
Motivation for Qstar

• Circuit equations have the structure
• However, simulators as Spice, Pstar do not
• explicitly form the circuit equations.

4
Structure of e.g. SPICE, Pstar
input file
Circuit description
Circuit state x
Evaluation
Vectors j(x), q(x), matrices G(x), C(x)
Solver
5
Problems for mathematician

• Circuit equations not explicitly available
• One cannot easily play with the equations in
  e.g. MATLAB/Mathematica
  
• Pstar only provides what is needed for existing
  methods. E.g. implementing Rosenbrock-Wanner
  methods requires
  

6
What does Qstar do?

• Basic idea is similar to Lex/Yacc tools.
• Qstar reads a .pstar file and generates the
  circuit equations explicitly.
  
• It then outputs these equations in an arbitrary
  output format (MATLAB, C, LaTeX,).
  
• Qstar itself doesnt do any numerical computation.

7
Structure of Qstar
input file
Qstar
MATLAB file
LaTeX file
C file
C program by user
Compile run
Results
8
Qstar output formats

• /home/houbenqstar2 -h formats
• This is Qstar2, the multi-format circuit equation
  assembler.
  
• c) 1999, Stephan Houben
• The following formats are supported
• octave -- "Native" Octave output format
  (default).
  
• octavecpp -- C code usable by Octave.
• dassl -- Output format for the DASSL solver
  in Octave.
  
• fsolve -- Output format for Octave's fsolve'
  function.
  
• latex -- LaTeX output format.
• matlab -- Matlab output format.
• numlab -- C code usable by NumLab.
• ocaml -- Objective Caml code.
• scheme -- code for Scheme
• sanecpp -- C code usable by the Sane Vector
  Library
  
• daecpp -- C subclass from DAE class, usable
  by the Sane Vector Library

9
Example circuit
10
Input file
Title Test circuit 6 / Typical simulation ti
me scale t 0, 1.5e-3 / / To start up set
vn(1) 1 at t 0. / include "transistor.pst
ar" circuit e_1(0,5) 10 r_1(0,2) 12k
r_2(2,5) 8.1k l_1(0,3) 0.01 r_3(3,4)
3 c_1(0,1) 0.1u c_2(1,4) 47n transi
stor_1(4,2,1) r_4(1,5) 1.5k end
11
Circuit equations
12
Resulting MATLAB file

• if exist('x')
• x zeros(7, 1)
• end
• if exist('t')
• t 0
• end
• j zeros(7, 1)
• j(1)(((- ((1e-15(exp(min(((x(2)-
  x(1))/0.025),52.0))max(((x(2)-
  x(1))/0.025)-51.0,1)- 1))/10)- (1e-15(exp(min(((x
  (2)- x(1))/0.025),52.0))max(((x(2)-
  x(1))/0.025)-51.0,1)- 1)))(1e-15(exp(min(((x(2)-
  x(4))/0.025),52.0))max(((x(2)-
  x(4))/0.025)-51.0,1)- 1)))((x(1)-
  x(5))/1500.0))
• j(2)(((- (- x(2)/12000.0)((x(2)-
  x(5))/8100.0))((1e-15(exp(min(((x(2)-
  x(4))/0.025),52.0))max(((x(2)-
  x(4))/0.025)-51.0,1)- 1))/10))((1e-15(exp(min(((
  x(2)- x(1))/0.025),52.0))max(((x(2)-
  x(1))/0.025)-51.0,1)- 1))/10))
• j(3)(- x(7)((x(3)- x(4))/3))
• j(4)(((- ((x(3)- x(4))/3)- ((1e-15(exp(min(((x(2
  )- x(4))/0.025),52.0))max(((x(2)-
  x(4))/0.025)-51.0,1)- 1))/10))(1e-15(exp(min(((x
  (2)- x(1))/0.025),52.0))max(((x(2)-
  x(1))/0.025)-51.0,1)- 1)))- (1e-15(exp(min(((x(2)
  - x(4))/0.025),52.0))max(((x(2)-
  x(4))/0.025)-51.0,1)- 1)))
• j(5)((- x(6)- ((x(2)- x(5))/8100.0))- ((x(1)-
  x(5))/1500.0))
  
• j(6)(- x(5)- 10)
• j(7)- x(3)
• q zeros(7, 1)
• .
• .
• .

13
Resulting C file

• void evalCircuit(double t, const Vector x,
  Vector j, Vector q, Matrix G, Matrix C)
  
• j.resize(7)
• j.fill(0)
• j(0)(((- ((1e-15(((((x(1)- x(0))/0.025) 52.0)?(exp(((x(1)- x(0))/0.025)))(3.83100800072e
  22(((x(1)- x(0))/0.025) - 51.0)))- 1))/10)-
  (1e-15(((((x(1)- x(0))/0.025) 52.0)?(exp(((x(1)- x(0))/0.025)))(3.83100800072e
  22(((x(1)- x(0))/0.025) - 51.0)))-
  1)))(1e-15(((((x(1)- x(3))/0.025) 52.0)?(exp(((x(1)- x(3))/0.025)))(3.83100800072e
  22(((x(1)- x(3))/0.025) - 51.0)))- 1)))((x(0)-
  x(4))/1500.0))
• j(1)(((- (- x(1)/12000.0)((x(1)-
  x(4))/8100.0))((1e-15(((((x(1)- x(3))/0.025) 52.0)?(exp(((x(1)- x(3))/0.025)))(3.83100800072e
  22(((x(1)- x(3))/0.025) - 51.0)))-
  1))/10))((1e-15(((((x(1)- x(0))/0.025) 52.0)?(exp(((x(1)- x(0))/0.025)))(3.83100800072e
  22(((x(1)- x(0))/0.025) - 51.0)))- 1))/10))
• j(2)(- x(6)((x(2)- x(3))/3))
• j(3)(((- ((x(2)- x(3))/3)- ((1e-15(((((x(1)-
  x(3))/0.025) x(3))/0.025)))(3.83100800072e22(((x(1)-
  x(3))/0.025) - 51.0)))- 1))/10))(1e-15(((((x(1)-
  x(0))/0.025) x(0))/0.025)))(3.83100800072e22(((x(1)-
  x(0))/0.025) - 51.0)))- 1)))- (1e-15(((((x(1)-
  x(3))/0.025) x(3))/0.025)))(3.83100800072e22(((x(1)-
  x(3))/0.025) - 51.0)))- 1)))
• j(4)((- x(5)- ((x(1)- x(4))/8100.0))- ((x(0)-
  x(4))/1500.0))
  
• j(5)(- x(4)- 10)
• j(6)- x(2)
• q.resize(7)
• .
• .
• .

14
Easy to add new output formats

• Qstar has an object-oriented structure.
• Output formats inherit from class Output.
• class LaTeXOutput(output.Output)
• functions
• "exp" "es",
• "log" "\\logs",
• "sin" "\\sins",
• "cos" "\\coss",
• "tan" "\\tans",
• "sqrt" "\\sqrts",
• "neg" "- s",
• def output_time(self)
• return "t"
• def output_variable(self, var, index)
• return "s_d" (var, index1)

15
Limitations of Qstar

• Does not handle the full Pstar language. It
  could be extended, but some things (e.g.
  transient..end blocks) dont make sense
  inQstar.
• Cannot use model libraries in C this limitation
  is intrinsic in the goal to get explicit
  equations.

16
Qstar for templates?

• Since Qstar generates C code for each separate
  circuit, it could be used to produce so-called
  templates.
  
• A template is a dedicated circuit simulator,
  which only handles a single circuit layout but is
  very fast (good for optimisation).
  

17
Useful future extensions

• More models currently there is only one
  transistor-model (Bipolar), by S. Onneweer.
  
• A MOSFET model would be useful.
• More output formats Mathematica might be
  useful.
  

18
Conclusions

• Qstar is useful as a research tool.
• It is where possible compatible with Pstar, but
  full compatibility is probably not possible
  and/or worthwhile.
  
• Qstar is basically finished, but it could benefit
  from some extensions.

19
Future maintenance

• Useful for SCG to keep Qstar available (for
  future students, industry contacts).
  
• Extensions can be implemented on a by need
  basis.