SPICE circuit solvers

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SPICE circuit solvers

• By Martin Gustafsson (Ph. D. Student)
• Supervisor Jonas Ekman

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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Introduction (1 of 2)

• Circuits become more difficult to analyze
• Advanced models for electronic components
• Large nets of electronic components
• Electronic Design Aids
• Oldschool Nothing into simulator without
  hand-calc.
• Newschool Simulator an aid, even in design
• Noise estimation difficult

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Introduction (2 of 2)

• Industry
• Short deadlines
• First-time-right
• Research
• Time is money, even here
• Can I trust the results from the simulator?

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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How does a circuit solver work? (1 of 5)

• Needs to be understood to asses the accuracy
• Analysis modes
• AC
• DC
• Transient
• Fundamentaly similar

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How does a circuit solver work? (2 of 5)

• N-node circuit generalized to N-port
• One port represents each node
• Nodal analysis
• Admittance matrix is defined for the N-port
• IYV
• Y-1 is found to get VY-1I

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How does a circuit solver work? (3 of 5)

• How is the Admittance matrix built?
• Represented by 2-Port
• Derive on whiteboard for V1 and V2
• Resistor R gt YR1/R
• Inductor L gt YL1/(jwL)

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How does a circuit solver work? (4 of 5)

• Admittances are depending on what component
• Admittances are depending on analysis mode
• YC (AC)jwC
• YC(DC) 0
• Transient implies diff. equ i(t)i0(t)CdV/dt
• Solution need to converge at each timestep

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How does a circuit solver work? (5 of 5)

• Non-linear components
• Convergence in AC and DC
• Diode current
• How are different analysis made?

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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Analyses modes (1 of 4)

• AC
• Frequency analysis
• Estimate BW, Noise, Gain, Attenuation
• DC
• Operating point analysis
• Estimate bias points, static current
• Transient analysis
• Time domain behaviour of a circuit
• Evaluate performance

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Analyses modes (2 of 4)

• AC analysis
• Build Admittance matrix for DC
• Find Bias points
• Build Admittance matrix for each frequency
• Find convergence for non-linear components
• Find Y-1 and solve for V

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Analysis modes (3 of 4)

• DC analysis
• Build admittance matrix for starting point
• Build Admittance matrix for all swept DC points
• Find convergence for non-linear components
• Find Y-1 and solve for V

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Analysis modes (4 of 4)

• Transient analysis
• Build DC admittance matrix for starting point
• Find DC bias point
• Build admittance matrix for each time instance
• Find convergence for non-linear components
• Find Y-1 and solve for V

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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NA vs. Modified NA (1 of 3)

• Nodal Analysis has been covered
• Simple
• Powerful
• Cannot implement ideal L and ideal V
• Modified Nodal Analysis introduced by Ho -75

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NA vs. MNA (2 of 3)

• Modified Nodal Analysis
• Use the Admittance Matrix
• Also Branch Relations
• Show for circuit example

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NA vs. MNA (3 of 3)

• More relations can be expressed
• Voltage sources
• Initial conditions for diff. equ.
• More powerful

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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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Simulation results (1 of 4)

• A circuit solver was designed
• PETSc matrix package
• Implemented in C
• 2500 lines of code
• NA based solver
• Some results from this solver

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Simulation results (2 of 4)
Circuit

• AC analysis

MGSIM
PSPICE
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Simulation results (3 of 4)
Circuit

• DC analysis

PSPICE
MGSIM
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Simulation results (4 of 4)
Circuit

• Transient analysis

PSPICE
MGSIM
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This seminar

• Introduction
• How does a circuit solver work?
• Analyses modes (AC, DC and transient)
• Nodal Analysis versus Modified Nodal Analysis
• Simulation results
• Conclusion

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Conclusion

• Introduction to Circuit solvers
• How they work
• Different analysis modes
• Modified Nodal Analysis
• Results from Circuit solver design
• Design is cumbersome

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Questions?