Perform analysis

SLiCAP has 16 predefined analysis types. However, since SLiCAP is built upon the powerful Sympy CAS (Computer Algebra System), users can easily extend SLiCAP’s capabilities and add functionality.

General instruction format

The general instruction format is (with default keyword arguments):

result = do<Instruction>(cir, transfer='gain', source='circuit', detector='circuit',
                         lgref='circuit', convtype=None, pardefs=None, numeric=False,
                         stepdict=None)

where <Instruction> describes the analysis to be performed.

The return value of all instructions is an instrucion object. Execution of the instruction will set some attributes of this object. Detailed information for each instruction is given in de Reference section.

The function arguments are discussed in separate sections below.

The circuit object

cir: circuit object use for the instruction. cir is the only required argument for all instructions.

The transfer type

transfer: None | ‘gain’ | ‘asymptotic’ | ‘loopgain’ | ‘servo’ | ‘direct’; defaults to ‘gain’.

A transfer type is required for transfer related analysis types.

• None: no transfer type is specified; SLiCAP will calculate the detector voltage or current, or perform analysis that do not require a source specification.

• ‘gain’: source to detector transfer

• ‘asymptotic’: Gain of a circuit withthe loop gain reference replaced with a nullor (the ‘asymptotic-gain’); see Work with feedback

• ‘direct’: Gain of a circuit with the value of the loop gain reference set to zero (the ‘direct transfer’); see Work with feedback

• ‘loopgain’: Gain enclosed in the loop involving the loop gain reference (the ‘loop gain’); see Work with feedback

• ‘servo’: \(\frac{-L}{1-L}\), where \(L\) is the loop gain as defined above (the ‘servo function’); see Work with feedback

The signal source

source: None | ‘circuit’ | <refDes> | [<refDes+>, <refDes->], defaults to : ‘circuit’

• None: No source required or desired

• ‘circuit’: SLiCAP uses the source specification from the netlist

• <refDes>, <refDes+>, <refDes->: Name of an independent voltage or current source that must be used as signal source

Important

The circuit object attribute indepVars returns a list with circuit independent sources that can be used as signal source.

import SLiCAP as sl
sl.initProject("my Project")
cir = sl.makeCircuit(<myCircuit>)
# Obtain the list of independent sources in <myCircuit>
print(cir.indepVars)

A signal source specification is required for transfers: ‘gain’, ‘direct’, and ‘asymptotic’.

If a source definition is given, the instructions ‘doNoise()’ and ‘doDCvar()’ also return the source-referred noise and source referred DC variance, respectively.

A signal source can be specified in three different ways:

• On the schematic

  Place a SPICE directive (command) .source on the schematic.

  • The format for a single-ended source is: .source <refdes-independent-source>

  • The format for a differential source is: .source <refdes-positive-source> <refdes-negative-source>

• In the circuit file

  Place the above commands in the netlist (.cir) file

• With the instruction

  This is done by using th keyword argument source in the instruction. The format is as follows

  • Single-ended source: source=<refdes-independent-source>

  • Differential source: source=[<refdes-positive-source>, <refdes-negative-source>]

The signal detector

detector: None | ‘circuit’ | <detName> | [<detName+>, <detName->], defaults to : ‘circuit’

• None: No detector required or desired

• ‘circuit’: SLiCAP uses the detector specification from the netlist

• <detName>, <detName+>, <detName->: Name of a dependent variable (nodal voltage or branch current) that must be used as signal detector

Important

The circuit object method depVars() returns a list with circuit dependent variables that can be used as detector.

import SLiCAP as sl
sl.initProject("my Project")
cir = sl.makeCircuit(<myCircuit>)
# Obtain the list names of dependent variables in <myCircuit>
print(cir.depVars())

A signal detector specification is NOT required for the instructions:

• doMatrix()

• doDenom()

• doPoles()

• doSolve()

• doDCsolve()

• doTimeSolve()

AND for transfer types:

• loopgain

• servo

In all other cases a definition of a detector is required.

A signal detector can be specified in three different ways:

• On the schematic

  Place a SPICE directive (command) .detector on the schematic.

  • The format for a single voltage detector is: .detector V_<node-name>

  • The format for a differential voltage detector is: .detector V_<positive-node>  V_<negative-node>

  • The format for a single current detector is: .detector I_<element-refdes>

  • The format for a differential current detector is: .detector I_<positive-element> I_<negative-element>

• In the circuit file

  Place the above commands in the netlist (.cir) file

• With the instruction

  Use the keyword argument detector in the instruction. The format is as follows

  • Single-ended voltage detector: detector="V_<node-name>"

  • Differential voltage detector: detector=["V_<positive-node>", "V_<negative-node>"]

  • Single-ended current detector: detector="I_<element-refdes>"

  • Differential current detector: detector=["I_<positive-element>", "I_<negative-element>"]

The loop gain reference

lgref: None | ‘circuit’ | <refDes> | [<refDes+>, <refDes->], defaults to : ‘circuit’; see Work with feedback circuits.

• None: No loop gain reference required or desired

• ‘circuit’: SLiCAP uses the loop gain reference specification from the netlist

• <refDes>, <refDes+>, <refDes->: Name of a dependent source (controlled source) that must be used as loop gain reference

Important

The circuit object attribute controlled returns a list with circuit dependent sources that can be used as loop gain reference.

import SLiCAP as sl
sl.initProject("my Project")
cir = sl.makeCircuit(<myCircuit>)
# Obtain the list names of dependent sources in <myCircuit>
print(cir.controlled)

A loop gain reference specification is required for the transfers: ‘asymptotic’, direct’, ‘loopgain’, and ‘servo’; see Work with feedback circuits.

A loop gain reference source can be specified in three different ways:

• On the schematic

  Place a SPICE directive (command) .lgref on the schematic.

  • The format for a single-ended source is: .lgref <refdes-dependent-source>

  • The format for a differential source is: .lgref <refdes-pos-dep-source> <refdes-neg-dep-source>

• In the circuit file

  Place the above commands in the netlist (.cir) file

• With the instruction

  This is done by using the keyword argument lgref in the instruction. The format is as follows

  • Single-ended loop gain reference: lgref="<refdes-dependent-source>"

  • Differential loop gain reference: lgref["<refdes-pos-dep-source>" "<refdes-neg-dep-source>"]

The conversion type

convtype: None | ‘all’ | ‘dd’ | ‘dc’ | ‘cd’ | ‘cc’; defaults to None. See Work with balanced circuits

The conversion type is used to convert balanced circuits into differential-mode and common-mode equivalent networks.

• None: No matrix conversion will be applied

• ‘all’: Dependent variables and independent variables will be grouped in differential-mode and common-mode variables.

  The circuit matrix dimension is not changed.

  This conversion type can only be used with the doMatrix() instruction.

• ‘dd’: After grouping of the vaiables in differential-mode and common-mode variables, only the differential-mode variables of both dependent and independent variables are considered.

  The matrix equation describes the differential-mode behavior of the circuit.

• ‘cc’: After grouping of the vaiables in differential-mode and common-mode variables, only the common-mode variables of both dependent and independent variables are considered.

  The matrix equation describes the common-mode behavior of the circuit.

• ‘dc’: After grouping of the vaiables in differential-mode and common-mode variables, only the differential-mode dependent variables and the common-mode independent variables are considered.

  The matrix equation describes the common-mode to differential-mode conversion of the circuit. This conversion type can only be used with the doMatrix() instruction.

• ‘cd’: After grouping of the vaiables in differential-mode and common-mode variables, only the common-mode dependent variables and the differential-mode independent ariables are considered.

  The matrix equation describes the differential-mode to common-mode conversion of the circuit. This conversion type can only be used with the doMatrix() instruction.

The parameter definitions

pardefs: None | ‘circuit’ | dict; defaults to None

• None: Analysis will be performed without substitution of parameters

• ‘circuit’: Analysis will be performed with all parameters defined with the circuit (cir.parDefs), recursively substituted

• dict: Analysis will be performed with all parameters defined in dict (key = parameter name, value = parameter value or expression)

Example: obtain a dictionary with the circuit parameter definitions and a list with undefined parameters:

import SLiCAP as sl
sl.initProject("my Project")
cir = sl.makeCircuit(<myCircuit>)
# Obtain the parameter definitions in <myCircuit>
for key in cir.parDefs.keys():
    print(key, ':', cir.parDefs[key])
# Print a list with undefined parameters:
print(cir.params)

Conversion to float

numeric: True | False; defaults to False

• False: Analysis results with rational numbers and without numeric evaluation of constants (\(\pi\)) or functions. In some cases, however, pole-zero analysis and noise integration, SLiCAP will switch to floating point calculation.

• True: Analysis results with all constants and functions numerically evaluated and converted to floats.

Parameter stepping

stepdict: None | dict

• None: Analysis will be performed without parameter stepping

• dict: Analysis will be repeated for a number of steps with a different (sets of) parameter(s)

The step dictionary can have the following key-value pairs:

• ‘method’:

  • (str); ‘lin’, ‘log’, ‘list’, ‘array’

• ‘params’:

  • (str, sympy.Symbol) for stepmethod: ‘lin’, ‘log’, and ‘list’

  • (list with str, or sympy.Symbol) for stepmethod: ‘array’

• ‘start’:

  • (float, int, str): start value for ‘lin’ and ‘log’ stepping

• ‘stop’:

  • (float, int, str): stop value for ‘lin’ and ‘log’ stepping

• ‘num’:

  • (int): number of steps for ‘lin’ and ‘log’ stepping

• ‘values’:

  • (list with int, float, or str) step values for stepmethod: ‘list’,

  • (list with lists with int, float, or str) step values for stepmethod: ‘array’

Predefined analysis types

Below an overview of instructions that have been implemented in SLiCAP. Links are provided to the detailed description of the functions in the reference section.

Network equations

doMatrix(): matrix equation of the circuit

Complex frequency domain (Laplace) analysis

doLaplace(): transfer function or detector current/voltage (Laplace expression)

doNumer(): numerator of a transfer function or detector current/voltage

doDenom() : denominator of a transfer function or detector current/voltage

doSolve(): Laplace Transform of the network solution or detector current/voltage

Complex frequency domain analysis: poles and zeros of transfer functions

doPoles(): poles of a transfer, including non-controllable and non-observable (complex frequency solutions of Denom)

doZeros(): zeros of a transfer (complex frequency solutions of Numer)

doPZ(): DC value, poles and zeros of a transfer (with pole-zero canceling: only controllable and observable poles)

Noise analysis

doNoise() returns the spectral densities of the total detector-referred and source-referred noise, and the individual contributions of all independent noise sources.

Time domain analysis: Inverse Laplace Transform

doTime(): detector voltage or current

doImpulse(): unit-impulse response of a transfer

doStep(): unit-step response of a transfer

doTimeSolve(): Time-domain solution of a network

DC (zero-frequency) and DC variance analysis

doDC(): Zero-frequency value of a transfer or detector current/voltage

doDCsolve(): DC network solution

doDCvar(): detector-referred and source-referred DC variance, and the individual contributions of all independent dcvar sources.