ASITIC Documentation: Analysis
| Command Reference | Environmental Variables | Installation | Technology File | Quickstart | Sample Sessions | FAQ |
Aliases: 2port,twoport,2p
Note: This command has been replaced by the 2portx command.Arguments:
This command calculates the 2-Port parameters of a device over a user specified frequency range. The default behavior is to use the pi command in the analysis (the <fast> mode). The <slow> mode uses the pi2 command or if <spiral gnd> is specified, the pi3 command. 2-Port parameters are stored in S format by default, but Y, Z and PI parameters can also be used in polar or rectangular coordinates. The results are stored to <filename> or by default to a file with the same name as the <spiral> name.
Aliases: 2portgnd,twoportgnd,2pg,2pgnd
Note: This command has been replaced by the 2portx.Arguments:
Aliases: 2portpad,twoportpad,2pp
Arguments:
2-Port parameters are stored in S format by default, but other formats can also be used in polar or rectangular coordinates. The results are stored to <filename> or by default to a file with the same name as the <spiral> name.
Aliases: 2porttrans,transs,2pt,2ptrans
Calculate the 2-Port parameters of a spiral using the CalcTrans command over a user-specified frequency range.Arguments:
Aliases: 2portx,twoportx,2px
Arguments:
This command calculates the 2-Port parameters of a device over a user specified frequency range by invoking pix at each frequency. 2-Port parameters are stored in S format by default, but Y, Z and PI parameters can also be used in polar or rectangular coordinates. The results are stored to <filename> or by default to a file with the same name as the <spiral> name.
Aliases: 2pzin,2portzin,twoportzin,2pz
Calculate the input impedance of a two-port when one port is terminated in a complex impedance <ZL>. The results of the previous analysis are used for the calculation.
Arguments:
Aliases: 3port,3p,calc3p,3pcalc
This command will calculate the 3-port circuit parameters for three spirals. Each spiral is excited by placing a source at the head of the spiral and ground at the end of each spiral. The analysis is performed over the specified frequency range.
Arguments:
Aliases: calctrans,ttrans,transt,tt
Arguments:
If no <gnd resistance> parameter is used, then the value of RG=Re(Z12) is only a modeling value which may also be negative. The overall input impedance of the transformer, though, always has a positive real part. If <spiral gnd> is specified, this structure is used as the reference for the ground in the capacitance matrix calculation.
Aliases: cap,capacitance,c,capmat
This command will calculate the capacitance matrix between a group of spirals at a particular frequency. The capacitance is lossy and includes a substrate loss resistance in series with each capacitor.This command is useful for estimating the capacitance of a metal-metal capacitor as well as the substrate loss associated with structures. Equally useful is the ability to predict substrate coupling between metal structures.
To compute the self-capacitance of a structure, pass only a single <spiral> argument. The effect of a shield or substrate tap can be captured by passing a second <spiral> argument corresponding to the grounding structure.
Notes:
(1) This command performs a full three-dimensional capacitance calculation. The minimum grid size used to calculate the charge distribution is set by the ratio of fftsize parameter in the Technology File and techfile.
(2) The coupling impedance can have a negative real part. This is not a numerical error. You can verify that the impedance looking into any segment has a positive real part regardless of the impedance grounding any other segment.
(3) In the capacitance matrix computation, the thickness of conductors is ignored and conductors are treated as sheets. This restriction will be removed in a future version.
Aliases: coupling,k,coup
Summary: Calculate the magnetostatic coupling occurring between N spirals.
The calculation is performed in free space ignoring any magnetic or conductive properties of the substrate for static fields. The results are only valid at low frequencies. To compute the frequency dependent coupling coefficient use the coupling2 command. For more complete analysis at higher frequencies, use the 2port or the calctrans command to include capacitive effects.Aliases: coupling2,k2,coup2,kf
Summary: Calculate the magnetostatic coupling occurring between Nspirals at a specified frequency.
The calculation is performed in free space ignoring any magnetic or conductive properties of the substrate. To capture skin and proximity effects (eddy currents in the metallization), the spiral segments are subdivided (see cell and autocell) and the inductance matrix order is reduced by invoking current continuity at the device level (current entering every device must exit the device). For more complete analysis (including displacement current) you should use the 2port or the calctrans command.Aliases: inductance,ind,induc,l
Summary: Calculate the DC or the effective AC inductance of a spiral.
The inductance is calculated in free-space neglecting the magnetic and conductive effects of the substrate. The current distribution across the volume of conductors is assumed uniform and the Geometric Mean Distance approximation or Axial Filament approximation is used to calculate the mutual coupling and self-inductance of the structures.If an optional frequency is specified, the effective inductance is calculated using the pi command. The effective inductance includes the capacitive effects and thus beyond self-resonance the inductance will be negative, an indication of capacitive behavior. For a high Q inductor, just before self-resonance, peaking may occur boosting the inductance beyond the DC value. For the most accurate results, use the pix command.
To calculate the real inductance at high frequency including the skin-effect and proximity effects use the lmat command. At high frequencies, the physical inductance decreases asymptotically to the external inductance limit.
Aliases: lmat,indmat,lrmat,zmat
Arguments:
Aliases: pi,pimodel,picircuit,pieq
Summary: Calculate the equivalent Pi circuit of a spiral at a single frequency.
The Pi parameters are equivalent to the 2-port parameters of the spiral at any frequency. See the faq for more details of this.The calculation is performed by calculating an approximate 2-port representation for each segment of the spiral and cascading the 2-ports for each segment. The final 2-port representation is converted into the Pi form. The translation is one-to-one and thus unique. The quality factor Q is also reported with three numbers representing the input, output, and differential quality factors (see q).
There are many approximations in the Pi command and thus this command executes very quickly and forms the backbone of many of the optimization commands. The main assumption is that each segment can be considered as a 2-port and thus all interactions with other segments are lumped into a 2-port model. The substrate loss calculation is also approximate. The inductance computation ignores the substrate and thus magnetic and conductive effects of the substrate are neglected. Finally, the skin-effect is calculated in an approximate manner and proximity-effects of nearby conductors is thus neglected.
Note: The Pi command only works with planar structures which are constructed by series interconnection of segments. Thus multi-metal series and shunt structures should be analyzed with the (pix) command.
Aliases: pi2,pimodel2,picircuit2,pieq2
Note: This command has been replaced by the pix command.Aliases: pi3,pimodel3,picircuit3,pieq3
Note: This command has been replaced by the pix command.Aliases: pi4,pimodel4,picircuit4,pieq4
Arguments:
Aliases: pic,pimodelc,picircuitc,pieqc
This command will treat an interconnection of segments as a capacitor plates.Aliases: piv,pimodelv,picircuitv,pieqv
Summary: Show the high frequency current density in a spiral.
This command shows the results of the pix command graphically by displaying the current density plot in a separate window. See pix for a full explanation of the command line arguments.Aliases: pix,pimodelx,picircuitx,pieqx
This command calculates the 2-port parameters of a spiral structure using electromagnetic analysis. There is no limitation on the structure of the spiral and thus the spiral can be an arbitrary interconnection (shunt or series) of metal segments. There is an quasi-static assumption which limits the highest frequency of analysis but usually this frequency is well beyond the self-resonant frequency of the inductor.The routine works as follows. First, the partial inductance matrix is calculated for the structure by dividing each segment by length, thickness, and width and calculating the self and mutual inductance between every pair of sub-segments. The partitioning of segments is controlled by the various cell size environmental variables (see the autocell and maxl and variables). The partial inductance matrix is reduced in order and lumped into a segment to segment partial inductance matrix. The partial inductance matrix is calculated in free air and thus any magnetic or conductive properties of the substrate are ignored. This is usually a good assumption for substrates on the order of 1 Ohm-cm or more resistive. If eddy is enabled, for highly conductive substrates, eddy currents in the substrate give rise to reflected losses and this is included in the calculation for Manhattan geometries. Reduction in inductance due to ground currents is not included in this calculation.
Next the capacitance matrix is calculated by dividing up segments in width and length only. The thickness of segments is assumed to be small enough so that charge density does not vary significantly over the thickness of the conductor. This assumption is valid form most thin IC metal layers but will result in errors for very thick metal. The partitioning is now controlled by the autocell and/or cmaxl environmental variables. The 3-D capacitance matrix is calculated using the Green function which includes the lossy and coupling effects of the substrate.
The substrate back-plane is assumed to be grounded. This assumption can be removed by employing a non-conductive layer as the first layer in the technology file. This could model epoxy glue or other dielectric materials. Then <spiral gnd> should consists of an interconnection of metals that ground the substrate. For instance, <spiral gnd> might consists of a substrate tap only, a conducting wire touching the substrate. Otherwise <spiral gnd> may consist of a ring of substrate contacts surrounding the inductor. Even metal pads can be included in the calculation. A further application <spiral gnd> is to simulate the electrical effects of a shield. A solid metal layer placed below the spiral can model the shielding effects and the potential gains in Q.
Finally the partial inductance and capacitance matrix are used to solve for the 2-port parameters of the device.
Note: A solid shield is included in the capacitance matrix calculation but it is ignored by the inductance matrix calculation. Thus in reality you must pattern the shield to avoid eddy current effects in the shield. Also, even a patterned shield cannot prevent eddy current effects from occurring in the substrate and thus the Q factor reported by ASITIC might be optimistic if the substrate conductivity is high (below 1 ohm-cm) and eddy is not enabled.
Aliases: q,quality
This command will calculate the Q (Quality Factor) of a spiral at a particular frequency. Three numbers are reported, the first two are single-ended quality factors and the final is a differential quality factor. The first number represents the Q when the "last" terminal is grounded. This is usually the innermost terminal of a spiral unless the order of segments has been altered by the flip command. The second number is the Q with the "first" (usually outer) terminal grounded. Finally, the last number represents the Q when the spiral is driven differentially.The Q is calculated by dividing the imaginary part of the input impedance by the real part. Thus, the Q is zero at self-resonance and the Q is negative beyond the resonance frequency (before the second resonant frequency).
The Q factor is also reported in the pi family of commands. Use pix for the most accurate calculation.
Aliases: resis,res,r,loss
Summary: Calculate the DC or the effective AC resistance of a spiral.
This command calculates the resistance of a spiral by summing over the resistances of all sub-segments that make up the conductor. If a segment has shunt segments, the parallel resistance is computed. This is a DC calculation assuming uniform current distribution across the volume of conductors.If an optional frequency is specified, the effective resistance is calculated with the aid of the pi command. Here the resistance is actually only an effective resistance that may increase or decrease from the DC value. The increase is due to skin and proximity effects whereas the decrease is due to the distributed nature of the substrate current injection. This is explained in more detail in the faq. Thus, R may even go negative.
To calculate the real resistance including only internal impedance effects (skin and proximity effects), use the lmat command. If eddy is turned on, this will include the reflected resistance of the substrate due to eddy current effects. For the most accurate results, use the pix command.
Aliases: resishf,reshf,rhf,rf
This command calculates the series resistance of a spiral at frequency <freq> assuming the spiral is unwound and no magnetic coupling occurs between segments of the spiral. Thus only skin effect is included in the analysis. To see skin and proximity effects and eddy currents in the bulk use the lmat command.Aliases: selfres,sr,srf,imz
This command will find the frequency f where the imaginary part of the input impedance crosses zero. If the user specifies single-ended mode <S>, then the input impedance is defined with one port grounded. In differential mode, <D>, the input impedance is calculated as the voltage difference between the nodes for a unit current injected into the two-port.
The <spiral> argument specifies the device under analysis. The <freq1> and <freq2> specify the frequency range to search. It is important to bracket the search around a single self-resonant frequency since ASITIC only searches for a single frequency. The input impedance is calculated using 2-Port analysis in <fast> mode and using EM analysis in <slow> mode. <slow> mode is recommended as the 2-Port analysis is invalid near the self-resonant frequency. If an optional <spiral gnd> is specified, then EM analysis is performed assuming a grounding structure. <f_step> specifies the frequency resolution to resolve the SRF to. Note that in <slow> mode, data files must be generated at each <f_step> increment. The search terminates in at most <max_iterations> steps.
An estimated SRF is also reported in the Pi family of commands.
Aliases: shuntr,maxr,pr,parallelr
This command will calculate the equivalent shunt input resistance of a spiral. In other words, this routine calculates one over the real part of the input admittance of the spiral.The first argument specifies if the input admittance should be calculated single-endedly or differentially. In single-ended operation one port of the spiral is grounded whereas in differential mode the voltage difference between the two ports is used.
Without any other arguments, the results of the previous analysis is used (such as pi or pix). With optional <spiral> and <freq> arguments, analysis will be performed to determine the input admittance. <fast>, the default behavior, instructs 2-Port analysis to be used (pi) whereas <slow> instructs ASITIC to use EM analysis (pix).
Aliases: zin
This command will calculate the complex input impedance of a spiral.
The first arguments specifies if the input admittance should be calculated single-endedly or differentially. In single-ended operation one port of the spiral is grounded whereas in differential mode the voltage difference between the two ports is used.
Without any other arguments, the results of the previous analysis is used (such as pi or pix). With optional <spiral> and <freq> arguments, analysis will be performed to determine the input admittance. <fast>, the default behavior, instructs 2-Port analysis to be used (like the Pi command) whereas <slow> instructs ASITIC to use EM analysis (pix).