f



spectre captab?

Spectre has the option to print all the node capacitance values with
an option called captab in the DC analysis options form.  I specified
node to node capacitance.  The circuit consists of 1 diode connected
npn.  In my spectre.out file I see the following:

Q1:int_b : 0                variable=0            0           
Q1:int_b : Q1:int_b         variable=536.081f    536.081f 
Q1:int_b : Q1:int_c         variable=201.324f    201.324f 
Q1:int_b : Q1:int_e         variable=334.757f    334.757f 
Q1:int_b : net24            variable=0            -0        
Q1:int_c : 0                variable=98.8871f    98.8871f   
Q1:int_c : Q1:int_b         variable=201.559f    201.559f 
Q1:int_c : Q1:int_c         variable=300.446f    300.446f 
Q1:int_c : Q1:int_e         variable=0            -0        
Q1:int_c : net24            variable=0            -0        
Q1:int_e : 0                variable=0            0           
Q1:int_e : Q1:int_b         variable=334.522f    334.522f 
Q1:int_e : Q1:int_c         variable=234.671a    234.671a 
Q1:int_e : Q1:int_e         variable=334.757f    334.757f 

Questions:
1.  Why is the b-c and c-b capacitance slightly different?
2.  What is the meaning of the b-b, c-c, and e-e capacitance?
3.  It is diode connected so why do I have a b-c capacitance?
4.  Can I use the b-c and b-e cap values as Cmu and Cpi in the
hybrid-pi SS model?
5.  Is there a way that I can output the captab results to a separate
file other than spectre.out for postprocessing?
---
Erik
0
erikwanta1 (327)
2/1/2004 7:10:16 PM
comp.cad.cadence 5429 articles. 9 followers. Post Follow

3 Replies
2521 Views

Similar Articles

[PageSpeed] 36

Erik,

Don't have time to check out the other questions,  but spectre itself can
output the captab to an arbitrary file. Add an include file (or a model file)
with:

mycaptab info what=captab where=file ...

Andrew.

On 1 Feb 2004 11:10:16 -0800, erikwanta@starband.net (Erik Wanta) wrote:

>Spectre has the option to print all the node capacitance values with
>an option called captab in the DC analysis options form.  I specified
>node to node capacitance.  The circuit consists of 1 diode connected
>npn.  In my spectre.out file I see the following:
>
>Q1:int_b : 0                variable=0            0           
>Q1:int_b : Q1:int_b         variable=536.081f    536.081f 
>Q1:int_b : Q1:int_c         variable=201.324f    201.324f 
>Q1:int_b : Q1:int_e         variable=334.757f    334.757f 
>Q1:int_b : net24            variable=0            -0        
>Q1:int_c : 0                variable=98.8871f    98.8871f   
>Q1:int_c : Q1:int_b         variable=201.559f    201.559f 
>Q1:int_c : Q1:int_c         variable=300.446f    300.446f 
>Q1:int_c : Q1:int_e         variable=0            -0        
>Q1:int_c : net24            variable=0            -0        
>Q1:int_e : 0                variable=0            0           
>Q1:int_e : Q1:int_b         variable=334.522f    334.522f 
>Q1:int_e : Q1:int_c         variable=234.671a    234.671a 
>Q1:int_e : Q1:int_e         variable=334.757f    334.757f 
>
>Questions:
>1.  Why is the b-c and c-b capacitance slightly different?
>2.  What is the meaning of the b-b, c-c, and e-e capacitance?
>3.  It is diode connected so why do I have a b-c capacitance?
>4.  Can I use the b-c and b-e cap values as Cmu and Cpi in the
>hybrid-pi SS model?
>5.  Is there a way that I can output the captab results to a separate
>file other than spectre.out for postprocessing?
>---
>Erik

--
Andrew Beckett
Senior Technical Leader
Custom IC Solutions
Cadence Design Systems Ltd
0
andrewb3686 (473)
2/2/2004 8:52:15 AM
Hi Erik,

Your question 1 is tricky.

I believe the user manual answers questions 2

(formulas are a bit messed up, here, you can better look at the pdf.)
_______________________________________________________________________<rtfm>
Printing the Node Capacitance Table

The Spectre simulator allows you to print node capacitance to an output 
file. This can help
you in identifying possible causes of circuit performance problems due 
to capacitive loading.

The capacitance between nodes x and y is defined as


July 2002                                     194 
          Product Version 5.0


                                            Spectre Circuit Simulator 
User Guide
                                                         Control Statements




                               q
                           x
C          = �
      xy                  --------
                               vy


where q is the sum of all charges in the terminal connected to node 
                              is the voltage
                         x 
                  x, and vy
at node y.

The total capacitance at node x is defined as


                    q
                  x
C          =
      xx            v
                 --------x


where charge q  and voltage                           are at the same node
                                       x        vx 
        x.

You may use the captab analysis to display the capacitance between the 
nodes in your
circuit. This is an option in the info statement. Here is an example of 
the info settings you
would set to perform a captab analysis:


Parameter Setting                              Action Taken

what=captab                                    Performs captab analysis. 
The default value is
                                                oppoint.

where=logfile                                  Prints the parameters to 
a logfile. Other possible values
                                                are nowhere, screen, and 
file. The value rawfile is
                                                not supported for node 
capacitance.

title=captab                                   Prints captab as the 
title of the analysis in the output
                                                file.

threshold=0                                    Specifies the threshold 
capacitance value. The nodes for
                                                which the total node 
capacitance is below the threshold
                                                value will not be 
printed in the output table.

detail=node                                    Displays the total node 
capacitances. Other possible
                                                values are nodetoground 
and nodetonode.

sort=value                                     Sorts the captab output 
according to value. The other
                                                possible value is name.


For a complete list of captab parameters and values, consult the Spectre 
online help
(spectre -h).


July 2002                                                       195 
                          Product Version 5.0


                          Spectre Circuit Simulator User Guide
                                       Control Statements



You may use the infotimes option of the transient analysis when you bind 
the captab
analysis to a transient analysis. This runs the captab analysis at 
specified time intervals. The
syntax for the infotimes option is

infotimes=[x1, x2...]

where x1 and x2 are time points for which the info analysis should be 
performed. The
following is an example of binding a captab analysis to a transient 
analysis.

tran1         tran     stop=1 �    infotimes=[0.1 �  0.5 � ]infoname=capInfo
capInfo       info     what=captab       where=file         file='capNodes'
detail=nodetonode



Output Table

The output for the captab analysis is printed in the following format:

n     The first column displays the names of the two nodes 
(From_node:To_Node).

n     The second column displays the fixed (linear) capacitance between 
the two nodes.

n     The third column is the variable (non-linear) capacitance between 
the two nodes.

n     The last column displays the total capacitance between the nodes.

Table 7-1 displays the output for the circuit below when detail=nodetonode:



               C3=1p


                                                        0.5p
                                               n1 
     n3

                         C2=2p
        n2 
      1p


                                                1p


      C1=2p





July 2002                                     196 
           Product Version 5.0


                           Spectre Circuit Simulator User Guide
                                        Control Statements



In this circuit, the total capacitance at node 2 (n2:n2 in the table) is:
C1+C2+C3=5p

The total capacitance between node 2 and node 1 (n2:n1) is:
C2(Linear)+C3(Non-Linear)=3p

Table 7-1 Node Capacitance Table Sorted by Value



n2:n2            Fixed=2p                Variable=3p 
Sum=5p

n2:n1            Fixed=2p                Variable=1p 
Sum=3p



n1:n1            Fixed=3.5p              Variable=1p 
Sum=4.5p

n1:0             Fixed=1p                Variable=0 
Sum=1p

n1:n2            Fixed=2p                Variable=1p 
Sum=3p

n1:n3            Fixed=0.5p              Variable=0 
Sum=0.5p

n3:n3            Fixed=1.5p              Variable=0 
Sum=1.5p

n3:0             Fixed=1p                Variable=0 
Sum=1p

n3:n1            Fixed=0.5p              Variable=0 
Sum=0.5p



The total node capacitance at nodes 1, 2, and 3 is represented by the 
rows n1:n1, n2:n2,
and n3:n3 respectively.

There is no entry for n3:n2, which means there is no capacitance between 
these two nodes.

Table 7-1 is sorted by value. The rows are first grouped according to 
node names - the rows
with the same From_Node are kept in a group. The row depicting the total 
capacitance at
each node is always displayed first in the group, and the row displaying 
the node-to-ground
capacitance is second. The remaining rows within each group are sorted 
in descending order
of the Sum value.

Note: If the threshold is set to 2p (thresh=2p), the row n1:n3 will not 
be printed since the
capacitance between them is less than the threshold. The row n1:0 will 
be printed since the
node-to-ground capacitance is always printed. The group n3:n3, n3:0, and 
n3:n1 will not
be printed because the total node capacitance at node 3 (n3:n3) is less 
than the threshold.

If you sort the table by name (sort=name), it would look as follows:




July 2002                                       197 
            Product Version 5.0


                         Spectre Circuit Simulator User Guide
                                      Control Statements



Table 7-2  Node Capacitance Table Sorted by Name


n1:n1              Fixed=3.5p               Variable=1p 
Sum=4.5p

n1:0               Fixed=1p                 Variable=0                Sum=1p

n1:n2              Fixed=2p                 Variable=1p               Sum=3p

n1:n3              Fixed=0.5p               Variable=0 
Sum=0.5p



n2:n2              Fixed=2p                 Variable=3p               Sum=5p

n2:0               Fixed=0                  Variable=2p               Sum=2p

n2:n1              Fixed=2p                 Variable=1p               Sum=3p



n3:n3              Fixed=1.5p               Variable=0 
Sum=1.5p

n3:n0              Fixed=1p                 Variable=0                Sum=1p

n3:n1              Fixed=0.5p               Variable=0 
Sum=0.5p



In this case, the From_Node:To_Node column is sorted alpha-numerically. 
However, the
row depicting the total capacitance at each node is always displayed 
first in the group, and
the row displaying the node-to-ground capacitance is second.
______________________________________________________________________</rtfm>



For question 3: a shorted capacitor is still a capacitor. If you ask for 
all the operating point capacitors of a bipolar, you will get them all, 
no matter what the network around this bipolar is.

Question 4: It seem Cmu is between intrinsic base and intrinsic 
collector, what you print also. That should be OK.

(question 5 : answered by Andrew, and documented by "spectre -h info")


When you get an answer about Q1, please post it.

-- 
Frederic

Erik Wanta wrote:
> Spectre has the option to print all the node capacitance values wit
> an option called captab in the DC analysis options form.  I specified
> node to node capacitance.  The circuit consists of 1 diode connected
> npn.  In my spectre.out file I see the following:
> 
> Q1:int_b : 0                variable=0            0           
> Q1:int_b : Q1:int_b         variable=536.081f    536.081f 
> Q1:int_b : Q1:int_c         variable=201.324f    201.324f 
> Q1:int_b : Q1:int_e         variable=334.757f    334.757f 
> Q1:int_b : net24            variable=0            -0        
> Q1:int_c : 0                variable=98.8871f    98.8871f   
> Q1:int_c : Q1:int_b         variable=201.559f    201.559f 
> Q1:int_c : Q1:int_c         variable=300.446f    300.446f 
> Q1:int_c : Q1:int_e         variable=0            -0        
> Q1:int_c : net24            variable=0            -0        
> Q1:int_e : 0                variable=0            0           
> Q1:int_e : Q1:int_b         variable=334.522f    334.522f 
> Q1:int_e : Q1:int_c         variable=234.671a    234.671a 
> Q1:int_e : Q1:int_e         variable=334.757f    334.757f 
> 
> Questions:
> 1.  Why is the b-c and c-b capacitance slightly different?
> 2.  What is the meaning of the b-b, c-c, and e-e capacitance?
> 3.  It is diode connected so why do I have a b-c capacitance?
> 4.  Can I use the b-c and b-e cap values as Cmu and Cpi in the
> hybrid-pi SS model?
> 5.  Is there a way that I can output the captab results to a separate
> file other than spectre.out for postprocessing?
> ---
> Erik

0
cad_support (285)
2/2/2004 4:41:58 PM
FYI

I opened SR 32715538 to allow me to specify a captab output file in
the captab section of the DC options form.
---
Erik


Andrew Beckett <andrewb@DELETETHISBITcadence.com> wrote in message news:<um3s109l5acvog5k4cfv9449s28m023f1d@4ax.com>...
> Erik,
> 
> Don't have time to check out the other questions,  but spectre itself can
> output the captab to an arbitrary file. Add an include file (or a model file)
> with:
> 
> mycaptab info what=captab where=file ...
> 
> Andrew.
> 
> On 1 Feb 2004 11:10:16 -0800, erikwanta@starband.net (Erik Wanta) wrote:
> 
> >Spectre has the option to print all the node capacitance values with
> >an option called captab in the DC analysis options form.  I specified
> >node to node capacitance.  The circuit consists of 1 diode connected
> >npn.  In my spectre.out file I see the following:
> >
> >Q1:int_b : 0                variable=0            0           
> >Q1:int_b : Q1:int_b         variable=536.081f    536.081f 
> >Q1:int_b : Q1:int_c         variable=201.324f    201.324f 
> >Q1:int_b : Q1:int_e         variable=334.757f    334.757f 
> >Q1:int_b : net24            variable=0            -0        
> >Q1:int_c : 0                variable=98.8871f    98.8871f   
> >Q1:int_c : Q1:int_b         variable=201.559f    201.559f 
> >Q1:int_c : Q1:int_c         variable=300.446f    300.446f 
> >Q1:int_c : Q1:int_e         variable=0            -0        
> >Q1:int_c : net24            variable=0            -0        
> >Q1:int_e : 0                variable=0            0           
> >Q1:int_e : Q1:int_b         variable=334.522f    334.522f 
> >Q1:int_e : Q1:int_c         variable=234.671a    234.671a 
> >Q1:int_e : Q1:int_e         variable=334.757f    334.757f 
> >
> >Questions:
> >1.  Why is the b-c and c-b capacitance slightly different?
> >2.  What is the meaning of the b-b, c-c, and e-e capacitance?
> >3.  It is diode connected so why do I have a b-c capacitance?
> >4.  Can I use the b-c and b-e cap values as Cmu and Cpi in the
> >hybrid-pi SS model?
> >5.  Is there a way that I can output the captab results to a separate
> >file other than spectre.out for postprocessing?
> >---
> >Erik
0
erikwanta1 (327)
2/3/2004 3:19:48 AM
Reply: