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The admittance sub-command of the circuit
tool allows the user to determine the two-port admittance
matrix for two given nodes of a network. This matrix,
traditionally called Y, gives the currents into each node,
given the voltages at each node:
I = Y*V
The matrix elements of Y correspond to admittances in an
equivalent pi-network, as shown below:
Y12
1 ------- 2
V1 ---+----| |----+--- V2
| ------- |
- -
| | | |
| | Y11-Y12 | | Y22-Y12
| | | |
- -
| |
| |
ground
Note that the matrix element Y12 equals the element Y21,
i.e., the matrix Y is symmetrical.
STEP 1
Before invoking the tool, a script file needs to be prepared
with the following format:
grounded: node1 ... nodeN
grounded: node1 ... nodeN
...
twoport: node1 node2
twoport: node1 node2
...
Each line starts with a keyword, followed by a colon,
followed by one or more parameters. A comment line should
start with a hash mark (#). We will now describe the
keywords; an example script is given at the end of this
manual page.
grounded: node1 ... nodeN
This line is used to specify which nodes should be
regarded as "ground" during the measurement of the
admittances. In any case, nodes named 0, GND,
or gnd are taken to be grounded, and therefore it
might not be necessary to specify this parameter. Multiple
lines starting with grounded may be specified.
twoport: node1 node2
This line is used to indicate that the measurement should
be conducted between nodes node1 and node2.
Multiple lines starting with twoport may be specified
to perform multiple measurements.
frequencies: freq1 ... freqN
In case there are capacitive (or inductive) elements
present in the network, the admittances become
frequency-dependent. This line allows you to specify the
frequencies at which measurement takes place. By default,
measurement is done at zero frequency, meaning that
capacitors are ignored, and inductors are
short-circuited.
sweep: begin-freq end-freq num-steps
This line allows you to specify frequencies in an
alternative manner. The parameter begin-freq
specifies the begin frequency, end-freq specifies the
end frequency, and num-steps specifies the number of
steps. The steps are performed exponentially, which implies
that both given frequencies should not be zero.
show: directive1 ... directiveN
This line specifies what output is to be generated.
Possible directives are: y11, y12, y21,
y22 (to show the corresponding Y matrix elements);
r11, r12, r21, r22 (to show
resistances instead of admittances). Furthermore, the
directive spice can be used to also generate a SPICE
network suitable for simulation. The directive y10
may be used as a shortcut for the value of Y11-Y12 (the
admittance to ground from node1). Similarly,
r10 may be used to generate the corresponding
resistance. Also, y20 and r20 may be specified
for the admittance and resistance to ground at
node2.
STEP 2
Before running the script, make sure that the current
directory is a project directory. Also make sure that the
nodes mentioned in the script are present in the circuit.
This can be checked by typing xsls cell.
The script can be run by typing the following command at
the Unix prompt:
# circuit cell admittance script
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