CIRCUIT-ADMITTANCE

NAME
SYNOPSIS
OPTIONS
DESCRIPTION
CAVEATS
EXAMPLE SCRIPT
AUTHOR
SEE ALSO

NAME

circuit ... admittance - Tool to determine the two-port admittance matrix for two nodes of a network.

SYNOPSIS

circuit cell admittance [options] [--] script

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

CAVEATS

The tool can be used for small circuits only. If you need to determine the admittances of larger networks, you may want to use the spice parameter to the show command (as explained above) to generate SPICE input files. The input and output currents i(vin) and i(vout) mentioned in the SPICE files are numerically equivalent to the matrix elements Y11 and Y12, respectively.

Note that non-linear elements such as transistors are implicitly removed from the circuit before determining the admittances.

EXAMPLE SCRIPT

grounded: vss 0 twoport: 5 6 twoport: 1 5 sweep: 1 1e10 10 show: r12 spice