Experimental code, not yet made publicly available.

General form:

.pss gfreq tstab oscnob psspoints harms sciter steadycoeff <uic>

Examples:

.pss 150 200e-3 2 1024 11 50 5e-3 uic
.pss 624e6 1u v_plus 1024 10 150 5e-3 uic
.pss 624e6 500n bout 1024 10 100 5e-3 uic

gfreq is guessed frequency of fundamental suggested by user. When performing transient analysis the PSS algorithm tries to infer a new rough guess rgfreq on the fundamental. If gfreq is out of (\pm)10% with respect to rgfreq then gfreq is discarded.

tstab is stabilization time before the shooting begin to search for the PSS. It has to be noticed that this parameter heavily influence the possibility to reach the PSS. Thus is a good practice to ensure a circuit to have a right tstab, e.g. performing a separate TRAN analysis before to run PSS analysis.

oscnob is the node or branch where the oscillation dynamic is expected. PSS analysis will give a brief report of harmonic content at this node or branch.

psspoints is number of step in evaluating predicted period after convergence is reached. It is useful only in Time Domain plots. However this number should be higher than 2 times the requested harms. Otherwise the PSS analysis will properly adjust it.

harms number of harmonics to be calculated as requested by the user.

sciter number of allowed shooting cycle iterations. Default is 50.

steady_coeff is the weighting coefficient for calculating the Global Convergence Error (GCE), which is the reference value in order to infer is convergence is reached. The lower steady_coeff is set, the higher the accuracy of predicted frequency can be reached but at longer analysis time and sciter number. Default is 1e-3.

uic (use initial conditions) is an optional keyword that indicates that the user does not want ngspice to solve for the quiescent operating point before beginning the transient analysis. If this keyword is specified, ngspice uses the values specified using IC=... on the various elements as the initial transient condition and proceeds with the analysis. If the .ic control line has been specified, then the node voltages on the .ic line are used to compute the initial conditions for the devices. Look at the description on the .ic control line for its interpretation when uic is not specified.