ANALYSES
========

This file lists the analyses currently implemented into ngspice.

Table of Contents

 1 Noise analysis (NOISE)
   1.1 Small signal noise
   1.2 Transient noise
 2 Operating point analysis (OP)
 3 Operating point sweep Analysis (DC)
 4 Pole-zero analysis (PZ)
 5 Small-Signal distortion analysis (DISTO)
 6 Small Signal frequency response analysis (AC)
 7 Sensitivity analysis (SENS)
 8 Transfer function analysis (TF)
 9 Transient analysis (TRAN)
 10 Periodic steady state analysis (PSS, experimental feature)
 11 S-parameter analysis (SP)



1 Noise analysis (NOISE)

 1.1 Small signal noise

    The noise analysis does analysis device-generated noise for the given
 circuit. When provided with an input source and an output port, the analysis
 calculates the noise contributions of each device (and each noise generator
 within the device) to the output port voltage. It also calculates the input
 noise to the circuit, equivalent to the output noise referred to the
 specified input source. This is done for every frequency point in a specified
 range - the calculated value of the noise corresponds to the spectral density
 of the circuit variable viewed as a stationary gaussian stochastic process.

 1.2 Transient noise

    Time domain noise analysis during transient simulation is enabled by
 providing voltage (and current) source options with white, 1/f and
 random telegraph signal noise signals.


2 Operating point analysis (OP)

    The operating point analysis determines the dc operating point of the
 circuit with inductors shorted and capacitors opened. If a simple matrix
 solution fails, two versions of gmin stepping may be followed by source
 stepping and finally an OP search by a transient simulation.


3 Operating point sweep Analysis (DC)

    The operating point sweep analysis determines the values of output
 variables while one or two specified independent voltage or current source is
 stepped over a user-specified range and the dc output variables are stored
 for each sequential source value. Resistance and temperature sweep are
 included.


4 Pole-zero analysis (PZ)

    The pole-zero analysis computes the poles and/or zeros in the small-signal
 ac transfer function. The program first computes the dc operating point and
 then determines the linearized, small-signal models for all the nonlinear
 devices in the circuit. This circuit is then used to find the poles and zeros
 of the transfer function. Unfortunately this code is (since its inception in
 spice3) not free of bugs.


5 Small-Signal distortion analysis (DISTO)

    The distortion analysis computes steady-state harmonic and intermodulation
 products for small input signal magnitudes. Not all devices are supported.


6 Small Signal frequency response analysis (AC)

    The ac small-signal computes the ac output variables as a function of
 frequency. The program first computes the dc operating point of the circuit
 and determines linearized, small-signal models for all of the nonlinear
 devices in the circuit. The resultant linear circuit is then analyzed over a
 user-specified range of frequencies.


7 Sensitivity analysis (SENS)

    Ngspice will calculate either the DC operating-point sensitivity or the AC
 small-signal sensitivity of an output variable with respect to all circuit
 variables, including model parameters. Spice calculates the difference in an
 output variable (either a node voltage or a branch current) by perturbing
 each parameter of each device independently.


8 Transfer function analysis (TF)

    The (small signal) transfer function analysis computes the dc small-signal
 value of a transfer function (ratio of output variable to input source),
 input resistance, and output resistance is also computed as a part of the dc
 solution.


9 Transient analysis (TRAN)

    The transient analysis computes the transient output variables as a
 function of time over a user-specified time interval. The initial conditions
 are automatically determined by a dc analysis. All sources which are not time
 dependent (for example, power supplies) are set to their dc value.


10 Periodic steady state analysis (PSS)

    The periodic steady state analysis computes solutions for oscillating
 circuits. Currently only the autonomous case is implemented.


11 S-parameter analysis

    Evaluate S parameters on any port of a multiport circuit, store the resulting
 data in a Touchstone file
    Load S parameters from s2p file into code model, and do ac simulation on an
 automatically generated lumped element circuit.


