ngspice/README.SEEgenerator

SEE (single event effects) generator

The SEE generator generates current pulses, which resemble the 
charge generation and flow causes by a penetrating particle.

How to use it:
Select LET and charge collection depth cdepth, define them as parameters.
Identify all nodes of a circuit netlist which are pn junctions,
and thus are sensitive to pulses.

Set up the SEEgenerator by adding for example

* charge collection depth (in µm)
.param d = 1
* LET (linear energy transfer) in MeV*cm²/mg
.param let = 12
aseegen1 NULL [%id(xcell.n1 m1) %id(xcell.n2 m2) %id(xcell.n1 m1) %id(xcell.n2 m2)] seemod1
.model seemod1 seegen (tdelay = 11n tperiod=25n let='let' cdepth='d')

to the netlist. 

Each sensitive node from the (flattend) netlist may be added to assegen1, together with its 
reference node, for example GND for NMOS, nwell potential for PMOS. This procedure is
currently to be done manually, an automated setup is in preparation.

After a transient simulation, plotting the data output versus a non-radiated device
may reveal the SEE influence.

Several examples are gieven in ./src/axamples/xspice/see: inverters, SRAM cell, opamp,
also as loop with varying LET to detect the threshold. 

As literature please see for example
    Ygor Quadros de Aguiar, Frédéric Wrobel. Jean-Luc Autran, Rubén García Alía
    Single-Event Effects, from Space to Accelerator Environments
    Springer 2025

Detailed description (will be added to the manual):

NAME_TABLE:

C_Function_Name:       cm_seegen
Spice_Model_Name:      seegen
Description:           "single event effect generator"


PORT_TABLE:

Port_Name:             ctrl                 out
Description:          "control input"       "output"
Direction:             in                   out
Default_Type:          v                    i
Allowed_Types:         [v,vd,i,id]          [i,id]
Vector:                no                   yes
Vector_Bounds:         -                    [1 -]
Null_Allowed:          yes                  no


PARAMETER_TABLE:

Parameter_Name:     tfall                    trise
Description:        "pulse fall time"        "pulse rise time"
Data_Type:          real                     real
Default_Value:      500e-12                  20e-12
Limits:             -                        -
Vector:              no                      no
Vector_Bounds:       -                       -
Null_Allowed:       yes                      yes


PARAMETER_TABLE:

Parameter_Name:     tdelay                 inull
Description:        "pulse delay"          "max current"
Data_Type:          real                   real
Default_Value:      0                      0
Limits:             -                      -
Vector:              no                    no
Vector_Bounds:       -                      -
Null_Allowed:       yes                    yes


PARAMETER_TABLE:

Parameter_Name:     tperiod                ctrlthres
Description:        "pulse repetition"     "control voltage threshold"
Data_Type:          real                   real
Default_Value:      0                      0.5
Limits:             -                      -
Vector:              no                    no
Vector_Bounds:      -                      -
Null_Allowed:       yes                    yes


PARAMETER_TABLE:

Parameter_Name:     let                    cdepth
Description:        "lin energy transfer"  "charge collection depth"
Data_Type:          real                   real
Default_Value:      10                     1
Limits:             -                      -
Vector:             no                     no
Vector_Bounds:      -                      -
Null_Allowed:       yes                    yes


PARAMETER_TABLE:

Parameter_Name:     angle                  perlim
Description:        "particle angle"       "pulse repetition"
Data_Type:          real                   boolean
Default_Value:      0                      TRUE
Limits:             [0 1.57079]            -
Vector:             no                     no
Vector_Bounds:      -                      -
Null_Allowed:       yes                    yes

STATIC_VAR_TABLE:

Static_Var_Name:    last_t_value
Data_Type:          pointer
Vector:              no
Description:        "next pulse start time"

STATIC_VAR_TABLE:

Static_Var_Name:    pulse_number
Data_Type:          pointer
Vector:              no
Description:        "number of pulse"

STATIC_VAR_TABLE:

Static_Var_Name:    last_ctrl
Data_Type:          pointer
Vector:              no
Description:        "last control value"

Description
This code model generates "double exponentially" formed current pulses according to

i(t) = inull * (exp(-(t-tdelay)/tfall) - (exp(-(t-tdelay)/trise) for t > tdelay
i(t) = 0       for t < tdelay

with inull given as parameter input or (if not given), calculated as
inull = 1.035e-14 * let/cos(angle) * cdepth / (tfall - trise)
with data for silicon, cdepth in µm, let in MeV*cm²/mg, angle in radians.

Minimum is one pulse output (a node pair, or a single node with the other grounded).
Several output node pairs may be defined per code model instance. Parameter tperiod
may then be used to create pulses in sequence. Per default only one sequence is running,
with one pulse for each node.
Parameter perlim, set to FALSE, allows running and repeating the sequence until
the end of the simulation. The first pulse is issued in the first
node pair of the node list in the vector [], the second (after time tperiod has elapsed), 
is injected by the second node (pair) of the list and so on. When the sequence is repeated, 
again the output starts pulsing at port (node pair) number 1.

The control input ctrl (voltage or current) may be used
to start or repeat the whole sequence, depending on the circuit status. A rising voltage
at ctrl, when crossing the threshold given by ctrlthres, will initiate the sequence (including
tdelay and tperiod).

This model will work in transient analysis.

Example ngspice usage (with control)

aseegen1 ctrl [%id(n1 m1) %id(n2 m2) %id(n1 m1) %id(n2 m2)] seemod1
.model seemod1 seegen (tdelay = 8n tperiod=25n)

Example ngspice usage (without control, ctrl replaced by NULL, parameters as offered by default)

aseegen2 NULL [%id(n1 m1) %id(n5 n6) %id(n6 n7) %i(isingle) ] seemod2
.model seemod2 seegen (tdelay = 0 tperiod=0 ctrlthres=0.5 inull=0 tfall=500p trise=20p perlim=FALSE)