I ran into a problem with ngspice when trying to simulate a circuit which includes a THS4551 from TI.

I obtained the PSpice model for the TI amplifier from the TI website [1].

I am currently using Kicad 5.1.6 with a self compiled version of ngspice-32 on Debian.

In order to make the PSpice model of the TI amplifier work, I set up my `~/.spiceinit`

as follows:

```
* user provided init file
set ngbehavior=ps
```

This made most of the initial errors in my ngspice simulation disappear.

But now I have a problem with a very specific part of the THS4551 PSPice model:

```
.SUBCKT 08_OP_AMP_COMPLETE_W2_THS4551 1 2 3 4
VW_W2 1 2 DC 0V
.MODEL _W2 ISWITCH ROFF=10MEG RON=1 IOFF=5U ION=7U
.ENDS 08_OP_AMP_COMPLETE_W2_THS4551
```

There are two parts which use an `ISWITCH`

model as pasted above. `ISWITCH`

is a purely PSpice model and does not directly exist in ngspice.

I would have assumed, that the PSpice compatibility mode of ngspice would translate this to an equivalent ngspice model, but this does not seem to be the case.

The ngspice-32 manual [2] in section 16.14.3.2 shows, how the related `VSWITCH`

model is translated from PSpice to ngspice:

The VSwitch

`S1 2 3 11 0 SW .MODEL SW VSWITCH(VON=5V VOFF=0V RON=0.1 ROFF=100K)`

may become

`a1 %v(11) %gd(2 3) sw .MODEL SW aswitch(cntl_off=0.0 cntl_on=5.0 r_off=1e5+ r_on=0.1 log=TRUE)`

but for the `ISWITCH`

no such substitution is documented.

I tried to implement a similar substitution for the case of the `ISWITCH`

model, as follows:

```
.SUBCKT 08_OP_AMP_COMPLETE_W2_THS4551 1 2 3 4
a_W2 %id(1 2) %gd(3 4) _W2
.MODEL _W2 aswitch(r_off=10MEG r_on=1 cntl_off=5U cntl_on=7U)
.ENDS 08_OP_AMP_COMPLETE_W2_THS4551
```

by making use of a `aswitch`

ngspice model. But I am not sure if this is correct, and my circuit does not seem to simulate properly.

Does anybody have any experience, in how to model a `ISWITCH`

PSpice mode in ngspice?

[1] https://www.ti.com/lit/tsm/sboma28

[2] http://ngspice.sourceforge.net/docs/ngspice-manual.pdf

Ps: This is a pure ngspice issue, so if somebody knows a good ngspice forum where to post this question, please let me know