paramset_examples

paramset_examples — Verilog-AMS paramset blocks (Enhancement-21)

Demonstrates paramset blocks, using version11's own openvaf-r and ngspice-46. A paramset defines a named, instantiable model that specialises an existing behavioural module by binding some of its parameters — the Verilog-AMS way of shipping a model library (one module, several named pre-configured variants), analogous to a set of SPICE .model cards but written in Verilog-AMS and able to compute the bound values.

Syntax

paramset <name> <target_module>;
    parameter real <p> = <default>;   // the paramset's own (card) parameters
    .<target_param> = <expr>;         // bind a target-module parameter
endparamset

<name> becomes its own OSDI model (usable as .model foo <name> in a netlist). It has the same terminals and analog behaviour as <target_module>, but each bound target parameter takes the value of its <expr> (which may reference the paramset's own parameters) and is no longer settable from the model card. Target parameters that are not bound remain settable (pass-through).

What paramset_demo.va shows

One behavioural module conductor = g0*(1 + k*V) (a mildly nonlinear conductance) and three paramsets:

• res_1k — a fixed 1 kΩ resistor (both parameters bound to constants);
• res_kohm — resistance set in kΩ through a card parameter kohm, with the conductance computed as 1/(kohm*1000);
• varistor — binds only k (from card parameter kv) and leaves g0 settable (pass-through).

Run

python3 verify_paramset.py

Expected:

res_1k        I(1V)  = V/1kOhm    ... PASS
res_kohm(k=2) I(1V)  = V/2kOhm    ... PASS
res_kohm(.5)  I(1V)  = V/500      ... PASS
varistor      I(0.4) nonlinear    ... PASS
varistor      bound k not settable... PASS
varistor      AC gm = g0(1+2kV)   ... PASS
conductor     base module intact  ... PASS
ALL PASS

The checks prove that constant bindings, card-parameter-driven binding expressions, and pass-through of unbound parameters all work; that a bound parameter is not settable from the card (setting k=9 is ignored); that the derivative flows through the paramset (the AC conductance gm = g0(1+2kV) is exact — the autodiff Jacobian runs on the shared body under the paramset); and that the base module conductor still works independently.

Notes / limitations

• The target module must be declared in the same file.
• Bound parameters become internal localparams of the specialised model.
• Not supported (future work): multiple paramsets sharing one name with instance-based selection, and aliasparam/statement-based selection blocks — each paramset here maps to exactly one model.