In some cases a device is specified by a model and if model parameters can not be set in the + instance line we need multiple models if we want to use multiple devices with different model parameters. + This can be done by specifying a model in the following way:
++type=mechanical_rotational +format="@name @pinlist inertia@name +.model inertia@name inertia_omega_tau J=@J" +template="name=N1 J=1.1" ++
Note the model name is given as inertia@name, this will make each model instance have a + different and unique name. This will generate an instance line:
++N1 A B C inertiaN1 +.model inertiaN1 inertia_omega_tau J=1.4 ++ +
A better way hat handles also vectored instances is the following:
++type=mechanical_rotational +format="@name @pinlist #inertia#@name +.model #inertia#@name inertia_omega_tau J=@J" +template="name=N1 J=1.1" ++
This way if you place a vectored instance name=N1[3:0] it will expand in netlist as:
++N1[3] XAA XBB XCC inertiaN1[3] +N1[2] XAA XX XCC inertiaN1[2] +N1[1] XAA XX XCC inertiaN1[1] +N1[0] XAA XX XCC inertiaN1[0] +.model inertiaN1[3] inertia_omega_tau J=1.2 +.model inertiaN1[2] inertia_omega_tau J=1.2 +.model inertiaN1[1] inertia_omega_tau J=1.2 +.model inertiaN1[0] inertia_omega_tau J=1.2 ++ +
In general SPICE allows parameters to be passed to subcircuits. This is the case for dimensions, like
+ W=2u, L=0.15u that are passed to a subcircuit.
+ The subcircuit uses these parameters (W, L) instead of numbers,
+ making the subcircuit truly parametric. However transistor models in a subcircuit can not be passed as parameters,
+ the following inverter instantiation is illegal:
+
+ X1 A Y inverter W=2u L=0.15u modn=cmosn modp=cmosp
+ To overcome this problem Xschem must generate multiple subcircuits.
+ Consider the following inv3.sym symbol:
+ the symbol has the following attributes:
++type=subcircuit +format="@name @pinlist @VCCPIN @VSSPIN @symname wn=@wn lln=@lln wp=@wp lp=@lp m=@m" +template="name=x1 m=1 modn=xmodn modp=xmodp ++ wn=10u lln=1.2u wp=10u lp=1.2u ++ VCCPIN=VCC VSSPIN=VSS" +extra="VCCPIN VSSPIN modn modp" ++
In above attributes two parameters are defined that specify transistor models, modn and + modp, with default values (if unspecified in instance) xmodn and xmodp. + The inverter subcircuit transistors will use the @modn and @modp as SPICE models:
+
+ If an inv3.sym is placed n the schematic and no schematic=... parameter is given + to create an instance based subcircuit specialization:
+The following netlist will be produced:
++x2 LDCP3_B LDCP vcc vss inv3 wn=8.4u lln=2.4u wp=20u lp=2.4u m=1 +... +... +.subckt inv3 y a VCCPIN VSSPIN wn=10u lln=1.2u wp=10u lp=1.2u +*.opin y +*.ipin a +m2 y a VCCPIN VCCPIN xmodp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1 +m1 y a VSSPIN VSSPIN xmodn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1 +.ends ++
However if another instance is placed:
+
+ with following attributes:
++name=x3 m=1 ++ wn=8.4u lln=2.4u wp=20u lp=2.4u ++ VCCPIN=vcc VSSPIN=vss +schematic=@symname\_1.sch +modn=yyn modp=yyp ++
the following netlist is generated:
++x3 LDCP_B LDCP vcc vss inv3_1 wn=8.4u lln=2.4u wp=20u lp=2.4u m=1 +... +... +.subckt inv3_1 y a VCCPIN VSSPIN wn=10u lln=1.2u wp=10u lp=1.2u +*.opin y +*.ipin a +m2 y a VCCPIN VCCPIN yyp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1 +m1 y a VSSPIN VSSPIN yyn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1 +.ends ++
You see that a second inv_1.sym is generated with changed models (yyn and yyp). + This allows you to reuse the same symbol with different model names. Xschem does the necessary work to + duplicate the subcircuit, since model names can not be set as parameters. +
+ +