User`s guide
15
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12 Mixed Analo
g
/Di
g
ital Simulation
Interface Generation
and Node Names
The majority of the interface generation process involves
PSpice A/D determining whether analog and digital primitives
are connected, and if so, inserting an interface subcircuit for
each digital connection. This turns the interface node into a
purely analog node, which now connects to the analog terminal
of the interface subcircuit. To complete the original connection,
PSpice A/D creates a new digital node between the digital
terminal of the interface subcircuit and the digital primitive.
Because PSpice A/D must create new digital nodes, it must give
them unique names. These node names are used in Probe output
variables appearing in the list of viewable traces when you select
Trace from the Add menu. Name creation follows these rules:
• The analog node retains the name of the original interface
node—either the labeled wire name in the schematic, or the
node name automatically generated for an unlabeled wire.
• Each new digital node name consists of the labeled wire
name in the schematic or the node name automatically
generated for an unlabeled wire, suffixed with $AtoD or
$DtoA. If the node is attached to more than one digital
device, the second digital node is appended with $AtoD2 or
$DtoA2, and so on.
Figure 15-1 shows a fragment of a mixed analog/digital circuit
before and after the interface subcircuits have been added. The
wires labeled 1 and 2 in the schematic representation are the
interface nets connecting analog and digital devices. These
translate to interface nodes which are processed by PSpice A/D
to effectively create the circuit fragment shown in the PSpice A/
D representation.
After interface generation, node 1 is a purely analog node,
connecting the resistor, transistor, and the analog inputs of both
AtoD subcircuits. Node 2 is also a purely analog node,
connecting the resistor and the analog output of the DtoA
interface. You can see that PSpice A/D inserted two new digital
nodes, 1$AtoD and 1$AtoD2, which connect the outputs of the
AtoD interfaces to the inverter inputs. It also created one digital