PSPICE Error

[Cujo]

I'm trying to do a transient analysis with respect to the BJT'S Collector-Emitter voltage marker.

But I'm getting an "Node $N_0004 is floating" error with the C1 capacitor. Not sure why I'm getting this error and how to fix it?
 

Here is the error details:



* From [PSPICE NETLIST] section of pspiceev.ini:
.lib "nom.lib"

.INC "Schematic2.net"

**** INCLUDING Schematic2.net ****
* Schematics Netlist *



C_C2         0 $N_0001  10u 
Q_Q1         $N_0003 $N_0002 $N_0001 Qbreakn
C_C1         $N_0004 $N_0002  10u 
R_R1         $N_0002 $N_0005  80k 
R_RC         $N_0003 $N_0005  4k 
R_RE         0 $N_0001  3.3K 
R_R2         0 $N_0002  40K 
I_Vi         $N_0004 0 
+SIN 0V 10mV 1KHz 0 0 0
V_VCC         $N_0005 0 DC 12V 

**** RESUMING Schematic2.cir ****
.INC "Schematic2.als"



**** INCLUDING Schematic2.als ****
* Schematics Aliases *

.ALIASES
C_C2            C2(1=0 2=$N_0001 )
Q_Q1            Q1(c=$N_0003 b=$N_0002 e=$N_0001 )
C_C1            C1(1=$N_0004 2=$N_0002 )
R_R1            R1(1=$N_0002 2=$N_0005 )
R_RC            RC(1=$N_0003 2=$N_0005 )
R_RE            RE(1=0 2=$N_0001 )
R_R2            R2(1=0 2=$N_0002 )
I_Vi            Vi(+=$N_0004 -=0 )
V_VCC           VCC(+=$N_0005 -=0 )
.ENDALIASES


**** RESUMING Schematic2.cir ****
.probe


.END

ERROR -- Node $N_0004 is floating

[T3sl4co1l]

Why is Vi drawn as a voltage source but modeled as a current source?

A current source does not define a voltage, nor does a capacitor at DC.  Also, a zero current is identical to an open circuit.  So, the message is exactly as it says; the node is floating.

The implication for simulation is, the solver cannot find a solution for that node; it can be literally anything.  The technical term is "singular matrix", which most other SPICEs call it in the error message.  The solution is to add a shunt (from node to GND) resistance or inductance to define that voltage.  Setting RSHUNT to a modest value (say 1e9) may also do the job, but mind it tends to mask the problem and transient simulation can go slowly due to the resulting poorly conditioned (near-singular) matrix.

Tim