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[Gnucap-devel] JFET and initial conditions
From: |
Xavier Romeuf |
Subject: |
[Gnucap-devel] JFET and initial conditions |
Date: |
Fri, 15 Jun 2007 16:15:18 +0200 |
User-agent: |
Thunderbird 2.0.0.4 (X11/20070604) |
Hi,
While developing the Python wrapper for Gnucap, I have encountered an
issue with the JFET ngspice model.
Here is a netlist containing a JFET component based on the ngspice model:
-------------------circuit.ckt--------------------------
*** NJF Test ***
.attach jfet.so
.model J2N3819 NJF(Beta=1.304m Rd=1 Rs=1 Lambda=2.25m Vto=-3 Is=33.57f
+ Cgd=1.6p Pb=1 Fc=.5 Cgs=2.414p Kf=9.882E-18 Af=1)
R3 N528817 N528869 4k
I1 N528855 0 DC 6.1m
R4 N530614 N528973 50
R2 N528849 N528869 4k
V2 N530614 0 SIN 0 1 1e9 0 0
J2 N528817 N529031 N528855 J2N3819
R5 0 N529031 50
J1 N528849 N528973 N528855 J2N3819
V1 N528869 0 18
.END
--------------------------------------------------------
Doing a transient analysis on the node N528849 gives the following
results, which are similar to those given by Spice:
Gnucap> get circuit.ckt
Gnucap> print tran v(N528849)
Gnucap> tran 0 1n 0.1n
#Time v(N528849)
0. 5.8
100.p 6.1586
200.p 6.3693
300.p 6.2136
400.p 5.7429
500.p 5.1405
600.p 4.6337
700.p 4.4201
800.p 4.5832
900.p 5.0749
1.n 5.7175
However, if I add the "uic" option, the initial voltage becomes 0,
although there is not any specified initial condition:
Gnucap> get circuit.ckt
Gnucap> print tran v(N528849)
Gnucap> tran 0 1n 0.1n uic
#Time v(N528849)
0. 0.
100.p 0.64275
200.p 1.0197
300.p 1.0951
400.p 0.88528
500.p 0.49818
600.p 0.11335
700.p -0.090857
800.p -0.01006
900.p 0.34247
1.n 0.84256
Shouldn't it have given the same results?
Can the initial voltage of N528849 be defined to another value than 0?
Regards,
Xavier
- [Gnucap-devel] JFET and initial conditions,
Xavier Romeuf <=