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解决spice在tran时的internal timestep too small问题的方法
9 \( B s% F& [1 k, ~1 [5 hTransient Analysis: 也就是一般的暂态分析.一般错误的* C& Z! _" S, a& A/ Z& H+ h
Message 为:-"Internal timestep too small."
( p* C3 O, B) S$ ^6 L另外,也会常看到 "Singular Matrix", or "Gmin/Source Stepping
6 [8 Y- j4 m' T9 V9 IFailed" 这样的 Error Message.解决这个问题没有一定的方法,根
) a3 }2 |4 f; m t$ D) ` h& \7 D$ t据我们的经验,我们大致把它们说明如後:
2 ~7 L# m3 ~4 L% W, m1. 电路错误:指的是由使用者本身电路,有不正常的接线或短路等,例如将电源
8 b1 S9 A- c) |" D% z6 V" ?7 g接到输出端,而造成SPICE在运算的时候无法收敛.根据Ref[38] 的建议,请
# q2 c4 S8 K/ w你确认以下之状况:
9 P, H H$ u! [# `! ?' zMake sure that all of the circuit connections are valid. Check for
& m% S. W0 @1 Gincorrect node numbering or dangling nodes. Also, verify component
$ o2 q+ k. g0 rpolarity.6 {4 L) a7 C, X# W
Make sure you didn't use the letter O instead of a zero (0).: y9 `: E# F/ _3 `+ W( U6 J# K
Check for syntax mistakes. Make sure that you used the correct SPICE
* X5 h* @9 w* g2 Lunits (i.e. MEG instead of M(milli) for 1E6).# B/ t/ j" _# _( {
Make sure that there's a DC path from every node to ground.+ |$ J% d* n* O+ C& P% h3 m& ~) J' C
Make sure that there are at least two connections at every node.! {$ O0 C- p2 d- \
Make sure that there are no loops of inductors or voltage sources. ~: Y4 L( T+ } F" z* [+ Q, D
Make sure that there are no series capacitors or current sources.8 z' V6 ~1 u; X
Place the ground (node 0) somewhere in the circuit. Be careful when e: F- l' v, w# B# @( @; M
you use floating grounds; you may need to connect a large resistor from
7 K4 Q a0 }9 g% [4 N! xthe floating node to ground.5 D9 X4 }* R# w6 o
Make sure that voltage/current generators use realistic values, and: v r/ Z& {' B! `
verify that the syntax is correct.
0 M% V& k0 V1 u9-46 VLSI 设计概论 / 实习
+ k. d: \$ d, g( F% Y% O OMake sure that dependent source gains are correct, and that B element( U2 t [1 x( o: Y
expressions are reasonable. If you are using division in an expression,9 \6 T& _- k2 b" ?
verify that division by zero cannot occur.
/ M! [' ~8 y# c) X0 CMake sure that there are no unrealistic model parameters; especially if9 C4 D' J9 d; w( k* @. x! B( Z: c, a
you have manually entered the model into the netlist.! n' u" Q' V& D# p5 f5 J: `) V& M
Make sure that all resistors have a value. In SPICE 3, resistors without) W; U8 V u1 S, `$ T. z& d l! X
values are given a default value of 1k Ohm.
9 \# @4 e& U, B- ]- Z1 aNegative capacitor and inductor values are allowed in SPICE 3. They+ r2 ]/ D2 U7 h, }: Z+ t. D, \
will not be flagged as an error, but can cause timestep problems,) s* k( w- X/ e* Q# f
depending on the topology of the circuit.
, ~* \, [( G Y& \2. 检查Feedback : 所指的是在序向逻辑电路中所产生的,你可以检查一下你的" q+ n# z" e+ p$ b7 T) U
电路的FeedBack Path的Delay,在不影响电路功能的情形下,是否可以调快一- E- Y6 C" [# [3 j5 r/ A" M) ]
点或慢一点.4 r: [9 G% m7 T
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