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其实你可以打开一个ibis模型
7 C3 r/ j; l$ N+ I查看一个IO buffer的[Ramp]波形
; [/ ]1 W+ |7 J! `' ?- M! S; a7 I你会发现有三个波形,对应这里的Typ、min、max
+ Q& N1 i$ y* F5 j2 [* V& B它的dV值是不同的,因为三根曲线的幅值就不同
1 |9 w& x! B4 }3 H2 ^; _所以它的20%~80%电压就不同3 D+ B( R' e+ I/ E+ D' }
当然三根曲线的斜率也不同; I9 }$ @% Y- j- q
袁荣盛 发表于 2009-7-7 12:43 : d; x) C" y3 v" a; f) G& w( R! a: ^
谢谢这位兄弟,我对这个参数是这样理解,不知对不对; [/ ~. |" A3 E) a3 k8 H
从[Ramp]参数可以得到四个信息:tr(20%-80%);压摆率;输出电压稳态值;buffer的输出阻抗信息。4 D8 G' t% c) m9 {, e, k
buffer输出电压的稳态值等于输出阻抗和50ohm的分压,因为typ、min、max情况下的输出阻抗的不同,因此稳态值也不同,从而dV=(20%-80%)*稳态值也不同。0 b( H+ t: Q; s: B; V
这里的稳态值就是iBIS spec中的 Voltage swing。6 |% M- l; Z7 d! `- U E Y' j
7 Y3 I7 u f+ N. Q, m9 l# m6 h$ H下面是IBIS spec中[Ramp]的说明,
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, q& l& W5 @( J0 J% C0 oKeyword: [Ramp]/ s- O& [; L7 J+ a8 E
=======================================================
0 Q8 D0 I9 _/ A6 |4 N+ W# d| Required: Yes, except for inputs, terminators, Series and Series_switch& f* j( N+ _# [! A2 V% u/ q: k
| model types
# c8 o# `% I* a8 e% z/ w/ w3 O V! I| Description: Defines the rise and fall times of a buffer. The ramp rate+ J; C, C4 M# @+ d @, G/ c; h
| does not include packaging but does include the effects of the
* O: \; }* F2 n- W- b7 M# L| C_comp or C_comp_* parameters.% R6 k( l, z3 D( L$ E: J% E9 e6 S
| Sub-Params: dV/dt_r, dV/dt_f, R_load7 \6 |) v2 ^4 j0 ]8 n" z: z
| Usage Rules: The rise and fall time is defined as the time it takes the( u. g1 |4 n5 T$ G, \8 J
| output to go from 20% to 80% of its final value. The ramp
# {3 S2 I3 B/ @) P, P$ M. L0 }7 }| rate is defined as:
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1 u1 N! ]' p1 s( s% h| dV 20% to 80% voltage swing* o0 e, E9 s' c/ D
| -- = ----------------------------------------
9 W( C( L/ o# Q! x1 [| dt Time it takes to swing the above voltage |
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