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其实你可以打开一个ibis模型
# o1 E Z: Q% N4 N查看一个IO buffer的[Ramp]波形1 P6 W) M4 l2 z5 g$ O
你会发现有三个波形,对应这里的Typ、min、max% o# f4 L1 b7 n' k' ~8 S
它的dV值是不同的,因为三根曲线的幅值就不同
/ z1 s5 i. O3 C3 Y- @2 D0 u5 `所以它的20%~80%电压就不同
' D. w. V/ q5 Y. K当然三根曲线的斜率也不同" _: G+ V( Z. H) @! K: f- S t9 v
袁荣盛 发表于 2009-7-7 12:43 . `1 O$ F: |2 p' W' l% X0 i y
谢谢这位兄弟,我对这个参数是这样理解,不知对不对
6 V+ e) \& w4 R% h W! N0 c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。5 H6 `8 ~& z9 p1 N6 V' }6 \5 ^3 k3 x
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。$ Q Z% a% M9 q& n& h/ Q8 I# O
这里的稳态值就是iBIS spec中的 Voltage swing。
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0 X, a& t* ~+ x7 I( o1 x下面是IBIS spec中[Ramp]的说明,
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" k6 v& L9 g( [, WKeyword: [Ramp]
3 f+ [4 M# y1 H: `3 `" B=======================================================# P, j, v4 c" K4 N6 c. \. v5 V1 C
| Required: Yes, except for inputs, terminators, Series and Series_switch
6 f. h- W# R [3 F; S' | k| model types
$ c+ R1 }2 L8 ] d* u" J3 c| Description: Defines the rise and fall times of a buffer. The ramp rate
! N/ n+ I" U) E4 V7 H* c! A| does not include packaging but does include the effects of the. z& I* `: a! R& T, g8 U, V0 N: T
| C_comp or C_comp_* parameters.! S6 N! t) A4 [7 v# Q& f0 a8 y
| Sub-Params: dV/dt_r, dV/dt_f, R_load0 p2 Z2 ?' a) T6 M5 _1 {+ T2 w
| Usage Rules: The rise and fall time is defined as the time it takes the4 ~" i' k$ u$ d6 ~3 ^ J2 h8 }
| output to go from 20% to 80% of its final value. The ramp# z% C8 J2 j% g/ p& |' ~" ~7 x
| rate is defined as:' F" q. k/ {( z) a# X5 {
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% S# J3 ^, i4 ~| dV 20% to 80% voltage swing
7 F- T$ d" }( n' C9 Y- z- |# B5 E) Q| -- = ----------------------------------------
# y. i8 R3 J/ g| dt Time it takes to swing the above voltage |
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