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其实你可以打开一个ibis模型
3 T8 w% K+ u+ S# N) n0 j查看一个IO buffer的[Ramp]波形
) _ h& W$ b2 R, M( \" w8 K( S. b9 o你会发现有三个波形,对应这里的Typ、min、max
) ?: |& j3 N9 J+ L; A& I; m% Y它的dV值是不同的,因为三根曲线的幅值就不同
2 a- a6 L: {$ v3 u# d所以它的20%~80%电压就不同
- l( n! ?+ e! l$ z' \& I. P2 e当然三根曲线的斜率也不同
7 P8 R+ V5 D& [4 ~袁荣盛 发表于 2009-7-7 12:43 * C4 b4 N6 q" z$ {" _
谢谢这位兄弟,我对这个参数是这样理解,不知对不对7 h4 W* n$ H$ R1 }/ M$ Y
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。' a4 j3 w- C C' O
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。
. e% G/ ^4 k1 b这里的稳态值就是iBIS spec中的 Voltage swing。
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d, h4 u3 }% \- Z0 F9 {, f9 m5 k/ a下面是IBIS spec中[Ramp]的说明,
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7 P+ L& b2 [) L1 zKeyword: [Ramp]
* ~ ^1 ^& k' _, d5 W=======================================================
0 K" T: W. n* E) n2 @& O q; r| Required: Yes, except for inputs, terminators, Series and Series_switch }2 F7 ~1 Z! V8 [ Q) Z- n
| model types3 A! k g1 K6 W0 c
| Description: Defines the rise and fall times of a buffer. The ramp rate! q' g N9 t/ P0 j# m' I" r1 g
| does not include packaging but does include the effects of the
1 X8 w+ ?$ b/ v: x! i# S/ T| C_comp or C_comp_* parameters.
- m& v' s* }3 Z| Sub-Params: dV/dt_r, dV/dt_f, R_load
2 z6 o& w A4 Z/ K0 d( A H| Usage Rules: The rise and fall time is defined as the time it takes the
! k7 M6 B6 k4 [* X| output to go from 20% to 80% of its final value. The ramp4 s T5 I0 r4 H4 H/ ]1 \, [4 k
| rate is defined as:
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) G4 K) ~ }/ m| dV 20% to 80% voltage swing, ]2 K; e' B- |4 M: }
| -- = ----------------------------------------
2 r' {& w; K1 C. i| dt Time it takes to swing the above voltage |
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