-
Open an PowerSI sample file
-
Disable all Capacitor
-
Disable all Capacitor
but Add VRM
-
Enable all
Capacitor (ideal) and Add VRM
-
Enable all
Capacitor (realistic) and Add VRM
-
Compare
Z-profile of 6X1uF and 6X1nF
-
Open an PowerSI sample file
psi.spd
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Disable all Capacitor
Disable all nets,
but VCC and GND.
Active Bottom
layer.
Click the color
box, set VCC--orange, GND--Green.
Setup \ Circuit/Linkage
Manager,disable all decoupling
capacitors, and select the circuit (sink1) to generate VCC-GND port
Set sweep frequency
1K~3GHz, and run simulation.
Save as the file as
psi_no decap.spd.
Save the simulation
result as psi_no decap.bnp.
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Disable all Capacitor
but Add VRM
-
Enable all
Capacitor (ideal) and Add VRM
Ideal Capacitor
model (3.3nF)
加上幾個3.3nF decap,第一個諧振頻點位置往右移了
-
Enable all
Capacitor (realistic) and Add VRM
realistic capacitor
因為引入了寄生電感效應,第一個諧振頻點位置略為往左移了
-
Compare Z-profile
of 6X1uF and 6X1nF
6.1 原例中的6顆decap離主IC蠻遠的,所以不管ideal
decap電容值怎麼加大(3.3nF~100nF~0.1uF~10uF),Z-profile沒有明顯改變
6.2 重新在IC的IO
pin旁,就近放6顆realistic decap (分別是100pF, 1nF, 10nF, 1uF)
做這個實驗時,電容模型的正確性很重要,不能隨便輸入,否則會看到錯誤的趨勢。取得電容S參數模型
PCB板級電容一般處理400MHz以下的Z,再高頻的部份,PKG放上去會壓下來,再更高頻就要靠on-die
decap。為什麼我不說板級電容可以處理到1GHz呢? 因為實務上不可能放一顆100pF的電容在IC
pin上,除非是內嵌在封裝裡,否則400M~1GHz這頻段的decoupling靠PCB板上放電容效果不是很好,因為decoupling
path上會有loop inductance。
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