推 jsp0520:推認真回~ 07/09 21:11
推 gggould:感謝熱心分享 p幣奉上 07/10 00:50
→ deathcustom:囧，其實我P幣很多，用不到QQ 07/10 00:53
※ 引述《gggould (evanescent)》之銘言：
: 隨便在網路上找一個cascode current mirror的圖
: http://tinyurl.com/799z53b
: 請問一下
: 從m9 drain / m7 source看進去的阻抗
: 應該是多少
: 有沒有比較直觀的看法嗎
: thanks
我們要先來研究一下
將電路從M7/M9中間砍斷
把M9的ro9並聯到M7的Rin7
Rin7 = (R_cs+ro7)/(1+gm7ro7) = inf (R_cs = inf)
Rin = ro9 || Rin7 = ro9
看M7這個CG amplifier
Gm = 1/Rin
Ro = ro7 + ro9 + gm7ro7ro9 ~ gm7ro7ro9
Vo7/Ii7 = Vo/(Vi/Rin) = Rin*Av7 = Rin*(1/Rin)*(Ro||R_cs)
= Ro||R_cs = gm7ro7ro9||R_cs = gm7ro7ro9 (R_cs = inf)
Vo7 = Vin9
Io9 = gm9*Vin9 = gm9Vo7
Io9/Ii7 = AB = gm7ro7gm9ro9
整個迴授電路的Rin(在M7/M9這點)
因為是電流 => shunt
Rif = Rin/(1+AB) ~ ro9/gm7ro7gm9ro9 = 1/gm7ro7gm9#
假如R_cs != inf, R_cs ~ ro
Rin = ro9 || Rin7
AB = Io9/Ii7 = gm9*Vo7/Ii7 = gm9*(Vo7/Vi7)*Rin = gm9*(Ro||R_cs)
Rif ~ (ro9 || Rin7)/[gm9(Ro||R_cs)]
= [(ro9*Rin7)/(ro9 + Rin7)]/[gm9RoR_cs/(Ro + R_cs)]
= ro9*Rin7*(Ro + R_cs)/[gm9*Ro*R_cs*(ro9 + Rin7)]
=ro9*(R_cs + ro7)*(gm7*ro7*ro9 + R_cs)/[gm7*ro7*gm9*gm7*ro7*ro9*R_cs(ro9+Rin7)]
=A7*ro9(R_cs+ro7)(A7*ro9+R_cs)/[A7*A7*A9*R_cs(A7*ro9+ro7+R_cs)]
~A7*ro9(2ro7)(A7*ro9)/(A7^2*A9*ro7*A7*ro9)
=2ro9/A7*A9 = 2/gm7ro7gm9
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※ 編輯: deathcustom 來自: 122.116.95.114 (07/09 20:54)