※ [本文轉錄自 Grad-ProbAsk 看板 #1FUlidle ]
作者: kela12340 (Avanlandis) 看板: Grad-ProbAsk
標題: [理工] 【電子學】MOS差動對
時間: Tue Apr 3 21:29:07 2012
題目:
In this example we consider the design of the current source that
supplies the bias current of a MOS differential amplifier.Let it be
required to achieve a CMRR of 100dB and assume that the only source
of mismatch between Q1 and Q2 is a 2% mismatch in their W/L ratios.
Let I = 200uA and assume that all transistors are to be operated at
Vov = 0.2V. For the 0.18-um CMOS fabrication process available.
VA'=5 V/um.
(1)If a simple current source is utilized for I,what is the
required value of "channel length"?
(2)If a cascode current source is utilized,what's the channel length
of the two transistors in the cascode?
---------------
(1)小題書上的算法求gm時: gm = 2ID/Vov = 2 x (I/2) /Vov = 2 x 0.1 /0.2
= 1m A/V，
但(2)小題時 gm = 2I/Vov = 2 x 0.2 / 0.2 = 2m A/V ，
想請問為何current source的構造從單一MOS變成CASCODE的形式時，流過的I
卻變為兩倍?
目前的想法解讀是:因為cascode兩顆MOS串聯，所以Leq = 2L，所以電流將會是
使用一個MOS的0.5倍..，但是這...只會讓電流變小阿= ="(今天上課老師
剛好有提到這個，但不是電子學的課..)
感謝各位!!
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◆ From: 1.175.152.180
※ 編輯: kela12340 來自: 1.175.152.180 (04/03 21:50)
※ 發信站: 批踢踢實業坊(ptt.cc)
※ 轉錄者: kela12340 (1.175.141.174), 時間: 04/04/2012 10:41:31