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lecture_09_current_sources

lecture_09_current_sources - Handout#9 EE 214 Winter 2009...

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B. Murmann, B. Wooley EE215 Winter 2008-09 1 Current Sources Handout #9 EE 214 Winter 2009 B. Murmann and B. A. Wooley Stanford University B. Murmann, B. Wooley EE214 Winter 2008-09 2 Current Sources If Q 2 is in the forward-active region, then I C2 I C1 = I S2 e qV BE /kT 1 + V CE2 V A2 ( ) I S1 e qV BE /kT 1 + V CE1 V A1 ( ) = I S2 I S1 1 + V CE2 V A2 1 + V CE1 V A1 ! " # $ % & V CC Q 2 R V o = V CE2 + Q 1 I ref I o = I C2 + V BE where V Ai is the “Early” voltage of Q i Basic Current Mirror
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B. Murmann, B. Wooley EE214 Winter 2008-09 3 If V CE1 << V A1 I C2 I C1 ! I S2 I S1 1 + V CE2 V A2 ! V CE1 V A1 " # $ % & Base Current Error I ref = I C1 + I B1 + I B2 = I C1 + I C1 ! F1 + I C2 ! F2 If I S1 = I S2 and ! F1 = ! F2 = ! F , then I C1 " I C2 and Output Resistance R out = r o2 = V A2 I C2 = V A2 I o I ref ! I C2 + 2 ! I C2 " F # I C2 = I ref (1 + 2 " F ) B. Murmann, B. Wooley EE214 Winter 2008-09 4 Mirror w/ Base Current Gain V CC Q 2 R V o + Q 1 I ref I o Q 3 I E3 If I S1 = I S2 and ! F1 = ! F2 = ! F3 = ! F , then I C1 " I C2 and ! I E3 = I C1 " F1 + I C2 " F2 !
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