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Lecture 24 Current Mirrors with Improved Performance_1

# Lecture 24 Current Mirrors with Improved Performance_1 - EE...

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EE 311 Lecture 24 March 5, 2010 & (EEO 311 Lecture 23) 6.12 Current-Mirror Circuits With Improved Performance Zubair Rehman

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2 Lecture 21 Summary for CG Stage Open-Circuit Voltage Gain A vo = v o / v test A vo = 1 + (g m + g mb )r o R in = (r o +R L )/A vo R OUT = r o * [(g m + g mb )R s + 1)] + R s Note that r o and R s can be interchanged: R OUT = R s * [(g m + g mb )r o + 1)] + r o R OUT = R s * A vo + r o & R OUT = r o * A vo + R s Also R OUT for CS Stage with R s > 0
3 6.12.1 Cascode MOS Mirrors I REF = (V CC - V GS1 - V GS4 ) / R Q1, Q2, Q3 & Q4 Identical: I O = I REF

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4 Basic BJT Current Mirror o CE CE C C C B REF o B B C C REF o r V V I I I I I I I I I I I I 1 2 1 2 2 1 1 1 / 2 1 1 / 2 1 1 - + = + = + = + + = β I REF = I C1 + I B1 + I B2 I o = I C2 = I C1 where r o = V A /I C (0V) - + + = - + = - + = A CE CE REF o A CE CE C C A CE CE C C V V V I I V V V I V I V V V I I 1 2 1 2 1 1 2 1 2 1 * / 2 1 1 * 1 * ) 0 ( / β
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6 V BE1 = V BE2 I E1 = I E2 = I E β I = β 2 = β I B1 = I B2 = I E / ( β+129 1 + = = 129 + + 1 + = + = 129 + = 1 + 1 + = + = 1 + = = + = 1 + = Ι = = 2 2 3 Ε β β β β β β β β β β β β α E C o E E B C REF E E E B E B B B E E C C I I I I I I I I I I I I I I I I I I I I 2 3 1 3 3 2 1 3 2 1 ( 2 ( 2 2 * 1 1 2 2
7 By using another transistor Q3. Beta ( β ) can be effectively squared. V BE1 = V BE2 I E1 = I E2 = I E β I = β 2 = β I B1 = I B2 = I E / ( β+129 1 + = = 129 + + 1 + = + = 129 + = 1 + 1 + = + = 1 + = = + = 1 + = Ι = = 2 2 3 Ε β β β β β β β β β β β β α E C o E E B C REF E E E B E B B B E E C C I I I I I I I I I I I I I I I I I I I I 2 3 1 3 3 2 1 3 2 1 ( 2 ( 2 2 * 1 1 2 2

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Lecture 24 Current Mirrors with Improved Performance_1 - EE...

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