Lecture 12

Lecture 12 - Lecture 12 OUTLINE Cascode Stage Reading...

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1 Lecture 12 – Slide 1 EE105, Fall 2013 Prof. Ming C. Wu Lecture 12 § OUTLINE Cascode Stage § Reading: Chapter 9.1 Lecture 12 – Slide 2 EE105, Fall 2013 Prof. Ming C. Wu Ideal Current Source § An ideal current source has infinite output impedance. § How can we increase the output impedance of a BJT that is used as a current source? Equivalent Circuit Circuit Symbol I-V Characteristic + - V I 1 I I V 1 I N I N R
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2 Lecture 12 – Slide 3 EE105, Fall 2013 Prof. Ming C. Wu § Recall that emi+er degenera0on boosts the impedance seen looking into the collector. This improves the gain of the CE or CB ampliFer. However, headroom is reduced. Boos0ng the Output Impedance R out = 1 + g m R E || r π ( ) ! " # $ r O + R E || r EE E VI R = Lecture 12 – Slide 4 EE105, Fall 2013 Prof. Ming C. Wu Cascode Stage § In order to relax the trade-of between output impedance and voltage headroom, we can use a transistor instead oF a degenera0on resistor: § V CE For Q 2 can be as low as ~ ±.4V ( soL satura0on ) ( ) 1 2 1 1 1 2 1 1 2 || || )] || ( 1 [ r r r g R r r r r r g R O O
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Lecture 12 - Lecture 12 OUTLINE Cascode Stage Reading...

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