ch09 - Chapter 9 Cascode Stages and Current Mirrors 9.1...

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1 Chapter 9 Cascode Stages and Current Mirrors 9.1 Cascode Stage 9.2 Current Mirrors

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CH 9 Cascode Stages and Current Mirrors 2 Boosted Output Impedances       S O S m out E O E m out R r R g R r R r r R g R 1 || || 1 2 1
CH 9 Cascode Stages and Current Mirrors 3 Bipolar Cascode Stage   1 2 1 1 1 2 1 1 2 || || )] || ( 1 [ r r r g R r r r r r g R O O m out O O O m out

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CH 9 Cascode Stages and Current Mirrors 4 Maximum Bipolar Cascode Output Impedance The maximum output impedance of a bipolar cascode is bounded by the ever-present r between emitter and ground of Q 1 . 1 1 max , 1 1 max , 1 O out O m out r R r r g R
CH 9 Cascode Stages and Current Mirrors 5 Example: Output Impedance Typically r is smaller than r O , so in general it is impossible to double the output impedance by degenerating Q 2 with a resistor. 2 1 1 2 2 O O outA r r r r R

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CH 9 Cascode Stages and Current Mirrors 6 PNP Cascode Stage   1 2 1 1 1 2 1 1 2 || || )] || ( 1 [ r r r g R r r r r r g R O O m out O O O m out
CH 9 Cascode Stages and Current Mirrors 7 Another Interpretation of Bipolar Cascode Instead of treating cascode as Q 2 degenerating Q 1 , we can also think of it as Q 1 stacking on top of Q 2 (current source) to boost Q 2 ’s output impedance.

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CH 9 Cascode Stages and Current Mirrors 8 False Cascodes When the emitter of Q 1 is connected to the emitter of Q 2 , it’s no longer a cascode since Q 2 becomes a diode-connected device instead of a current source. 1 2 1 2 1 1 2 2 1 1 2 2 1 2 1 1 || || 1 || || 1 1 O m O m m out O m O O m m out r g r g g R r r g r r r g g R
CH 9 Cascode Stages and Current Mirrors 9 MOS Cascode Stage   2 1 1 2 1 2 1 1 O O m out O O O m out r r g R r r r g R

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CH 9 Cascode Stages and Current Mirrors 10 Another Interpretation of MOS Cascode Similar to its bipolar counterpart, MOS cascode can be
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This note was uploaded on 04/05/2010 for the course EE EE taught by Professor Ee during the Spring '10 term at Korea Advanced Institute of Science and Technology.

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ch09 - Chapter 9 Cascode Stages and Current Mirrors 9.1...

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