Lecture08_Current_Sources_2up

Lecture08_Current_Sources_2up - EECS240 Spring 2008 Lecture...

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EECS240 – Spring 2008 Lecture 8: Current Sources Elad Alon Dept. of EECS EECS240 Lecture 8 2 Bias Current Sources What makes a current source a current source? High output impedance Other important properties: Voltage range (V min ) Noise Accuracy Techniques: cascoding, gain boosting
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EECS240 Lecture 8 3 Bias Current Source Is this a “good” bias current source? EECS240 Lecture 8 4 Current Mirror Better approach: current mirror
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EECS240 Lecture 8 5 Noise M2 adds noise Choose small M (power), or Filter at gate of M1 Current source FOMs Output resistance R o Noise resistance R N Active sources boost R o , not R N () o o v o m N N B m B m m B d d on r R M a r M g R f R T k f M g T k f g M g T k i M i i = << + = + = = + = + = + = 1 1 1 1 4 1 4 4 1 0 1 1 1 2 2 1 2 2 2 2 1 2 γ EECS240 Lecture 8 6 Noise cont’d I n 2 from transistor current source much larger than real R with same output impedance So why do we use transistors as current sources?
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EECS240
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This note was uploaded on 05/23/2008 for the course EECS 240 taught by Professor Eladalon during the Spring '08 term at University of Calgary.

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Lecture08_Current_Sources_2up - EECS240 Spring 2008 Lecture...

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