Lecture 25-Supply Insensitive Biasing

# Lecture 25-Supply Insensitive Biasing - Lecture 25 Supply...

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EE 214 Lecture 25 (HO#33) B. Murmann 1 Lecture 25 Supply Insensitive Biasing Boris Murmann Stanford University murmann@stanford.edu Copyright © 2004 by Boris Murmann

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EE 214 Lecture 25 (HO#33) B. Murmann 2 Overview Reading – 4.4.2 (Supply Insensitive Biasing) Introduction – Throughout this course, we have ignored the question on how to generate the reference bias currents used in most of our circuits. Today, we will examine a variety of current reference implementations, with primary focus on supply independence.
EE 214 Lecture 25 (HO#33) B. Murmann 3 Poor Man's Bias Issue: Current is essentially proportional to V DD – E.g. if V DD , varies by X%, bias current will roughly vary by the same amount R V V V I I OV t DD IN OUT =

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EE 214 Lecture 25 (HO#33) B. Murmann 4 "V t " Referenced Bias By using a sufficiently large device, we can make V OV << V t, and achieve 2 ox IN t 2 OV t 2 1 GS OUT R L W C I 2 V R V V R V I µ + + = 2 t OUT R V I Question: By how much will I OUT change given some variation in V DD ?
EE 214 Lecture 25 (HO#33) B. Murmann 5 Sensitivity The sensitivity of a parameter y to a change in parameter x can be approximately found using y x ! S x y y x x / x y / y x / x y / y = = In our case, we are looking for % 1 . 7 V 1 . 0 V 6 . 0 V 1 . 0 2 1 . g . e V V V 2 1 I I I I 1 S S S 1 OV t 1 OV IN OUT OUT IN I I I V I V OUT IN IN DD OUT DD = + + = Not bad, but also not all that great…

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## This note was uploaded on 01/16/2011 for the course EE 214 taught by Professor Murmann,b during the Spring '04 term at Stanford.

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Lecture 25-Supply Insensitive Biasing - Lecture 25 Supply...

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