Chapter 6 Differential and Multistage Amplifiers2

Biasing mechanism for icscont d current mirror

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Biasing mechanism for ICs(cont d) Current-mirror circuits with improved perfor mance Ø A bipolar mirror with base-current compensatio n Ø The wilson current mirror Ø The current steering circuits Ø The widlar current source
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The Basic BJT Current Mirror β β β 2 1 1 2 + = + = REF o I I E REF E o I I I I 1 2 1 + + = + = β β β β
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A Simple BJT Current Source. Disadvantages: 1) Increasing I o …… 2) Decreasing I o …… CQ A o on BE CC REF REF o I V r R R V V I I I = = - = 02 ) (
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Current Steering REF REF REF REF BE EB EE CC REF I I I I I I I I R V V V V I 3 2 4 3 2 1 2 1 = = = = - - + =
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Current-Mirror Circuits with Improved Performance Two performance parameters need to be improved: a. The accuracy of the current transfer ra tio of the mirror. b. The output resistance of the current so urce.
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Current Mirror with Base-Current Com pensation 2 2 1 1 β + 2245 REF o I I
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The Wilson Bipolar Current Mirror 2 2 1 1 β + 2245 REF o I I 2 o o r R β ( 29 E o E REF I I I I 1 1 2 1 2 + = + + + = β β β β β
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The Widlar Current Source [ ] o E m o o REF E T o r r R g R I I R V I ) // ( 1 ) ln( π + 2245 = E o BE BE o REF T BE BE S o T BE S REF T BE R I V V I I V V V I I V V I I V V + = = - = = 2 1 2 1 2 1 ln ln ln
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