h14_lecture10_2

h14_lecture10_2 - Lecture 10 Differential Pair Boris...

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EE 214 Lecture 10 (HO#14) B. Murmann 1 Lecture 10 Differential Pair Boris Murmann Stanford University murmann@stanford.edu Copyright © 2004 by Boris Murmann EE 214 Lecture 10 (HO#14) B. Murmann 2 Overview Reading – 3.5.0, 3.5.3, 3.5.5 (Differential Pair) Introduction – The differential pair is the most widely used two-transistor sub-circuit in analog ICs. As we have already seen last time, using a differential pair as a replacement for a simple common source stage eliminates the need for a precise gate bias voltage (V B ). In addition, its differential input and output voltages are more immune to parasitic signal coupling. Today we will analyze some properties of differential pairs and introduce the notion of common- and differential-mode signal components.
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EE 214 Lecture 10 (HO#14) B. Murmann 3 Differential Pair When V ip =V im , and both transistors are identical, we must have I d1 =I d2 =I TAIL /2 How about V ip =V im =1V versus V ip =V im =2V? – Makes no difference! From a signal perspective, we care only about the difference of the applied voltages – Makes sense to introduce a new variable •V id =(V ip -V im ) I TAIL I d1 V ip I d2 V im EE 214 Lecture 10 (HO#14) B. Murmann 4 Differential and Common Mode (1) We now still need a second variable that describes the potential of nodes V ip and V im with respect to GND – Could choose either V ip or V im More elegant solution –C u t V id in half and define a new independent variable – "Common mode" voltage V ic I TAIL I d1 + V ip - I d2 V id + V im -
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EE 214 Lecture 10 (HO#14) B. Murmann 5 Differential and Common Mode (2) I TAIL I d1 + V ip - I d2 V id /2 + V im - V id /2 V ic im ip id V V V = 2 2 id ic im id ic ip V V V V V V = + = 2 im ip ic V V V + = EE 214 Lecture 10 (HO#14) B. Murmann 6 Coupling Noise Immunity Using differential pairs/signals not only solves the biasing issue, but also mitigates coupling noise issues C couple V ic V aggressor C couple V i V aggressor V im V ip V id (!) Single Ended Signaling Differential Signaling
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EE 214 Lecture 10 (HO#14) B. Murmann 7 Large Signal Transfer Function (1) Let's first do a simple analysis using long channel equations I
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This note was uploaded on 04/17/2008 for the course EE 214 taught by Professor Murmann,b during the Fall '04 term at Stanford.

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h14_lecture10_2 - Lecture 10 Differential Pair Boris...

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