16_Lecutre

16_Lecutre - EE114 Lecture 16 Lecture 16 Differential Pair...

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EE114 Lecture 16 R. Dutton, B. Murmann 1 EE114 (HO #20) Lecture 16 Differential Pair R. Dutton, B. Murmann Stanford University R. Dutton, B. Murmann 2 Significance The differential pair is the most widely used two-transistor circuit in integrated circuits – Many circuits rely on the “computation” of the difference between two voltages EE114 (HO #20)
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EE114 Lecture 16 R. Dutton, B. Murmann 3 General Analysis of the 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 EE114 (HO #20) R. Dutton, 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 – Cut 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 - EE114 (HO #20)
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EE114 Lecture 16 R. Dutton, 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 + = ! EE114 (HO #20)
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16_Lecutre - EE114 Lecture 16 Lecture 16 Differential Pair...

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