ho19.l16_diff_pair

# ho19.l16_diff_pair - Differential Pair R Dutton Boris...

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1 Lecture 16 Lecture 16 Differential Pair R. Dutton, Boris Murmann R. Dutton, B. Murmann 1 EE114 (HO #19) Stanford University 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 R. Dutton, B. Murmann 2 EE114 (HO #19)

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2 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 I TAIL I d1 V ip I d2 V im R. Dutton, B. Murmann 3 EE114 (HO #19) – Makes sense to introduce a new variable •V id =(V ip -V im ) Differential and Common Mode (1) We now still need a second variable that describes the I d1 I d2 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 I TAIL R. Dutton, B. Murmann 4 EE114 (HO #19) Common mode voltage V ic + V ip - V id + V im -
3 Differential and Common Mode (2) I d1 I d2 im ip id V V V = I TAIL 2 2 id ic im id ic ip V V V V V V = + = im ip V V + R. Dutton, B. Murmann 5 EE114 (HO #19) + V ip - V id /2 + V im - V id /2 V ic 2 ic V = Coupling Noise Immunity

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ho19.l16_diff_pair - Differential Pair R Dutton Boris...

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