In a CMOS differential pair with bias current IB, the small-signal differential transconductance Gm_diff equals which?
AGm_diff = IB·gm always at balance condition
BGm_diff = 2·gm of one transistor at IB/2
CGm_diff = gm/2 only at balance condition
DGm_diff = gm of one transistor (each at IB/2)
Answer & Solution
Correct answer: D. Gm_diff = gm of one transistor (each at IB/2)
Differential pair (Sedra-Smith Ch.8): for small differential input v_id, one side current rises by gm·v_id/2, the other drops by the same. Output ΔI = gm·v_id.
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