A differential pair has per side

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Semiconductor devices and analogue circuits · Semiconductor devices and analogue circuits

Inside the Instrument, Ch The differential pair and the current mirror

Problem

A differential pair has gm=20 mSg_m = 20\,\mathrm{mS} per side, a tail resistance Rtail=50 kΩR_{\rm tail} = 50\,\mathrm{k}\Omega, and nominal collector resistors RC=8 kΩR_C = 8\,\mathrm{k}\Omega that are mismatched by ΔRC/RC=2 %\Delta R_C/R_C = 2\,\%. ((a)) Find the single-ended common-mode gain Acm≈−RC/(2Rtail)A_{cm} \approx -R_C/(2R_{\rm tail}). ((b)) Find the single-ended CMRR, CMRR≈gmRtail\mathrm{CMRR} \approx g_mR_{\rm tail}. ((c)) Find the differential-output CMRR, CMRR≈2gmRtail/(ΔRC/RC)\mathrm{CMRR} \approx 2g_mR_{\rm tail}/(\Delta R_C/R_C), and state which output, single-ended or differential, rejects common mode better here, and by what factor.

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