A basic bipolar current mirror is set by a reference current

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 basic bipolar current mirror is set by a reference current Iref=0.80 mAI_{\rm ref} = 0.80\,\mathrm{mA}. Both transistors have βF=80\beta_F = 80 and VA=120 VV_A = 120\,\mathrm{V}. The output transistor's collector sits ΔVCE=4.0 V\Delta V_{CE} = 4.0\,\mathrm{V} above the reference transistor's fixed collector-emitter voltage. ((a)) Find the output current Iout=Iref(1+ΔVCE/VA)/(1+2/βF)I_{\rm out} = I_{\rm ref}\left(1+\Delta V_{CE}/V_A\right)/\left(1+2/\beta_F\right). ((b)) Find the mirror's output resistance at this operating point.

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