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GATE 2021 IN – Question 58

Analog Electronics · Diodes and transistor circuits · 2 marks · Numerical answer

All transistors shown are matched with current gain $\beta=20$. Neglect the Early effect. Current $I_{o4}$ is ______ mA.

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Correct answer: 1 to 1

Explanation

All five transistors have the same VBE and hence collector current IC. The 1.25-mA reference supplies the diode-connected collector plus all five base currents: Iref=IC+5IC/β=IC(1+5/20)=1.25IC.

Thus each output, including Io4, is **1 mA**. Finite base-current loading must be included.