Q1 In the amplifier circuit below all transistors have beta = 100 and V BE(ON) =
ID: 1810864 • Letter: Q
Question
Q1
In the amplifier circuit below all transistors have beta = 100 and V BE(ON) = 0.7V. Q 1 and Q2 have r0 rightarrow infinity and Q3 and Q4 have |VA| = 200V. Describe the function of the transistors Q3 and Q4 and calculate the value of R required to ensure the circuit supplies the 2mA emitter biasing current. Using the Hybrid - pi model in the small-signal circuit, calculate the small-signal output resistance R out seen from the junction "a" connecting the emitter circuits of Q l and Q2. Use the Hybrid- pi model to draw the small signal equivalent half-circuits for both the differential mode and common-mode inputs.Explanation / Answer
1. Q3 and Q4 are parts of current mirrors. They help in attaing a constant current source , as Iee = i_Ref.
i_ee = i_Ref = 2mA.
R = (12 - 0.7 )/2 =5.65 K ohm.
2. Rout = Ro of Q4= Va / Ic =200 / 2 = 100 Kohm.
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