a little difficult! Assume that Q1 and Q2 are identical transistors with beta =

Question

a little difficult!

Assume that Q1 and Q2 are identical transistors with beta = 9, Rs = 300 Ohm, RF = 10 k Ohm VCC = 3.6V, and the VBE = 0.8V for each NPN transistor. Calculate the collector currents through Q1 and Q2. Draw a small signal model corresponding to this circuit. Note: You don't need to calculate the parameter values. Do not forget to consider Early effect. Derive an expression for the input impedance, Rin, of the circuit shown. Express your answer symbolically i.e. in terms of parameters such as gm2, ro1, r pi 1 etc. Do not forget to consider Early effect. Assume that ac coupling capacitors (or dc blocking capacitors) behave like shorts for signals of interest.

Explanation / Answer

we have two equations here,

b(1 + b)*Ib1 = Ic2-------------------------------1

and

(1+b)^2*Rs*Ib1 + 10^4 Ib1 = 2--------------------2

solving the two we get

Ib1 = 5*10^-5 A

or Ic1 = b*Ib1 = 9*5*10^-5 = 4.5*10^-4 A

and Ic2 = 4.5 mA from equation 1.

b.

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