Question

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5. In the multistage amplifier shown below the transistors have large B and assume VBE 0.7 V. Assume that the de output voltage is adjusted to 0. Identify and name the stages of this amplifier. b. Calculate the de bias currents and the de node voltages of the transistors Q. Q2, and Q3 a. +5 V +S V 3.3 kn 100 kn S 100 kn s.6 kn ER-72 n -5 V -5 V

Answer 1

Loop 1 0 -72 I_ref - 0.7 - (-5) = 0 I_res = 5 - 0.7/72 mA = 0.069 mA = 60 uA for current mirror I_out = I_ref I_out = 60 uA Q_1 and Q_2 both are identical so I_E_! = I_E_@ = I_out/2 I_G = I_E_2 = 30uA \r\n v_c_1 = v_c_2 = v_cc- R_C times I_c beta is large so I_c = I_e v_c_1 = v_C_2 = 5 - 100 times 1063 times 30 times 10^-6 = 5 - 1066 times 3 times 106-6 = 2 apply loop 2 5 - 3.3 I_E_3 - v_c_2 = 0 3.3 I_E = 5 - v_C_2 I_E_3 = 3/3.3 mA = 0.909 mA beta large so I_C_3 = I_E_3 loop 3 v_0 = 5 - 5.6 times I_C_3 = 5 - 5.6 times 0.9 = 5 - 5.04 = -0.4 congruence 0 therefore above circuit acting as level shifter.