# solution

Question 1: DC Biasing and Small-Signal Analysis of BJT Amplifiers (100 marks) Consider the BJT common-emitter amplifier in Figure 1. Assume that the 2N3904G transistor has the following parameters: ÃŸ-206, VBE-0.7V and the Early voltage VA-1000V. VCC 5.0V RB1a I You ean use muliple resistors f the value you RC want is not availsble in the kt Vc Vload Rload Cin 01 10? Vb 2N39040G V1 4.7pf RB2 IRE1 RE2CE 0.01Vpk 1kHz You can use mutiple resistors ifthe value you want is not available in the kit Figure 1 BJT CE amplifier (a) Design the DC biasing circuit so that lc 2 mA, VCE 2.5 V, VE- 0.5 V and Vc- 3 V. [20 marks] (b) Use the DC operating point analysis in MultiSim to calculate lc, Vc, VB, Ve and Vce. Compare your results with your hand calculations from (a) and explain any differences. [15 marks] (c) Confirm by calculation that the transistor is operating in the active mode. [5 marks] (d) Calculate the transistor small signal parameters, gm, rn and ro [10 marks] (e) Assuming that the frequency is high enough that the capacitors appear as short circuits, calculate the mid-band small signal voltage gain A, -load [15 marks] (f) Use the AC sweep analysis in MultiSim to simulate the amplifier small signal voltage gain load over the frequency range of 10 Hz to 100 MHz, using a decade sweep with 10 points per decade. Set the AC voltage source to a peak voltage of 0.01 V. Compare the simulated gain with the gain calculated in (e) above. Also, explain the shape of the simulated gain curve (why does the gain decrease at low frequencies and at high frequencies?) [15 marks]

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