Question 1. Determine the voltage V_O in the circuit of FIGURE 1 for:

(a) β = 50, V_BE = 0.7 V

(b) β = 250, V_BE = 0.7 V.

Fig 1

Comment on the significance of your result.

Question 2. State the effects of negative feedback, when applied in a voltage amplifier, upon:

- the overall amplification

- variations in transistor gain

- non-linearity

- output impedance.

Question 3. Estimate the power developed in the 8 ? speaker of the circuit of FIGURE 2 for a 1 kHz sinusoidal input signal of 100 mV peak. All capacitors may be assumed to act as a short circuit at the frequency of operation.

Compare your estimate with that derived from a PSpice simulation.

[A Simetrix version of the circuit can be downloaded from the module's Learning Materials on BlackBoard.]

Fig 2.

Question 4. FIGURE 3 shows the circuit of a multistage amplifier. Identify the stages and describe the operation and principle features of the amplifier. You should also make an estimate of the maximum output current of the amplifier.

Fig 4.

Question 5. FIGURE 4 shows an amplifier circuit. operation and performance of the circuit. should:

Write a short report on the In completing the report you

- Explain the operation of the circuit and in particular the role of resistors R₁ and R₂.

- Build the circuit in PSpice and use it to determine:

(i) the quiescent value of V_out.

(ii) the voltage gain for a 100 mV, 1 kHz , input signal.

- Sketch the small-signal equivalent circuit of the amplifier and use it to estimate the voltage gain. Compare your answer with that of (ii) above.

- Attempt to calculate the quiescent value of V_out. Compare your answer with that given by the PSpice model. Try to explain any discrepancies.

[Hint : Apply the appropriate equation (1 or 2) of Lesson 4.]

Fig 4.

N.B The parameters used by Simetrix for the transistor model can be obtained in the Schematic Command window. Use the function key F11 to reveal this window. But first import the description of the model by selecting from the menu bar;

Simulator/Import Models.../Import direct copy.

Note also that V_P = V_TO and I_DSS = β × V_P² .