QUESTION 1:
Considering the two stage amplifier below;
(a) Calculate the DC values VB1, VC1, VE1, IC1 at quiescent conditions relative to 0V.
(b) Calculate the DC values VB2, VB3, VE3, IC2 at quiescent conditions relative to 0V.
(c) If the voltage at the output, under quiescent conditions, is not equal to zero volts, what adjustments would you make to the circuit, in component value choice, to correct this? Show your calculations and give the new component value.
(d) What Class of amplifier is this circuit operating in, as determined by the output configuration? Estimate the maximum power this amplifier can deliver into the 50 ohm load.
[Note : R1 = 22k, R2 = 2k2, R3 = 1k2, R4 = 160, R5 = 68, Ci = 2.2uF]
(Let β = hfe)
QUESTION 2:
Considering the above circuit in Question 1; (a)What is the purpose of R5?
(b) Sketch its small signal equivalent circuit diagram. (Hint: As the pushpull output are complementary and carry the signal independently you can ignore one half (either Q2 or Q3) for the small signal circuit diagram.)
(c) If the voltage gain is set by only the common-emitter stage, then, determine the voltage gain of the amplifier Vout/ Vin.
(Note that the load affects the equivalent output resistance to the CE stage, thus changing the gain!)
(d) Calculate the critical frequency breakpoint provided by the input capacitor Ci and sketch the overall frequency response (Bode plot) for this amplifier over the range 1Hz - 500kHz.
(e) Plot the response using AC Analysis in MicroCap.
QUESTION 3:
(a) Determine the output voltage range for the above circuit having an input voltage of +25mV to - 25mV, for both extreme settings of the reference variable resistor (pot) on the second stage.
(b) Discuss instrumentation amplifiers explaining their differences from operational amplifiers
(c) For the oscillator below, if C1 = 10nF, C2 = 22nF, Rr = 10k and R1 = 22k, R2 = 10k, calculate the value of Rf for the circuit to maintain a sinusoidal output, and the operating frequency.
QUESTION 4:
(a) Sketch the waveforms for at nodes X and Y on the same time base, indicating clearly the thresholds at which switching occurs.
(b) Explain the operation of the circuit below and sketch the approximate waveforms at nodes P, Q, R and V. Do them one under the other to show their correct time relationships. (Let TP = ? = RC)
c) Explain the mode of operation of the switched mode power supply (SMPS) circuit below and by looking up data sheets, determine the output voltage and oscillator frequency.
