Download EMT 112/4 (Analogue electronics 1)

EMT112
EMT 112/4 (Analogue electronics 1)
Tutorial 5
Question 1
Assume 1 = 120, 2 = 150, VA = ∞ and VBE (ON) = 0.7 V, find:
(a) The small-signal parameters, g m and r for both transistors.
(b) The overall small-signal voltage gain AV 
vO
.
vS
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EMT112
Question 2
Figure 2 shows an amplifier in cascode configuration where a common-base stage (Q2) is
being driven by a common-emitter stage (Q1).
(a)
Draw the circuit under dc condition and determine the quiescent currents ( I CQ1
and I CQ 2 ) of both transistors.
(b)
Draw the small-signal equivalent circuit of the complete amplifier and perform an
ac analysis to show that the approximate overall small-signal voltage gain is given
by the expression;
Av 
(c)
vo
  g m1 RC // RL 
vi
If the peak-to-peak value of the input voltage vi is 30 mV, determine the
approximate peak-to-peak value of the output voltage vo .
Assume 1   2    150 , VBE1active  VBE 2active  VBE active  0.7 V
VA1  VA2  VA   , VT  26 mV and VCC  15 V .
Figure 2
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EMT112
Question 3
Determine the input impedance Ri and output impedance Ro of the two-stage amplifier
shown in Figure 3.
Assume VCC  5 V , VEE  5 V , 1  127 ,  2  200 , VBE active for both transistors is
0.7 V and VT  26 mV .
Figure 3
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