dc_coupled2 - EXERCISE Direct-coupled feedback amplifier...

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1 EXERCISE – Direct-coupled feedback amplifier a) Describe the type of feedback and find β and A f ? b) A vf = v o / v i ? c) A v1 = v c1 / v i ? d) Plot the DC and AC lines. e) v imax = ? ANSWER: a) Voltage-shunt (voltage-parallel) feedback β = i f / v o -1 / R f = -1 μ Ω -1 A f = R Mf = v o / i i 1 / β = -R f = -1 M Ω Note: A = R M h fe1 R 2 / R 3 h fe2 R 4 = 40M Ω and A v = R M / R 1 = 400. b) A vf = v o / v i = (v o / i i ) (i i / v i ) = R Mf / R 1 -10 c) Let’s consider the following equalities v o = A vf v i i c2 -v o / R 4 i c2 h fe i b2 i b2 v c1 / R 3 V CC = 12 V h FE = h fe = 200 V BE = 0.7V I CO 0 A V CEsat 0 V 1/hoe = 120k Ω
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2 vf fe i o o c c b b c i o o b b c i o o c i c v A R h R v v v i i i i v v v v i i v v v v v v v A 4 3 2 2 2 2 1 2 2 1 1 1 1 1 1 = = = = = = 100K / 200 / -10K x -10 = 0.5 d) DC equations Base-emitter loop V CC – I BQ1 R f – (I CQ2 + I BQ1 )R 4 – V BE1 = 0 V CC – I BQ2 R 3 – (I CQ1 + I BQ2 ) R 2 – V
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dc_coupled2 - EXERCISE Direct-coupled feedback amplifier...

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