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In the circuit shown below, assume that the voltage drop across a forward biased diode is 0.7 V. The thermal voltage Vt = kT/q = 25 mV. The small signal input vi= Vp cos(ωt) where Vp= 100mV.
[1] The bias current IDC through the diodes is [2 marks]
(A) 1 mA
(B) 1.28 mA
(C) 1.5 mA
(D) 2 mA[2] The ac output voltage Vac is [2 marks]
(A) 0.25 cos(ωt) mV
(B) cos(ωt) mV
(C) 2cos(ωt) mV
(D) 22 cos(ωt) mV
asked in Electronics and Communication Engineering, 2011
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12.
A four – phase and an eight – phase signal constellation are shown in the figure below.
[1] For the constraint that the minimum distance between pairs of signal points be d for both constellations, the radii r1 and r2 of the circles are [2 marks]
(A) r1 = 0.707d, r2 =2.782d
(B) r1 = 0.707d, r2 =1.932d
(C) r1 = 0.707d, r2 =1.545d
(D) r1 = 0.707d, r2 =1.307d[2] Assuming high SNR and that all signals are equally probable, the additional average transmitted signal energy required by the 8-PSK signal to achieve the same error probability as the 4-PSK signal is [2 mark]
(A) 11.90 dB
(B) 8.73 dB
(C) 6.79 dB
(D) 5.33 dBasked in Electronics and Communication Engineering, 2011
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