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757.
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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758.
The channel resistance of an N – channel JFET shown in the figure below is 600Ω when the full channel thickness (tch) of 10μm is available for conduction. The built – in voltage of the gate P+N junction (Vbi) is -1V. When the gate to source voltage (VGS) is 0 V, the channel is depleted by 1 μm on each side due to the built – in voltage and hence the thickness available for conduction is only 8μm.
[1] The channel resistance when VGS = 0V is : [2 marks]
(A) 480Ω
(B) 600Ω
(C) 750Ω
(D) 1000Ω[2] The channel resistance when VGS = -3V is : [2 marks]
(A) 360Ω
(B) 917Ω
(C) 1000Ω
(D) 3000Ωlast reply by CpjJwWHV • 13 years ago • asked in Electronics and Communication Engineering, 2011
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759.
The input – output transfer function of a plant H(S) = 100/[s(s+10)2]. The plant is placed in a unity negative feedback configuration as shown in the figure below.
[1] The signal flow graph that DOES NOT model the plant transfer function H(S) is : [2 marks] 
[2] The gain margin of the system under closed loop unity negative feedback is
[2 marks]
(A) 0 dB
(B) 20 dB
(C) 26 dB
(D) 46 dBasked in Electronics and Communication Engineering, 2011
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760.
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761.
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762.
