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If x(t) ←F.T→ 2 sin ω = X(jω), when 1 + ω x(t) = 1, |t| < 1 0, otherwise
then the Fourier transform of signal y(t)
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4 sin2 ω ω2 -
8π sin2 ω ω2 -
2 sin2 ω πω2 - None of these
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Correct Option: B
First approach:
y(t) = x(t) * x(t)
Y(jω) = X(jω) X(jω)
= | . | ω | ω |
= | ω2 |
Second approach
Given, waveform
slope = | = 1 | 2 |
If
y(t) ←F.T.→ Y(jω)
then
y(t) ←F.T.→ (jω)2 Y(jω) | dt2 |
y′′(t) = δ(t + 2) – 2δ(t) + δ(t – 2)
F{y′′(t)} = ejω2 – 2 + e–jω2
= 2 | ![]() | ![]() | - 2 | |
2 |
= 2.cos 2ω – 2
= 2(cos 2ω – 1)
= 2(1 – 2 sin2 ω – 1)
= 2(– 2 sin2 ω)
= – 4 sin2 ω
Now, (– jω)2 Y(jω) = – 4 sin2 ω
or
Y(jω) = | sin2 ω | ω2 |
Hence, alternative (A) is the correct choice.