Question 2.2.48: Zero mean Gaussian noise of variance N is applied to a half ...

Zero mean Gaussian noise of variance N is applied to a half wave rectifier. The mean squared value of the rectifier output will be

(a) Zero                                                    (b) N/2

(c) N \sqrt{z}                                                    (d) N

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Half wave rectifier is given as
y = x for x 0
= 0 for x< 0

\text { So } f(y)=\frac{1}{2} \delta(y)+\frac{1}{\sqrt{2 \pi N}} e^{\left(-y^{2} / 2 N\right)}

 

\begin{aligned}E\left(y^{2}\right) &=\int_{0}^{\infty} y^{2}+(y) d y \\&=\int_{0}^{\infty} y^{2}\left[\frac{1}{2} \delta(y)+\frac{1}{\sqrt{2 \pi N}} e^{\frac{-y^{2}}{2 N}}\right] d y \\&=0+\int_{0}^{\infty} \frac{y^{2}}{\sqrt{2 \pi N}} e^{\frac{-y^{2}}{2 N}} d y\end{aligned}

 

\begin{aligned}&\text { Let that } \frac{y}{\sqrt{N}}=t \\&d y=\sqrt{N} d t \\&E\left[y^{2}\right]=\frac{1}{\sqrt{2 \pi N}} \int_{0}^{\infty} N t^{2} e^{\frac{-t^{2}}{2}} \sqrt{N} d t \\&=\frac{N}{\sqrt{2 \pi}} \int_{0}^{\infty} t^{2} e^{\frac{-t^{2}}{2}} d t \\&E\left[y^{2}\right]=\frac{N}{2}\end{aligned}

Hence, the correct option is (b)

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