Set15 - Noise & Noise Rejection Noise...

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Unformatted text preview: Noise & Noise Rejection Noise & Noise Rejection Noise & Noise Rejection Noise & Noise Rejection Noise Sources Characterizing Noise Signal-to-Noise Ratio (SNR, S/N) Power Spectral Density Slide 1 ME365 Noise & Noise Rejection Galen King Purdue University Modes of Interference Noise Rejection: Filtering Modulation Shielding & Grounding Differential Amplifier Averaging Noise Noise Noise Noise Noise Noise is any unsteady component of the measurement signal that causes the instantaneous value of the signal to differ from the instruments rendition of the true value. Slide 2 ME365 Noise & Noise Rejection Galen King Purdue University Time x ( t ) v v x t s t n t ( ) ( ) ( ) = + Actual Signal Noise Noise Sources Noise Sources Noise Sources Noise Sources Internal Temperature-induced random noise in conductors (Johnson noise) Random current fluctuations in transistors (Shot noise) Slide 3 Flicker noise External AC Interference Communication Interference Switching Interference Mechanical/Structural Vibration ME365 Noise & Noise Rejection Galen King Purdue University Average Signal Power Average power (in Watts) dissipated when voltage signal is connected to a 1 resistor: ssume the actual signal and the noise are independent of Noise Characterization Noise Characterization Noise Characterization Noise Characterization x t T x t dt T 2 2 1 ( ) ( ) = Slide 4 ME365 Noise & Noise Rejection Galen King Purdue University Assume the actual signal s ( t ) and the noise n ( t ) are independent of one another: Root Mean Square (RMS) voltage of a signal is: Ex: For x ( t ) = A sin( t + ), the average power of x ( t ) is: v x t s t n t 2 2 2 ( ) ( ) ( ) = + Signal Power Noise Power dD x t x t ( ) ( ) rms = 2 Signal-to-Noise Ratio (SNR, S/N) Characterizes the noisiness of a particular signal, x ( t ) = s ( t ) + n ( t ): NR is usually expressed in decibels (dB): Noise Characterization Noise Characterization Noise Characterization Noise Characterization S N Signal Power Noise Power = = s t n t 2 2 ( ) ( ) Slide 5 ME365 Noise & Noise Rejection Galen King Purdue University SNR is usually expressed in decibels (dB): The uncertainty of a measurement is the inverse of the SNR. S N Signal Power Noise Power or S N Signal RMS Noise RMS dB dB rms rms s t n t s t n t = = = = 10 10 20 20 10 10 2 2 10 10 log log ( ) ( ) log log ( ) ( ) Noise Characterization Noise Characterization Noise Characterization Noise Characterization System Noisiness The noisiness of a system (device) is called the Noise Figure ( NF ). It is defined to be the ratio between the input and output SNR: Measurement ystem (Device) Input Output Slide 6 ME365 Noise & Noise Rejection Galen King Purdue University It is desirable to design a measurement system (device) that has a...
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Set15 - Noise & Noise Rejection Noise...

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