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Unformatted text preview: ME365 Noise and Noise Rejection 1 • Noise Sources • Characterizing Noise – Signal-to-Noise Ratio (SNR, S/N) – Power Spectral Density • Modes of Interference • Noise Rejection: – Filtering – Modulation – Shielding & Grounding – Differential Amplifier – Averaging Noise & Noise Rejection ME365 Noise and Noise Rejection 2 Noise Noise is any unsteady component of the measurement signal that causes the instantaneous value of the signal to differ from the instrument’s rendition of the “true value”. Time x ( t ) ݔ ݐ ൌ ME365 Noise and Noise Rejection 3 Noise Sources • Internal – Temperature-induced random noise in conductors (Johnson noise) – Random current fluctuations in transistors (Shot noise) – Flicker noise • External – AC Interference – Communication Interference – Switching Interference – Mechanical/Structural Vibration ME365 Noise and Noise Rejection 4 • Average Signal Power Average power (in Watts) dissipated when voltage signal is connected to a 1 Ω resistor: – 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:...
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- Fall '07
- Nf, Noise Rejection