1. Noise and Interference Any signal or phenomena which degrades signal to noise ratio (S/N). External 1.Thermal noise (raw or amplified) 2.On-channel unwanted emissions (interference) 3.Atmospheric noise 4.Man made noise Internal 1.Distortion 2.Harmonics 3.Shot Noise (carrier transit noise) 4.Flicker (1/f) Noise 5.Intermodulation For now, we will concentrate on Thermal and Shot Noise, as they: Are pervasive Are of similar magnitude Have similar spectral properties

2. Spectral Density Thermal and shot noise are broad spectrum (white) random noise processes, characterized by “flat spectral density”, which has two important implications: 1.Equal energy available at all frequencies 2.Noise power entering a system is proportional to the system’s acceptance bandwidth (usually, the bandwidth of one received channel). P N (watts) = ( ? ) x BW(hz) Fundamental Property of White Noise: Spectral Density N 0 (watts/Hz = joule) N 0 = Pwr/BW = kT for thermal noise. P th (watts) = kTB k = Boltzman’s constant = 1.38 x 10 -23 (j/K) ; T = Absolute Temp (K)

3. Thermal Noise Voltage P th (watts) Ideal Bandpass Filter B ~ RR V th (rms) Voltage Spectral Density: Current Spectral Density: For frequencies within B For frequencies outside of B Thermal noise source associated with random electron motion inside the resistance “R”

4. Shot Noise Shot Noise is represented by a random noise current generated in a semiconductor junction, in parallel with the junction dynamic resistance r d = 0.026v/I DC (for silicon). q = 1.6 x 10 -19 Coul (electron charge) Since noise currents and voltages are random and uncorrelated (orthogonal), they must always be considered as RMS values when multiple noise sources are present: I s (rms) rdrd Thevenin is alive and well in Prescott Arizona,... and the rest of the universe.

5. 20 k  V n (rms) + 10 VDC - Example Ideal Bandpass Filter B = 100 kHz B

6. rdrd Ideal Bandpass Filter B 100 kHz ~ 20 k  V th I shot VnVn 20 k  I th Open Circuit Noise Voltage Note that the thermal noise represents a small contribution to the total noise voltage/current compared to the shot noise.