Electronics/Noise in electronic circuits

Electrical Noise any unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals. Classification Based on Origin External noise Atmospheric Extraterrestrial solar Cosmic Industrial Internal noise Thermal Agitation Noise Shot Noise Transit Time Noise Flicker Noise Miscellaneous Sources Thermal noise Thermal Agitation Noise Also known as Johnson noise or White noise. where k = Boltzmann's constant = 1.38x10-23J/K T = absolute temperature, K = 273 + °C δ f = bandwidth of interest Pn = maximum noise power output of a resistor Shot Noise shot noise#In electronic devices where in = r.m.s. shot-noise current e = charge of an electron = 1.6x10-19C ip = direct diode current δ f = bandwidth of system Noise Calculations Addition due to several sources noise voltages: , ...and so on, then where Rtot = R1+R2+... Addition due to Cascaded Amplifier stages Req = R1+R'2 Analog Noise Models CMOS BJT Noise in digital circuits: Methods of reducing noise Differential signaling Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analogue signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, PCI Express and USB. Good grounding An ideal signal ground maintains zero voltage regardless of how much electrical current flows into ground or out of ground. When low-level signals travel near high currents, their return currents shouldn't be allowed to flow in the same conductor. Otherwise, noise such as AC ripple on the high current will modulate the low-level signal. References Kennedy, George 'Electronic Communication Systems' , 3rd Ed. 0-07-034054-4