ot noise (10.28) Shot noise is the name given to noise generated in active devices such as valves, transistors and integrated circuits. It is caused by the random varying velocity of electron movement under the influence Pu=kTBw (10.29) of externally applied potentials or voltages at the terminals or electrodes. (10.30) It is similar to thermal noise in that it has a gaussian distribution and a flat power spectrum. It differs, however in that it is not directly affected by temperature. Its magnitude is proportional to the square Noise units and measurements 10/11 root of the direct current through the device and thus may be a It is considered to be a voltage increase of 12 dB or more above the function of signal amplitude. r.m.s. noise for a period of 12 ms or less. The r.m.s. value of the shot noise current is given by Equation This type of noise may be caused by a number of sources such as 10.32, where I is the average anode current; B is the effective the switching of relays in electro-mechanical telephone exchanges. bandwidth; and e is electronic charge. Although these "clicks and pops" are annoying to the human ear, it is reasonably tolerant. However impulse noise may cause many (10.32) serious error rate problems on data or digital circuits. The effects of impulse noise can be alleviated by the use of a wide band clipping circuit followed by a band limiting filter. This proce- dure first reduces the amplitudes of the spectral components and 10.8.5 Partition noise then reduces the number of components. Partition noise occurs in multi-electrode devices such as transistors 10.8.9 Flicker noise and valves. It is due to the current through the device being divided between the various electrodes. Flicker noise is sometimes known as low frequency (1/f) noise or excess noise. It is because of its unusual increase at very low 10.8.6 Intermodulation noise frequencies that it is also called low frequency noise. Its cause is associated with contact and surface irregularities in Intermodulation noise is due to the prese