 Hello friends, myself Ilya Archanjane, assistant professor from Department of Electronics, Walsh and Institute of Technology, Sulapur. Today we are going to see the chapter noise. So what are the learning outcomes from this topic? The learning outcomes are we the students can explain effect of noise and analyze different types of noises. They can compute signal to noise ratio, noise figure, noise temperature. So we will see what is meant by noise. So what is a noise? So the definition itself gives us the idea about noise. It is defined as an unwanted signal which interferes with the original message signal and corrupts the parameter of the message signal. So what it does? It leads to alteration of message signal. It mostly likely affects the signal in the channel or at the receiver. In the digital signal to noise affects, it causes rise in bit errors in information. So what are the different sources of noise? Noise can originate from variety of sources. So the two different sources of noises are natural and manmade. Also noise can be generated internally as well as externally. So sources of noises in that we are going to see what exactly is meant by external noise. There are number of external noises. These are basically categorized under three types. First one is atmospheric noise which is also called as natural noise. Second one is extraterrestrial noise which is called which is also categorized as national noise. Third one is industrial noise which is categorized as manmade noise. So atmospheric noise basically it is referred as static noise. It occurs due to electrical disturbances such as lightning. Lightning causes as we know lightning causes due to electrical discharge hence this affects the communication signal also. This electrical discharge results in transient electrical signal. The transient electrical signal then generates harmonic energy which travels long distance hence atmospheric noise majorly affects the frequencies which are below than 30 MHz. So it becomes less severe above 30 MHz that means the atmospheric noise basically affects the frequency which are less than 30 MHz. These noises are occurring in space hence these are again divided into two basic types. First one is solar noise and second one is cosmic noise. So solar noise primary source of solar noise is sun. As we know sun generates wide range of signals in a broad spectrum. This spectrum includes frequencies basically these are used in communication. The noise radiations produced by sun basically these vary with respect to time. Second one is cosmic noise these the source of this noise is stars. Noise from stars are generally called as cosmic noise. It has a greater impact for a frequency range of 15 to 150 MHz. That means the cosmic noise majorly affects the communication signal which lies in the frequency range of 15 to 150 MHz. Industrial noise noise produced due to automotive ignition such as ignition systems, electrical motors and generator brushes. So it is also occurring due to the electrical equipment which is turning on and off this is also called as a transient noise. As these noise are industrial these come under or these are categorized as man-made noise and hence these can be controlled. Internal noise these noise are generated internally basically these are generated due to electrical components such as registers, diodes, transistors. Low noise these interfere weak signal. So internal noises basically these are low frequency noise and hence they interfere weak signals or affect the weak signals. As we know register noise is directly proportional to the temperature as temperature will increase the noise in the register will also increase and vice versa. Since noise contains high frequency it levels it level can be its level can be minimized by passing the main information signal through a filter which is called as a band pass filter. These filters are also known as tuned circuits. So types of internal noises are thermal noise, short noise, partition noise, low frequency noise which is called as flicker, high frequency and transit time noise. So thermal noise electrons in the conductor as we know they possess varying amount of energy and it varies according to the temperature. Hence small fluctuations in these energy can produce small voltages in the conductor. These random variations basically produced thermal agitation the thermal agitation which is produced due to the electrons is basically called as is called as thermal noise or Johnson noise. The average noise power here which is calculated is proportional is directly proportional to bandwidth and absolute temperature of conductor. Short noise basically as we know we assume that there is a current flowing through the diode transistor under DC conditions and it is constant every time. As current consists of electrons and holes the fluctuations in number of electrons or holes is called as short noise. The spectrum density is as same as that of thermal noise. Also the mean square noise current basically depend directly on DC component of the current. Hence short noise also depend on operating conditions. Short noise can be calculated as I n square 2 bracket I plus 2 I 0 q into bandwidth B w is the bandwidth where I n is noise component I is direct current I 0 is reverse leakage current and q is the charge and B w is the effective noise bandwidth. Partition noise these occur basically when current gets divided into two parts. The partition of the current basically results in fluctuation of the total current. If a transistor is considered then there is a noise due to the random way due to the random motion of the carriers which are crossing from emitter base to emitter collector junctions and if we consider a FET then the noise occurs in as a thermal noise in conduction band. Leakage current also plays an important role because it produces small fluctuations which basically give rise to short noise. Low frequency noise or flicker these are these are the noise which occur below a frequency which is less than in kilohertz. The spectrum of these noise increases as the frequency goes on increasing. Hence noise varies inversely proportional to the frequency. In semiconductors the flicker noise arise due to carrier density, conductivity and material use. When DC current flows through the semiconductors fluctuations occur and these fluctuations basically give rise to the flicker noise. The mean square value of this flicker noise voltage is basically proportional to the square of the DC current flowing through the semiconductor material. High frequency noise or transient time noise these occur due to the carriers when the carriers or we can called as electrons when they cross the conduction band then such kind of noise occurs and these noise are called as transient time noise when signal frequency is high periodic time becomes very small. Hence some of the carriers are diffused back to the source that is emitter. Hence the conductance varies with respect to the frequency as the conductance increases so as the noise spectrum density increases at high frequencies. So, these are the references for you people for the further study. Thank you for watching the video.