Noise calculation presentation
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This document discusses the calculation of noise in communication systems. It begins by defining noise as unwanted energy that interferes with signals. It then provides an example calculation of noise at the input of a two-stage cascade amplifier. The key steps are: 1) Calculate the noise voltage due to the output resistance of each stage and transfer it to the input of the next stage. 2) Calculate the equivalent input resistance by adding the input resistances and noise resistance contributions from each stage. 3) This equation can then be used to calculate the total noise resistance at the input of the first stage.
![Practical Noise Calculation R 1 =R i1 +R i2 R 2 = (R o1 *R i3 )/(R o1 +R i3 )+R i4 R 3 = R o2 Now from the equation (1) R eq = R 1 +( R 2 / A 1 ²) + ( R 3 / A 2 ² A 1 ²) R eq = ( R i1 + R i2 ) + [{( R o1 * R i3 )/( R o1 + R i3 )+ R i4 }/ A 1 ²] + ( R o2 / A 2 ² A 1 ²)](https://image.slidesharecdn.com/noisecalculationpresentation-101212074651-phpapp01/85/Noise-calculation-presentation-10-320.jpg)
Noise calculation presentation
- 1. Welcome to my Presentation
- 2. Noise Calculation Presenter: Md. Anik Arefin Nahin Id: 081-19-846 Sec:A Dept. Of ETE, DIU
- 3. Noise: In communication systems noise is an unwanted energy tending to interfere with the easy and correct reception and reproduction of the wanted signals. In other words the noise is an error or undesired disturbance of a useful information signal introduced before or after the detector and decoder. No system can be designed which is perfectly free of noise and noise plays a very important part of study of electrical communications.
- 4. Noise Calculation Noise calculation is necessary to determine and reduce noise in a system. There are several ways to calculate noise in different systems. We’ll discuss about Noise at a two stage equivalent cascade amplifier.
- 5. Noise Calculation This is a figure of equivalent two stage cascade amplifier. Here R1 and R2 are subsequent input resistances and R3 is output resistance A1 and A2 are respectfully 1st stage and 2nd stage gain.
- 6. Noise Calculation Now noise voltage due to R 3 is E n3 So, E 3 =√(4KTB R 3 ) This noise voltage can be transferred to the input point of the second stage by, En 3 /A 2 =E’ n3 =√(4KTBR 3 )/A 2 =√(4KTBR’ 3 ) So R’ 3 = R 3 /A 2 ²
- 7. Noise Calculation Now R’ eq =R 2 +R’3 =R 2 + (R3/A 2 ²) Similarly R’ 2 = R’ eq / A 1 ² =(R 2 /A1²) + (R 3 / A 2 ²A 1 ²) So, R eq = R 1 + R’ 2 = R 1 +(R 2 /A 1 ²) + (R 3 / A 2 ²A 1 ²) ……… (1)
- 9. Practical Noise Calculation Now, from the circuit diagram given left R i1 =1 st input resistance of 1 st stage R i2 =2 nd input resistance of 1 st stage R o1 =output resistance of 1 st stage R i3 =1 st input resistance of 2 nd stage R i4 =2 nd input resistance of 2 nd stage R o2 =output resistance
- 10. Practical Noise Calculation R 1 =R i1 +R i2 R 2 = (R o1 *R i3 )/(R o1 +R i3 )+R i4 R 3 = R o2 Now from the equation (1) R eq = R 1 +( R 2 / A 1 ²) + ( R 3 / A 2 ² A 1 ²) R eq = ( R i1 + R i2 ) + [{( R o1 * R i3 )/( R o1 + R i3 )+ R i4 }/ A 1 ²] + ( R o2 / A 2 ² A 1 ²)
- 11. Decision To solve the equation it is necessary to calculate from the right side of the circuit and to solve practical problems it should start from left. This make it very easy. This equation can be extended to any number of amplifier stages in cascade. Using this equation the noise resistance, actually present in the input of 1 st stage, can be calculated and so as the noise.
- 12. Thank You