logarithmic amplifiers.pptx

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1. A PRESENTATION ON LOGARITHMIC AMPLIFIERS PRESENTED BY; BIJOYDIPTA GHOSH ELECTRICAL ENGINEERING 2 ND YEAR(3 RD SEM) 11101622011

2. INTRODUCTION Logarithmic amplifiers, also known as log amps , are electronic devices designed to convert an input signal's exponential relationship into a linear output response. They are commonly used in various applications, including signal processing, communication systems, and measurement instruments. The primary function of logarithmic amplifiers is to compress a wide dynamic range of input signal amplitudes into a more manageable linear range at the output. This is particularly useful when dealing with signals that span several orders of magnitude, such as in Radio Frequency communication or audio applications. By utilizing logarithmic amplifiers, it becomes easier to accurately process and measure signals that vary widely in amplitude.. The logarithmic amplifiers' ability to convert exponential signals into linear ones makes them valuable components in various electronic systems, contributing to improved signal-to-noise ratio and overall performance.

3. CONTENTS TOPICS COVERED HERE: WHAT IS LOGARITHMIC AMPLIFIER APPLICATIONS OF LOGARITHMIC AMPLIFIERS CIRCUIT DIAGRAM TRANS DIODE CONFIGURATION ( RELATION BETWEEN OUTPUT VOLTAGE WITH THE INPUT VOLTAGE AND THE FIXED RESISTENCE) Conclusion references

4. WHAT IS LOGARITHMIC AMPLIFIER A log amplifier is an amplifier for which the output voltage V0 is k times the natural log of the input voltage Vi, this can be expressed as: V0=k log ((Vi/ Vr )) ,where Vr is the normalization constant in volts and K is the scale factor. The term log amp is generally used in communication technology, refers to calculate log of an input signal’s envelope. All logarithmic amplifiers must therefore specify a signal range over which they will “log”.

5. APPLICATIONS OF LOGARITHMIC AMPLIFIERS Logarithmic Amplifiers can be used in many ways,such as: To perform mathamatical operations like multiplication , division , exponentiation. To calculate the db value of a given quantity As a true RMS converter

6. CIRCUIT DIAGRAM

7. TRANS DIODE CONFIGURATION According to the virtual short concept, the voltage at the inverting input terminal of an op-amp will be equal to the voltage at its non-inverting input terminal. So, the voltage at the inverting input terminal will be zero volts. The nodal equation at the inverting input terminal’s node is − (O-Vi)/R1 + If=O If=Vi/R1---------->Equation 1 The following is the equation for current flowing through a diode, when it is in forward bias − If=Is e^( Vf / nVt )--- ----->Equation 2 where, Is  is the saturation current of the diode, Vf  is the voltage drop across diode, when it is in forward bias, Vt  is the diode’s thermal equivalent voltage. The KVL equation around the feedback loop of the op amp will be − O- Vf -Vo=O Vf =-V0 Substituting the value of  Vf in Equation 2, we get − If=Is e^(-V0/ nVt ) (Vi/R1)=Is e^(-V0/ nVt ) ln (Vi/R1Is)=-V0/ nRt V0=- nRtln (Vi/R1Is) Hence,the output voltage Vo will be proportional to the natural logarithm of the input voltage Vi for a fixed value of resistance R1. V0 has a negative sign, which indicates that there exists a 180  phase difference between the input and the output.

8. CONCLUSION In summery ,Dc log amp ICs have evoled into small ,easy-to-use, cost effective circuits nicely suited for certain analog designs. The logarithmic function convinently compresses wide dynamic range signals and linearizes sensors with(semi-) exponential transfer functions.Calibration procedures can enhance log-amp performance, but are not necessery in all applications.

9. REFERENCES WEBSITES VISITED : www.wikipedia.com www.powershow.com BOOKS VISITED: ELECTRONICS:ANALOG AND DIGITAL, BY NAGRATH, PHI, 2004 ELECTRONIC PRINCIPLES, BY MALVINO,6/ e,tmh Integrated electronics, by millman & halkies,tata mcgrow hill.

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