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logarithmic amplifier (aka log converter) application

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robismyname

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quick question on Analog's Devices logarithmic amplifier (aka log converter). In the part spec it says:

"The essential purpose of a log amp is not to amplify, though amplification is utilized to
achieve the function. Rather, it is to compress a signal of wide
dynamic range to its decibel equivalent"

http://www.analog.com/static/imported-files/data_sheets/AD8307.pdf


So its called logarithmic because the output is in db?

What is the difference between a logarithmic amplifier and a linear amplifier?

Provide brief application of one or both
 

kh4n

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linear amp is for increasing your rf signals amplitude. but logamps mainly used for detecting power level, ie it gives you a dc output for different levels of rf input as it is shown in fig.9 in the datasheet. you can transfer this dc to an adc later to an fpga, etc. or you can use dc level with opamps to build your AGC(automatic gain control) circuitry. these are the most common approaches.
and ADI`s low cost low freq. logamps are widely used for power detection apps.
 

dean_winchester

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the logarithmic amplifier will compress the signals.. more like Expansion and Compression curve in Digital communication so that to increase the SNR of a signal.
So, basically the purpose of logarithmic amplifier is to sense the small voltage input, amplify it and compress it to a level so that signal to noise ratio level is met and in this process you have not lost the original signal.
linear amplifiers have easy job of just amplifying the input and giving the output without any signal conditioning.
 

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