Designing a Log amplifier

[abinayabaskaran]

  ^{First doubt that arises in every student mind while designing a log amplifier is whether temperature compensation is to be done? And also we know that the amplifier gives logarithmic value of the input but not aware of its practical applications. If u have this doubt just read below:}

 

^{When Log Amplification is required?}

   ^{_{If the input have very high dynamic range (the difference between maximum input value and minimum input value), applying logarithm to the input helps us in easy manipulation.}}

   ^{_{For Example if we are in need to acquire signal from the detector part of a sensor which have large dynamic range. We cannot use normal amplifier which complicates the signal manipulation .So if we amplify the output of log amplifier i.e. after dynamic range compression signal manipulation becomes easier one.}}

 

^{How to design a Log amplifier circuit?}

    ^{Most important circuit component in the amplifier is a bipolar transistor in diode mode or a simple diode.
   As we all know that the base emitter voltage of the Si transistor (VBE) is logarithmically related to the}

^{Collector current of the transistor over a wide range.}

   ^{So the circuit is designed by connecting a transistor across an amplifier IC.}

 

^{What happens if Temperature compensation is not done?}

   ^{Two transistors are used while designing a log amplifier. Practically they both cannot be isothermal. Hence, output gets affected by temperature. To remove this effect thermistor or Senistor is added in the circuit}

[AJISH ALFRED]

Very useful piece of information. Thanks

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