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I need a temperature compensated logarithmic amplifier

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techie

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Logarithmic amplifier

I need a temperature compensated log amp to convert a logarithmic varying resistance to more or less linear voltage. The temperature compenstation can be done in software if I can know the exact compensation formula with temperature as I already have a temperature sensor on board.

thanks

techie
 

Roscoe

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Hi techi,

i think you can do it in another way. First you must know what type of temp sensor you have, e.g. pt100, type of thermocouple (J K S or so on).

Then look at Maxim and Linear Technologie or other manufactors for special chips for themperature measurement. There are some chips on the market with this feature.

For example: you have an themocouple type K, so you choose the right chip for this and you have a linear voltage output.

Roscoe
 

techie

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Log

I think you did not get my point. Temperature is not a problem. I already have a sensor (thermistor based) and have the temperature value calculated in software. Now I want this value to be applied to a logarithmic amplifier to correct its response for temperature. Since most log amps are based on the log response of Vbe of a transistor and this Vbe is highly temperature dependent. I dont know exactly how to correct the output voltage for temperature. A simple log amp circuit using simple op-amp can be found in any op-amp book or in the n@tion@l semi website. But its temperature dependence is not documented in detail.
 

algilsan

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if i don't bad remember, i think there's a logaritmic amplifier configuration using op amps. Search for this circuit.

i think it's made using an op amp and a pair of transistors.....

Regards
 

bman

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log amp

If temp. compensation can be performed in software, perhaps you can do the log conversion in software too.
 

abba

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try that from ad - it's good working
 

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