I need a temperature compensated logarithmic amplifier

[techie]

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]

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]

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.

 

[gabby]

Hi
Try the site of anlogdevices:

here you can find a lot of log amp:
**broken link removed**

also look on thier app for temp sensor and log amp you can find a lot
of info how to design .(they have a lot of experience in analog design

tell us if you find what you need.

Best regards.

 

[algilsan]

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]

log amp

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

 

[abba]

try that from ad - it's good working

 

[boot_strap]

Re: Logarithmic amplifier

Well ithink a good suggestion is refering to chapter 9 of schaums outline of electronics
on this link