Building a logarithmic amplifier

[accurate]

Is it possible to build a logarithmic amplifier using a diode like the following figure?



Theorically this circuit follows the formula:



Thank you very much in advance

 

[daddles]

Check out Art of Electronics section 4.14.

 

[OLIVE2222]

here under fine application note

http://www.national.com/an/AN/AN-311.pdf

 

[accurate]

Thank you very much Olive2222 and daddles.

Olive 2222, so it's not possible to build a logarithmic amplifier using the configuration shown in my first post? it seems to me I have to design a more complex circuit.

Daddles I haven't checked this book yet. But I'll do it soon. Meanwhile can you give me an abstract of this section.

 

[OLIVE2222]

Your first post circuit should work, but it's a basic circuit it can probably be handy for simple usages but not, typically, for measurment, as the dynamic range is low.

 

[accurate]

I have just read Art of Electronics section 4.14.

The problem was with the saturation current of diodes which I don't know how to find it. Because each one varies a lot from different diodes.

I have also read that logarithmic circuits need to be calibrated because of Is because Is is unknown and I have to determine it from my lab results and using the thorical formula.

Thank you very much