Lou Posted November 2, 2004 Report Share Posted November 2, 2004 HelloMany years ago I've seen an application of a converter IC (ICL7106 style) displaying a dB output without any explicit log converter.The circuit was based on a special connection of the input, reference and integrating pins, but I do'nt quite remember how it worked or where it was published.Does anybody have details about such a circuit?Thanks Quote Link to comment Share on other sites More sharing options...
Olihou Posted November 11, 2004 Report Share Posted November 11, 2004 Is the output you have in mind digital or analog?If just for analog, there are functional circuits using op amps and diodes, as far as I can recall.Have you search for it in the cyber? Quote Link to comment Share on other sites More sharing options...
Lou Posted November 12, 2004 Author Report Share Posted November 12, 2004 No, it's digital: the ADC displays dB's instead of mV, and I did obviously search the web as well as specific resources, but without results. Quote Link to comment Share on other sites More sharing options...
Olihou Posted November 13, 2004 Report Share Posted November 13, 2004 Hello LouHow about this? See if it helps.http://www.national.com/an/AN/AN-30.pdfThe log amplifier output gives a DB equivalent of the input voltage.An ADC would be required should you need the digital form.Oli Quote Link to comment Share on other sites More sharing options...
MP Posted November 15, 2004 Report Share Posted November 15, 2004 A simple op-amp with a NPN transistor and small switching diode in the feedback loop makes a logarithmic amplifier. You also need a small cap there to keep the circuit from going into oscillation.It is called a transdiode logarithmic amplifier. Try this in your word search and you should find the information you are looking for.MP Quote Link to comment Share on other sites More sharing options...
Lou Posted November 15, 2004 Author Report Share Posted November 15, 2004 Thanks Oli and MP, but what I want is precisely to avoid a separate log converter; I know that the DVM chip is able to implicitly perform the conversion, but I don't remember the trick.Lou Quote Link to comment Share on other sites More sharing options...
MP Posted November 16, 2004 Report Share Posted November 16, 2004 Lou, I have not seen the project you are mentioning, but when you find it, please post it for others. Thanks,MP Quote Link to comment Share on other sites More sharing options...
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