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Old 27th October 2011, 05:43 PM   #1
Atilla is offline Atilla  Norway
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Default Voltage Logarithmic convertor

I saw this while looking into how logarithmic amplifiers work:

A Novel Voltage-to-Voltage Logarithmic Converter with High Accuracy

Has anyone implemented anything similar? The usual log amplifiers seem to require a bit complex thermal compensation, while this idea looks fairly stable.

I need audio signal in, log-scaled voltage out and I've started getting very confused in how to do it. I don't need high-frequency operation that much, neither perfect precision, but I've no idea how bad the standard-issue log amplifier really is.
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Old 27th October 2011, 07:16 PM   #2
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What are you attempting to accomplish?
Audio input and a log d.c. output?
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Old 27th October 2011, 07:28 PM   #3
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http://www.analog.com/static/importe...ets/AD8310.pdf
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Old 27th October 2011, 08:50 PM   #4
Atilla is offline Atilla  Norway
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Yes, exactly that Frank.

Thanks peranders, I just saw that IC and a Maxim IC an hour after I asked. The MAX4206 looks hard to source, but the AD should be easier to find.
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Old 27th October 2011, 09:28 PM   #5
Atilla is offline Atilla  Norway
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I found an AD8307 here, it looks like that'll do fine.
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Old 28th October 2011, 09:53 AM   #6
Frex is offline Frex  France
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Hello Atilla,

Maybe this project could interest you, it's a DIY RMS voltmeter with DC log output
using the AD8307 IC.

Frex.
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Old 28th October 2011, 10:43 AM   #7
Atilla is offline Atilla  Norway
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Thanks a lot Frex, this will help me a lot, indeed. And by the way - great project there!
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Old 28th October 2011, 03:59 PM   #8
Frex is offline Frex  France
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In the case of you would want to build it, i have some bare PCB of this
project available for sale.

Frex.
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