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logarithmic detector amplifier - discrete

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neazoi

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At around the middle of this page http://lea.hamradio.si/~s53mv/spectana/sa.html there is a discrete log detector.
Since it output only up to 100mV max for the full dynamic range, I would like to guild an amplifier for it but using discrete components. Any schematics or ideas are appreciated.
 

Obvious Video amplifier on Fig. 10 is what you want. It's output is 1V/20dB (~4Vmax).
Discrete components does not enable simple realisation with good enough temperature stability.

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Here you have more compact log detector with AD8703 with greater dinamic range:
https://www.qsl.net/n9zia/spec/log_amp.png
 
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I am confused! FiG 9 log detector is discrete. Fig 10 is video amp and is linear and has op amps. Which one are you talking about? I would think their characteristics are matched (Vref if fed between them) so I would use these circuits.
Frank
 
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    neazoi

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Similar log detector as on Fig. 9 is contained in AD8703. Schematics for that SA were first time published at the end of 1998.
 

I am confused! FiG 9 log detector is discrete. Fig 10 is video amp and is linear and has op amps. Which one are you talking about? I would think their characteristics are matched (Vref if fed between them) so I would use these circuits.
Frank

As I said, I am looking for a DISCRETE components amplifier.
The log detector in that page outputs a very low voltage and needs an amplifier.
There is a reason why to use a discrete components log amplifier and this is dynamic range, read the article.
 

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