circuit to measure signal level / log amp / log math

Mar 14, 2006 2 Replies
S

I want to Accurately (within 1dB or so) determine the signal strength of a signal coming into an amplifier circuit. The input signal level can vary dramatically, and the circuit includes AGC. I am thinking that I need to do the following:



The attenuation level of the AGC circuit is logarithmically related to a current output from the AGC circuit. To accurately convert this current to a voltage that represents Attenuation, and to provide for temperature compensation of the log conversion, I would use a Maxim MAX4206 Log Amp.



I would then convert the Output Signal to DC, convert it to log, and add it to the AGC voltage obtained above.



What all am I overlooking?



Is there a simpler way?



Thanks, Scott Kelley


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C

For +/- 1 dB accuracy, I'd suggest that you measure the signal level before the amplifier. I realize that would require a separate amplifier, but that is what I would explore. Of course, if this is a "one-of" design problem, that is a different matter. Then, I'd try working with the amplifier and the AGC voltage. However, it might not be easy to meet your spec.

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S

The signal level can vary pretty dramatically. At least 60 dB, possibly a good deal more.

What would be the advantage of doing it this way, and how would you deal with the large dynamic range?

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