Anybody know of a site that explains what exactly a logarithmic
amplifier is and how and where it is applied? I'm thinking in
particular of the Analog Devices offerings.....

Thanks,

Tim

Have you tried a Google search? I get LOTS of hits that look like
they'd tell you what you want. Try also the ap notes on the Analog
Devices (and TI/Burr-Brown) web sites. (I'm assuming you really do
mean log amps, and not the linear-in-dB power monitor ICs from Analog
Devices [and others].)

Cheers,
Tom

From: on Jul 21, 5:55 pm

Anybody know of a site that explains what exactly a logarithmic
amplifier is and how and where it is applied?

Not known by me. A logarithmic AMPLIFIER is a rare bird in
finished goods and the "successive detection" type is much
more common.

The best text I know of is "Logarithmic Video Amplifiers" by
Richard S. Hughes, then at the China Lake (CA) Naval Weapons
Center, Artech House 1971, published by Horizon House-Microwave,
Dedham, Massachusetts. "Video" in this context is up to 60
MHz plus...

Texas Instruments once made a Log Video Amplifier dual in a
dual-inline-package. Used that for some log-video R&D
circuitry in the 1970s. It went out of production, probably
due to low demand.

It's use was/is mainly in radar signal processing, considering
that the radar return varies a terrific number of db in
signal strength. One use that I had it for was to find the
3 db down point on an RF pulse which had a large peak signal
strength string. It is now used as a power output indicator
and, in Europe, has been the central part of a wide dynamic
range power meter for hams.

I'm thinking in
particular of the Analog Devices offerings.....

Those seem to be "successive detection log amplifiers." The
purpose there is to do a demodulation in amplitude of the
RF using successive non-linear amplifiers, each with its own
detector, the detector outputs summed. Summation of detector
outputs is a logarithmic characteristic compared to linear
input.

There IS a successive SUMMATION amplifier, or at least WAS,
and that does much the same although it sums the RF without
demodulation. Speaking from some experience, they are a
total #$%^!!!! to keep phase-stable over amplitude variations.
Others have found that. Not too many of those products were
available as ready goods.