[sdiy] Log converters

[Tom Farrand]

Walker,

Did you notice that this IC (ADL5306) only comes in a chip-scale
package?  The IC wafer IS the package!  It is 3 x 3mm and there are
solder bumps on the bottom to affix it to a substrate and make
connections.  Nice tiny part if you are building an iPod Nano or
similar.  Is a real bitch if trying to build a one-off.

Many companies offering samples are no longer doing so.  The reason is
that the semi market is getting pretty hot.  I have been waiting for
weeks for STM's newest CORTEX part and am still waiting.  SOP was that
I send an email or make a phone call and the parts magically fall into
my hands the next day.  Now, it is "take a number".  I am glad that
design is coming back to life but our initial schedules did not allow
for long lead times.  Not only that, I am seeing buggier silicon than
before.  Testing quality has really slid downhill on some of the "big"
players, I am sorry to say.


I would suggest slogging through the basics at first pass.  Download
National Semiconductor's AN-30 application note and check that out.
Then I'd look at Horowitz and Hill's book "The Art of Electronics".
Digi-Key has some temperature compensating resistors in stock for
about $0.60 each so that is pretty cheap!  THAT Corp still offers
matched transistors and they are available at Mouser.

If your application is loose, you can make such converters using
discrete transistors (from the same batch) for dirt cheap. If your
need is near-perfection in the transfer function, that will cost more
and likely be a bit finicky with several calibration adjustments to
tweak everything into place.

Peace.
Tom Farrand



On Thu, Jan 7, 2010 at 5:21 PM, Walker Shurlds <walkershurlds at gmail.com> wrote:
>
> Any of yall ever use any kind of IC for log conversion or exponential
> current source?
>
> I'm looking at this; not intended for CV application.
>
> http://www.analog.com/en/fiberoptic/loglimiting-amplifiers/adl5306/products/product.html
>
> (Might actually be antilog... didn't read the datasheet very
> carefully yet.)
>
> Anyway, if not this one then is there anything else similar?  (Since it
> would have hella better temperature compensation built in.)
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