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From: "Kevin White"
References: <3DE35202.firstname.lastname@example.org> <3DE3FF0D.8BFA8115@us.ibm.com>
Subject: Re: antilog amplifier
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
NNTP-Posting-Date: Thu, 28 Nov 2002 02:12:25 GMT
Organization: AT&T Broadband
Date: Thu, 28 Nov 2002 02:12:25 GMT
"Phil Hobbs" wrote in message
> Rene Tschaggelar wrote:
> > What kind of frequency range and what kind of signal range
> > are you looking at ?
> > There are 90+something dB logamps that go to 500MHz,
> > and the latest part I've seen does 160dB range up too 15MHz.
> 160 dB in 15 MHz? I don't think so. Just the thermal noise in 15 MHz
> -174 dBm+10*log(15e6)= -102 dBm. Getting a 160 dB dynamic range would
> require a maximum signal level of 600W, assuming a 300K noise
> What parts are these, exactly?
> Phil Hobbs
That sounds like the AD8304. That is a monolithic transdiode type
logarithmic amplifier. They are intended for conditioning photodiode
outputs. they do have 8 orders of magnitude of input current (100pA to
10mA) and at the high end the bandwidth is in the MHz region but the
bandwidth drops off proportionally to the input current - at 100pA it is
pretty low - in the Khz region. Obviously there is a lot of noise. You
need to filter the response to hundreds of Hz to get good reasonable
response at low current.
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