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Chip for metal detector
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Doesn't seem to be a Metal Detect????
AD8302
APPLICATIONSLog Ratio Function for AC Signals
RF/IF PA Linearization
Precise RF Power Control
Remote System Monitoring and Diagnostics
Return Loss/VSWR Measurements
Family = RF Detectors
Category = RF/IF and RFID
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Very dedicated - read application notes for VLF.
AN-691: Operation of RF Detector Products at Low Frequency
http://www.analog.com/static/importe...15AN_691_0.pdf
There are some ideas how to design PVLF ( Pulse VLF)
Design a Logamp RF Pulse Detector (pdf, 338 kB)
http://www.analog.com/static/importe...LogAmpPuls.pdf
The technology is very old (7 years) never used in MD, but working in phase and amplitude detection in video signals or mobile phones.Comment
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And most probably never will be used for MD. Just practicalities...and many reasons.Originally posted by wam View Post
First of all, putting log amp in any PI detector is completely pointless ( i tried more than once), linear decay of otherwise exponential waveform will not display much about target, sort of antilog amplifier can be more useful. For VLF there are some implications too.
-Most of VLF machines have more than 60dB dynamic range, far more. Considering this is not some UWB stuff, frequency range is unnecessarily wide, must be limited anyway, and similar circuit built using common parts (opamps etc) can perform same function at required VLF frequency.
-In typical VLF two or more phase channels are processed using first (and/or) second derivative, or bandpass, to get discrimination etc, in order to work, system must be linear, at least partially, phase and amplitude simultaneously produce target response. Whit two different logarithmic amplitudes, some MCU crap must be used to normalize response, logamp chips produce absolute level indication at output. Otherwise, all VLF detectors today will be equipped whit "hard limiter" and phase comparator, making them FM machines in essence.
Song remains the same whit GND balance etc, interference problems (now you have log variable gain stage, sometimes maybe variable gain can be useful, but not this way). Observing 1:1000 or 1:10000 signal difference on spectrum analyzer screen is nice, but of little help here.
Also i believe that people at White's, Fischer ...and others are not underpaid illiterate monkeys to miss such a great opportunity. As far as i can remember (and correct me if i'm wrong) no single MD design use logarithmic amplifiers so far.
Best regard.Comment
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O well, it was long time ago when people notice that Earth is not flat...Originally posted by Tepco View PostComment
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AD8302 output samples :
Ferryt _______Iron ____Aluminum _____Coper ____Silver
ADC_GAIN - higier signal
ADC_PHASE - lower signal.
Copy from Tomasz Gumny site.Comment
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