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Hot Rod Op Amp for Eric

A

Anonymous

Guest
The OPA620 looks nice! What a time we live in. Remember when op amps were blocks.
Another canidate you may want to consider is the Comlinear CLC425 (comlinear is owned by national semiconductor). I haven't tried this for PI, but do have some and may try if I get a break from work.
I have used these before for a job a few years ago, and they are fairly forgiving as far as oscillations are concerned (Need good layout). Probably not a good amplifier for beginers. They are $11.83 in unit quantities in the states from digikey. Sure you can get them cheaper from distributors.
Ultra low Noise Wideband Op Amp. The key specs are: Voltage feedback (for those who don't like current feedback). 1.7 Ghz GBW. 1.05 nv/root Hz voltage noise. 15ma supply. 350V/us slew rate. gain 10 to 1000 (min 10) . +- 5 volt operation.
Of course full power bandwidth on amps like 709 and all the others is much less than small signal bandwidth. So large voltage swings are distorted by the limited bandwidth and then the signal settles into the small signal bandwidth. Hard to get a true first order response out of something like that, eh?
JC
 
Eric,
Still remember the post about coductive metals not having a first order response, I believe because of the decay of the surface eddy currents combined with the decay of the eddy currents which have built up within the metal. Sounds right to me. Just that the amplifiers contribute to distorting this signal further, complicating the issue of discriminating (or ground balancing) based on this response.
I made it sound like the amp was what messing up the first order response. Nope already not first order.
Since these Hot Rod amps can drive into 50/75 ohm coax, wouldn't it be wise to place one near the search coil and drive 50 ohm coax up to the rest of the electronics. Terminate into 50 ohms and have a strong (current) matched signal. Otherwise the cable forms a transmission line that is not terminated correctly, with small reflections that could turn into targets, once integrated.
JC
 
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