preamp noise

[KingJL]

...The MPP integrator is somewhat more quiet (1000 fold fold improvement in stop band). The GS IV is better yet with over a 3 fold improvement in stop band over the MPP (3000 fold improvement over the HH)...

Just a slight overstatement... let me pull my head out... the MPP has a 10 fold stop band improvement over the HH and the GS IV has a 30 fold stop band improvement over the HH. Still significant!!

[Carl-NC]

I did noise calculations for the Fisher pinpointer all the way through the demod to the ADC. Yep, demods are tricky.

Back at Analog Devices I started writing a document on noise calculations, originally on graph paper. I'm sure I posted scans of the graph paper version on Geotech many years ago. Since then, I've redone the whole thing in FrameMaker and added to it quite a bit. One day I need to finish it.

[Carl-NC]

Back at Analog Devices I started writing a document on noise calculations, originally on graph paper. I'm sure I posted scans of the graph paper version on Geotech many years ago. Since then, I've redone the whole thing in FrameMaker and added to it quite a bit. One day I need to finish it.

Dug it out, I had started writing several new sections on diffpair calcs, MOSFETs, flicker, and even demods. None of that was finished, so I cleaned it up and here's where it's at:

noise.pdf

I think the original was 4 pages, so it's grown a bit. It leans a bit more toward IC design and high-speed stuff, which is what I used to do. But it's still useful for metal detectors. Lemme know if I made any mistakes.

[waltr]

Great paper on noise Carl. Thanks for posting.

[green]

I have the same preamp circuit in my viscosity meter, even to using a 5532. The only difference is that I have a total gain of x470 and I roll off the response >200kHz with a small capacitor across each feedback resistor. Tomorrow I will short the input to ground and measure the peak to peak output noise. My understanding is that much of the IC noise that affects a PI RX circuit, is that which occurs below the 1kHz which is specified as 5nV rt.Hz. At 10Hz it is 16nV rt.Hz.according to the Texas data sheet. There are wide band IC's that are much lower e.g the LT1028 with 1nV rt.Hz at 10Hz, as in the data sheet in KingJL's post.

Eric.

Have you measured p-p noise at amplifier out with input to ground? I would be interested in a scope picture of integrator out with amplifier input to ground also. No target, looking for integrated noise, maybe 200 or 500ms/div.

Great paper on noise Carl. Thanks for posting. agree