Noise in 10nA current source

George Herold 16 years ago

This is mostly for John Larkin.

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You should be able to find a PDF atthe above site.

I used only a 10Meg ohm resistor in the front end TIA circuit. There was a bit of extra noise from the current source, but certianly nothing near shot noise. There was no attempt on my part to make the current source low noise, I suspect the extra noise is from the Voltage reference from which the current source is derived. (10 Volt refernce through a 1 Gig ohm resistor)

I did notice that there was some vibrational pickup. If I banged on the box I'd get noise spikes and could see some oscillations at 300 to

500 Hz. These are leaded 1 Gig ohm resistors and it could be it was vibrating.

George H.

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Phil Hobbs 16 years ago

Interesting. If I have time this afternoon I'll wire something up and see what I get with the dynamic signal analyzer. Taxes first, unfortunately. :(

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net

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John Larkin 16 years ago

George,

Those numbers look promising for our application. I haven't done the math yet, but a quick look suggests the resistor noise is around the Johnson level.

What kind of 100M resistor did you use?

Cool. Thanks.

John

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George Herold 16 years ago

The 1G and 100 Meg resistors are from ohmite here's the digikey part number SM102F-1000M-ND

Yeah the amplifier noise is almost exactly equal to the Johnson noise from the 10M feedback resistor.

At the lower frequencies the difference between the open circuit amplifier noise and amplifier plus 10nA current source is about 1 E

-28 Amps^2/Hz. The one G resistor should have... (Checking numbers...) 1.6 E-29 A^2/Hz... so it's about 10 times greater.. I think a quiter voltage source might cure some of this.

George H.

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