Hi all,
I am posting to this forum at the suggestion of George Herold from Teachspi n, he says you are the people to help me out. I understand a decent amount about circuits, but not enough to design the low-noise TIA I would like to build.
We're trying to create a modern version of the Tolman-Stewart experiment ht tps://en.wikipedia.org/wiki/Stewart%E2%80%93Tolman_effect that was one of t he first proofs that electrons inside metals carry the current.
In this experiment, a coil of wire is spun to high speeds and then braked r apidly. The electrons keep moving and create a small pulse of current. Or iginally, Tolman and Stewart used a ballistic galvanometer to act as a char ge amplifier and integrate the current to find the total charge.
I?d like to use a TIA to convert the small current pulse into a vol tage, then record that voltage as a function of time. The problem is that the coil acts as a giant antenna and picks up all sorts of unwanted noise, so I?d like to get rid of that noise. In particular, it is really good at finding 60 Hz signals in the room.
Right now we?re using an OPA 140 with 1 GOhm and 10 pF as a feedbac k resistor and capacitor in parallel. We attach the coil (about 200 Ohm re sistance, 500 mH inductance) to one input and put the other input across 20
0 Ohms to ground. The large amplification leads to huge amplification of t he noise, and it is hard to see our signal. We expect the current pulse to be 1 nA of current, almost square wave in shape, and it should last the du ration of the braking, about 0.5 seconds.Any suggestions appreciated!
--Matt Sullivan Ithaca College Physics