Maker Pro
Maker Pro

Filtering ideas

Sven said:
--- snip ---




A pure inductor does not cause shot noise, but the OP-amp does.
The source impedance would shunt this shot noise, so when Z-source is
low the shot noise is not dominant.
When Z-source is high, it is!


So in this particular op-amp (LT1028), the high impedance would cause
the op-amp to create more noise? What if I use a fet op-amp that has
10^12 input resistance?

The datasheet for this chip provides a table to find the best-suited
chips verses input source resistance. This chip is best for <400 ohms
input. There are other chips listed in the table that are better for
68K ohms, but it says resistance, not reactance. Since my coil only has
22 ohms (but a lot of reactance) I thought this would be a good op-amp
choice. They mention other chips that are better for more input
resistance. Does such a table pertain to both input source resistance
and reactance?

Any recommendations? Just trying to minimize noise and understand why
the op-amps would cause such noise. It's just a little frustrating to
hear that all this inductance is not any better than resistance and
somehow causes the op-amp to be noisy even though inductance itself
doesn't cause noise.

Thanks,
Paul
 
Top