Hello, For a wide band (0.1Hz-1MHz) low impedance small signal source I need to design a room temperature ultra low noise high gain preamp.
The specs are about 50nV rms (yes!) integrated over the 1MHz band, which is
50pV/root(Hz) noise density.
Some system specificities allow me to build the preamp like this :
.-----------------. | | | 200pV/root(Hz) | IN | | --------+-----------| G=10000 |----. .----------------. | | | | | | | | | | | | | | | | | '---| LP | | | '-----------------' | | | | | | | OUT --- |----------| SUM |----- --- .-----------------. | | | | | | .---| | | | 1:4 | 200pV/root(Hz) | | | HP | | | | | | | | | '---. ,-----| |----' | | | )|( | G=10000 | '----------------' )|( | | -' '- | | | '-----------------' === GND (created by AACircuit v1.28 beta 10/06/04
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having a 200pV/rt(Hz) noise density in the low frequency region and
50pV/rt(Hz) in the high frequency region (expected crossover about 10kHz).
At this level there are lots of noise sources to chase, one being the transformer thermal noise. Windings noise will be low but core magnetics thermal noise might be a pb (magnetic domain noise).
Any experience with this phenomena?
One hour googling didn't give anything useful (like orders of magnitude, PSD shape, ...)