I am looking at designing an amplifier for a phoptomultiplier tube.
I need a gain of 25 and a Fh of 300 MHz (to drive a 1GSPS 10 bit A to D with +/- 500mV input range).
Currently I'm investigating an amp consisting of 2 off cascaded AD8099 stages each with a gain of 5.
From the data sheets each stage will have a total output noise of 8.6 nV per root Hertz.
When I cascade two stages will the total noise be
1st stage noise x 2nd stage gain + 2nd stage noise, that is,
(5 x 8.6) + 8.6 = 51.6 nV per root Hertz?
Is the noise statistical in nature and so needs different treatment, like taking the RMS value of 5 x 8.6 and 8.6 to give 43.8 nV per root Hertz.