AnsweredAssumed Answered

Cascaded stages noise calc.

Question asked by lidar on Aug 6, 2012
Latest reply on Aug 7, 2012 by lidar

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?

 

OR

 

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.

 

Thanks,

Ian

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