[BP] thermal noise question for signaling conference call today

[John Stonick <John.Stonick@xxxxxxxxxxxx>]

I am confused what the -140dBm number refers to in the discussion today (I
do not recall who put it forth).

-140dbm/Hz is equivalent to 3.2nV/sqrt(Hz).

[-140dBm/Hz = -170dBw/Hz = 1e-17W/Hz = 3.2nV/sqrt(Hz)].

You only get to 32nv/sqrt(Hz) (the number that was said to result) if you
multiply the original number by 100 (1e-17*100 W/Hz = 32nV/sqrt(Hz)) The
factor of 100 was Mike's resistor value. If this is why this was done then I
am assuming that the person who mentioned this is using the standard spot
noise equation for noise from a resistor:

Pspot = 4kTR = 1e-15 (derived from 32nV/sqrt(Hz))

4(1.38e-23)T(100) = 1e-15W/Hz

T = 181e3

This seems bizarre. Can someone explain why we multiplied -140dBm = 1e-17W
by 100? If we do not do this and use 3.2nV/sqrt(Hz) then we end up with
224uV of noise. Mike's value would have led to about 100uV of noise.

I am not sure what the proper number to include for thermal noise, but I
think that 2.2mV is a bit high.

jts

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     John T. Stonick, Ph.D.
     Scientist
     Synopsys, Inc.
     Synopsys Technology Park
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     Hillsboro, OR 97124
     (P) (503)547-6535
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