John Larkin a écrit :
OK, simplest case first, an emitter follower:
+10
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c
+5----------------b
e
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1K metal film
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GND
Does Ib or Ic have full shot noise? Ie sure doesn't.
Actually that's pretty easy to check with an LF SA (1M input)
15V >---.
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.-.
Rc | |
| |1K
'-'
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Adjust +---||--> SA
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for Ve=5V |
___ |/
10.7V >----|___|--+-----|
| |>
Rb --- |
--- | ||
| +---||--> SA
SA <---' | ||
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.-.
Re | |
| |1K
'-'
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===
GND
For shot noise to dominate you need:
2q.I.R > 4kT or R.I > 52mV
That's easily satisfied.
Now your SA has about 10nv/rtHz noise floor so you want the measurement
to be higher.
Shot noise across R will be en^2=R^2.2q.I = 2q.R.RI
or en= sqrt(R) sqrt(2q.R_drop).
In the above test, we have 5V across each resistor.
Full shot noise should then develop:
en=sqrt(R)x1.27nV/rtHz
which is 40nv/rtHz for a full collector shot noise.
For base shot noise if you take beta=100, then you'll have 400nV/rtHz,
800nV for beta=400.