BJT selection for noise generator
- From: Allan Herriman <allanherriman@xxxxxxxxxxx>
- Date: Sat, 29 Sep 2007 18:16:12 +1000
Hi,
I was wondering if anyone could help with the selection of the
transistor Q1 in the noise generator circuit below?
It's an NPN, used with the EB junction reverse biased to breakdown.
Noise is generated by this breakdown, and amplified by Q2.
I'm interested in knowing what transistor parameters matter here. I
guess I don't care about the Beta degradation, as it will never be
used to amplify.
The goal is to have a reliable noise output over a (say) 10 year
product life.
Alternatively, I'm interested in knowing if there are any particular
types of transistor to avoid for this application.
VCC
===
|
|
.-.
R1 | |
| |
'-'
R2 |
___ |
.---------o-----|___|--o
| | |
| | | Output
| <| o--------
| Q1 |----. |
| /| | |
--- | | |
--- | |/
| C1 '---| Q2
| |>
| |
| |
| |
=== ===
GND GND
Thanks,
Allan
.
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