R
[email protected]
- Jan 1, 1970
- 0
Hello,
I need to build a white noise source from 1 Hz to 100 kHz (the more the
better)
and came across a photodiode shot noise source which seems fine because
it can
be calculated and I don't have the facilities to calibrate a zener
noise source.
Message from Phil Hobbs
http://groups.google.com/group/[email protected]
Now I need a concrete design idea:
a) use an inverting amplifier with a big feedback resistor (1 G)
Illuminate the diode for 1 nA Photocurrent.
This gives me 1.8e-14 A/sqrt(Hz) current noise,
with 10 KHz bandwidth 1.8 mV after the amplifier.
LF411 has around 10 fA/sqrt(Hz) noise, this is not negligible with
respect to the shot noise.
In addition, johnson noise from the feedback resistor is to large,
since
the voltage is below 50 mV (2kT/e)
b) use 1 mA photocurrent and see how to get rid of the DC before
amplification.
Use the active load circuit from Zetex application note AN3, figure 6.
------|------- +Vee
|1k5 |
..-. |33n
| | ---
| | --- ___
'-' | ||___||
| | | |
| | 330k | |
/| | | >------||-
| | GND-|+/ ||
|-------------- |/| out
-
^
|photodiode
|
|
------------ -Vcc
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Probably I would use a current source to sink the current from the
photodiode
and use negative feedback from the output of the OPA to the light
source to have
a better response at low frequencies
Do you have any comments?
Many thanks for your feedback
Daniel
I need to build a white noise source from 1 Hz to 100 kHz (the more the
better)
and came across a photodiode shot noise source which seems fine because
it can
be calculated and I don't have the facilities to calibrate a zener
noise source.
Message from Phil Hobbs
http://groups.google.com/group/[email protected]
Now I need a concrete design idea:
a) use an inverting amplifier with a big feedback resistor (1 G)
Illuminate the diode for 1 nA Photocurrent.
This gives me 1.8e-14 A/sqrt(Hz) current noise,
with 10 KHz bandwidth 1.8 mV after the amplifier.
LF411 has around 10 fA/sqrt(Hz) noise, this is not negligible with
respect to the shot noise.
In addition, johnson noise from the feedback resistor is to large,
since
the voltage is below 50 mV (2kT/e)
b) use 1 mA photocurrent and see how to get rid of the DC before
amplification.
Use the active load circuit from Zetex application note AN3, figure 6.
------|------- +Vee
|1k5 |
..-. |33n
| | ---
| | --- ___
'-' | ||___||
| | | |
| | 330k | |
|---|-|___|--------------|-\ | ||| | ___ ||\| |
/| | | >------||-
| | GND-|+/ ||
|-------------- |/| out
-
^
|photodiode
|
|
------------ -Vcc
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Probably I would use a current source to sink the current from the
photodiode
and use negative feedback from the output of the OPA to the light
source to have
a better response at low frequencies
Do you have any comments?
Many thanks for your feedback
Daniel