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
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
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