Go Down

Topic: Photo Diode - Amplifier (Read 3 times) previous topic - next topic

jremington

#15
Feb 05, 2014, 10:12 pm Last Edit: Feb 05, 2014, 10:37 pm by jremington Reason: 1
Nice work, pito! I take it you live on Easter Island.
Having visited there for a couple of weeks some 20 years ago, I imagine that you feel a bit isolated (in terms of technical interests).

Regarding the topic, I'm wondering if the preamp can be dispensed with and a fast comparator with positive feedback (to introduce hysteresis) coupled directly with the photodiode could be used. I will try some design simulations along those lines. Incidentally, the BPW34 PIN diode has 25 pF capacitance at 3V reverse bias, so your simulations were spot on.
"It seems to run on some form of electricity"

pito

#16
Feb 06, 2014, 01:49 pm Last Edit: Feb 06, 2014, 02:05 pm by pito Reason: 1
Quote
Incidentally, the BPW34 PIN diode has 25 pF capacitance at 3V reverse bias, so your simulations were spot on.

With the above schematics the Vr would be 8.45V - at that voltage (based on the datasheet) is the cap ~17pF.
Add 3pF stray.
So 2 diodes in parallel would require 30V to see the same shape.
The major issue with above schematics is the setting the comparator level is critical. Not feasible in real design. I cannot recommend that. You would never be able to set it properly. Another approach needs to be taken.

pito

#17
Feb 06, 2014, 03:19 pm Last Edit: Feb 06, 2014, 03:36 pm by pito Reason: 1
This gives nice output from 1nA - 500nA diode pulses.. (inp. noise not considered). Diode pulse: 20ns duration and 20ns rising/falling edges. Parts used are an example only. Use the best one you can get :)
No warranties of any kind, provided as-is..

Greenality

@pito
Hi,
thank you so much, you really really saved my day.  :-)
Thanks a lot, this is very helpful to me, thank you for taking the time to answer my questions. Thanks a lot. :-)

King regards,

Greenality

jremington

Hamamatsu published some nice photodiode example circuits, which include a couple of other options for detection of X-rays or gamma rays. Two that look interesting are a lot less complex than what is being discussed, see attached photo. One circuit includes using a piece of scintillation material (available on eBay) that produces weak pulses of light from X-ray or gamma photons, which the photodiode then detects. The other circuit amplifies the weak current pulses produced by gamma rays in the photodiode itself, but the pulse output is still too low in amplitude for an Arduino to detect directly. Here is the link: http://www.hamamatsu.com/resources/pdf/ssd/si_pd_circuit_e.pdf
"It seems to run on some form of electricity"

Greenality


This gives nice output from 1nA - 500nA diode pulses.. (inp. noise not considered). Diode pulse: 20ns duration and 20ns rising/falling edges. Parts used are an example only. Use the best one you can get :)
No warranties of any kind, provided as-is..

Hi,

I have found all of these components except one, the CMD1 O.94V -IC thing. Could maybe anyone send me a link where you can buy this? It would be very nice. :-)
They things V1 and V2 are not needed in a real circuit, are they?

King regards,

Greenality

jremington

.IC specifies initial conditions for the circuit simulator. Yes, voltage sources VS1 and VS2 are required but in practise have to be constructed from components. The circuit as shown works in simulations only.
"It seems to run on some form of electricity"

Greenality

Hi,

ok when it does not work in reality is it possible that maybe someone could make a circuit for me? I have some problems with that.
I would be very happy. :-) Looking forward to hear from you. :-)

King regards,

Greenality :-)

jremington

"It seems to run on some form of electricity"

Go Up