amplifying a photodiode signal

J

Jamie Morken

Guest
Hi,

I have a photodiode with the anode connected to a 100K pullup to 12V,
cathode to ground, and an RC highpass filter (47pF, 2.2Mohm) driven from
the photodiodes anode, what is the best way to amplify the signal to 1V
peak to peak from the highpass filter assuming a frequency of up to
500MHz at 0.1mV amplitude? I am thinking of an MMIC RF amplifier, or a
high speed comparator but I am not sure what would be best. I would
like to feed this signal into a high speed serial to parallel converter
to interface it to 5Volt logic.

cheers,
Jamie
 
Hi,

John Popelish wrote:

How much capacitance does the photo diode have?
What is the impedance of that capacitance at 500 MHz?
Click to expand...
I am not sure about the capacitance, it isn't in the 2page datasheet I have.

It is used in the Ronja optical datalink project:
http://ronja.twibright.com/main.php


400MHz 820nm photodiode
digikey part#: 425-1029-5-ND manufacturer part#: PD101SC0SS

cheers,
Jamie

I doubt you have any chance of getting a usable signal out of a 100k
pull up resistor at 500 MHz. You need a much lower load impedance
across the photo diode. I think you should look into using a
transconductance amplifier or common base amplifier at the front end
and incorporate the high pass filter into that.
Click to expand...
 
I read in sci.electronics.design that Jamie Morken <jmorken@shaw.ca>
wrote (in <BQeDd.34591$nN6.28399@edtnps84>) about 'amplifying a
photodiode signal', on Thu, 6 Jan 2005:
Hi,

I have a photodiode with the anode connected to a 100K pullup to 12V,
cathode to ground, and an RC highpass filter (47pF, 2.2Mohm) driven from
the photodiodes anode, what is the best way to amplify the signal to 1V
peak to peak from the highpass filter assuming a frequency of up to
500MHz at 0.1mV amplitude? I am thinking of an MMIC RF amplifier, or a
high speed comparator but I am not sure what would be best. I would
like to feed this signal into a high speed serial to parallel converter
to interface it to 5Volt logic.

500MHz and 2.2 Mohm are incompatible. You will not get the filtering you
Click to expand...
expect. The stray capacitance across your 100 kohm also attenuates such
fast signals severely.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
Hi, you won't get anything like 500MHz from such a simple circuit. There is
good site somewhere that tells you how to do it, I can't remember where but it
didn't take me long to find using the search engines. Your other option is to
read the diodes application notes, usually the best place to start anyway.
 
Jamie,
you need to make the diode fast by a moderate reverse voltage
of say 12V or so. What photodiode do you have and what is its
rise time ? Then how much light do you have ? And how
much jitter can you tolerate ?

Rene

Jamie Morken wrote:
Hi,

I have a photodiode with the anode connected to a 100K pullup to 12V,
cathode to ground, and an RC highpass filter (47pF, 2.2Mohm) driven from
the photodiodes anode, what is the best way to amplify the signal to 1V
peak to peak from the highpass filter assuming a frequency of up to
500MHz at 0.1mV amplitude? I am thinking of an MMIC RF amplifier, or a
high speed comparator but I am not sure what would be best. I would
like to feed this signal into a high speed serial to parallel converter
to interface it to 5Volt logic.
Click to expand...
 
Hi,

I found a good site that goes through this topic very well:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=4346&pg=1

cheers,
Jamie


Rob Gaddi wrote:
Go get yourself a copy of Jerald Graeme's book "Photodiode Amplifiers:
Op Amp Solutions" It's got lots of pretty equations that you can use
for the first stage transimpedance amp. All of the posts regarding the
fact that you won't be able to get that kind of signal swing from a
passive I/V converter are dead on the money.

That said, how much current are you expecting to be able to get from
your photodiode? Your specs as provided indicate that you're expecting
about 1 nA signal amplitude. In my experience, if you're trying to gain
up that small of a photodiode signal across that wide of a bandwidth
you're going to be lucky to get 3 bits of data above the noise floor.

Jamie Morken wrote:

Hi,

I have a photodiode with the anode connected to a 100K pullup to 12V,
cathode to ground, and an RC highpass filter (47pF, 2.2Mohm) driven
from the photodiodes anode, what is the best way to amplify the signal
to 1V peak to peak from the highpass filter assuming a frequency of up
to 500MHz at 0.1mV amplitude? I am thinking of an MMIC RF amplifier,
or a high speed comparator but I am not sure what would be best. I
would like to feed this signal into a high speed serial to parallel
converter to interface it to 5Volt logic.

cheers,
Jamie
Click to expand...
 
Yes, you can AC couple the photodiode and use an RF amplifier.
Typically, you'd use a 50Ohm load. However, photodiode will have to be
quite small to have sufficiently small capacitance for 500MHz
operation, AND, you'll have to begin by understanding that the CATHODE
is positive for reverse bias!

Paul Mathews
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top