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From: Joost on 14 Jul 2010 12:26
I am experimenting with a SI photodiode receiver using a Texas Instruments
OPA847 opamp as a transimpedance amplifier and a SFH205F photodiode. I was
able to get the amplifier stable. (at last....)

The only things I have to change is make the receiver work better in high
ambiant light conditions. At the end this receiver has to detect very short
(pulse) near IR laser flashes (around 50ns long pulses at 100Hz to 10000Hz
pulse frequencies)
I do not need the high bandwidth that the current designs has, the less
sensitive to low frequency light signals the better.

Any ideas to improve my design would be very welcome?



---------------------------------------
Posted through http://www.Electronics-Related.com
From: amdx on 14 Jul 2010 13:35

"Joost" <joostrui(a)n_o_s_p_a_m.euronet.nl> wrote in message
news:nsidnfu4KrPVeKDR4p2dnAA(a)giganews.com...
>I am experimenting with a SI photodiode receiver using a Texas Instruments
> OPA847 opamp as a transimpedance amplifier and a SFH205F photodiode. I was
> able to get the amplifier stable. (at last....)
>
> The only things I have to change is make the receiver work better in high
> ambiant light conditions. At the end this receiver has to detect very
> short
> (pulse) near IR laser flashes (around 50ns long pulses at 100Hz to 10000Hz
> pulse frequencies)
> I do not need the high bandwidth that the current designs has, the less
> sensitive to low frequency light signals the better.
>
> Any ideas to improve my design would be very welcome?

Put a shroud around it?
Mike


From: John Larkin on 14 Jul 2010 14:13
On Wed, 14 Jul 2010 11:26:48 -0500, "Joost"
<joostrui(a)n_o_s_p_a_m.euronet.nl> wrote:

>I am experimenting with a SI photodiode receiver using a Texas Instruments
>OPA847 opamp as a transimpedance amplifier and a SFH205F photodiode. I was
>able to get the amplifier stable. (at last....)
>
>The only things I have to change is make the receiver work better in high
>ambiant light conditions. At the end this receiver has to detect very short
>(pulse) near IR laser flashes (around 50ns long pulses at 100Hz to 10000Hz
>pulse frequencies)
>I do not need the high bandwidth that the current designs has, the less
>sensitive to low frequency light signals the better.
>
>Any ideas to improve my design would be very welcome?


If you have a lot of light, namely noise isn't a big problem, you
could AC couple the signal such that ambient light doesn't saturate
the opamp, or even such that the opamp doesn't see it at all.

The pin diode could drive a resistor to ground or V- (double the
bias!) with that node capacitively coupled into the TIA. Or you could
dump the pin diode current into a paralleled inductor+resistor to
ground, and then use a voltage amplifier, not a TIA. That would be
stable and probably faster.

Now Phil will tell us how to do it *right*

John


From: George Herold on 14 Jul 2010 15:52
On Jul 14, 12:26 pm, "Joost" <joostrui(a)n_o_s_p_a_m.euronet.nl> wrote:
> I am experimenting with a SI photodiode receiver using a Texas Instruments
> OPA847 opamp as a transimpedance amplifier and a SFH205F photodiode. I was
> able to get the amplifier stable. (at last....)

Why did you use that opamp? It says it stable for gains greater than
12! What is the value of your feed back resistor? You opamp also has
a lot of current noise. (3 pA/rtHz.)

There's a fast FET opamp from Analog. ADA4817 that might work
better.

>
> The only things I have to change is make the receiver work better in high
> ambiant light conditions. At the end this receiver has to detect very short
> (pulse) near IR laser flashes (around 50ns long pulses at 100Hz to 10000Hz
> pulse frequencies)
> I do not need the high bandwidth that the current designs has, the less
> sensitive to low frequency light signals the better.
>
> Any ideas to improve my design would be very welcome?

What is high ambient light? indoors or outdoors? What's the laser
power and how much current are you seeing...

Can you make the pulses longer? What is the bandwidth of the current
design. Seems like you'd like something around 20 MHz or more to
catch the 50 ns pulse.

A shroud is always a good idea as someone suggested.

George H.
>
> ---------------------------------------        
> Posted throughhttp://www.Electronics-Related.com

From: David Eather on 14 Jul 2010 19:43
On 15/07/2010 5:52 AM, George Herold wrote:
> On Jul 14, 12:26 pm, "Joost"<joostrui(a)n_o_s_p_a_m.euronet.nl> wrote:
>> I am experimenting with a SI photodiode receiver using a Texas Instruments
>> OPA847 opamp as a transimpedance amplifier and a SFH205F photodiode. I was
>> able to get the amplifier stable. (at last....)
>
> Why did you use that opamp? It says it stable for gains greater than
> 12! What is the value of your feed back resistor? You opamp also has
> a lot of current noise. (3 pA/rtHz.)
>
> There's a fast FET opamp from Analog. ADA4817 that might work
> better.
>
He doesn't need the bandwidth - he might get away with a TL071


>>
>> The only things I have to change is make the receiver work better in high
>> ambiant light conditions. At the end this receiver has to detect very short
>> (pulse) near IR laser flashes (around 50ns long pulses at 100Hz to 10000Hz
>> pulse frequencies)
>> I do not need the high bandwidth that the current designs has, the less
>> sensitive to low frequency light signals the better.
>>
>> Any ideas to improve my design would be very welcome?
>
> What is high ambient light? indoors or outdoors? What's the laser
> power and how much current are you seeing...
>
> Can you make the pulses longer? What is the bandwidth of the current
> design. Seems like you'd like something around 20 MHz or more to
> catch the 50 ns pulse.
>
> A shroud is always a good idea as someone suggested.
>
> George H.
>>
>> ---------------------------------------
>> Posted throughhttp://www.Electronics-Related.com
>

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