Prev: Hey Tim, a unity gain 12 to 330 V DC converter :-)
Next: Retard Mike is a kook group interloper into sed.
From: Jim Thompson on 14 Jul 2010 20:49
On Wed, 14 Jul 2010 11:13:09 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>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
>

AC couple thru a DC restorer, as I've shown here recently.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama isn't going to raise your taxes...it's Bush' fault: Not re-
newing the Bush tax cuts will increase the bottom tier rate by 50%
From: Joost on 15 Jul 2010 05:42
>On Wed, 14 Jul 2010 11:13:09 -0700, John Larkin
><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
>>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
>>
>
>AC couple thru a DC restorer, as I've shown here recently.
>
To answer a few questions.
- Why did I use an OPA847?
Basically, because it was avaiable. I started out with a (good old) LF157,
and that didn't work.

- Put a shroud around it
It is installed in a small metal case, without the right case, it doesn't
work...

- If you have a lot of light then noise isn't a big problem
The pulses are coming from a 20-100W IR pulse laser with optics to focus
the beam better.
When I connect the SFA205F photo diode directly to my scope, using a 9V
battery for reverse biassing the signal is even visable.

- High ambiant?
This is used outdoors mostly in (bright) daylight

I cannot make the pulses longer, so the amplifier has to work good at
10-40MHz
It is all about isolating these 20-80ns pulses from the ambiant light,
amplifying it and turn it into a TTL level pulse.
I was thinking of turning the feedback resistor in so sort of LR filter, to
filter out the frequencies.
Mayby a voltage amplifier is a good idea, and couple it AC.

---------------------------------------
Posted through http://www.Electronics-Related.com
From: Nemo on 16 Jul 2010 10:04
Joost mentioned:

>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....)

<Strong sense of deja vu> I inherited a similar sounding circuit once. I
believe the designer used an OPA847 because on paper, it has very low
voltage noise. However, it was always right on the edge of stability. By
simply changing the amp to a Texas OPA656, the circuit became very
stable indeed, with no apparent increase in noise. I think the relevant
characteristics were:
OPA656 - bandwidth around 230MHz; OPA847 - 1.6GHz
OPA656 - much lower Cin, so easier to make stable
OPA656 - JFET input so low current noise. OPA847 - low voltage noise but
relatively high current noise, which was probably more relevant IIRC.

As someone mentioned, the ADA4817-1 is good too, it is like the OPA656
except in some characteristics where it is better. Its pinout is sort of
compatible with the standard one used by the OPA656, so with some
careful layout you can have a dual-sourced IC.

Don't use the OPA657. Looks good on paper (higher bandwidth) but has
higher Cin than its sibling the OPA656, so doesn't usually work any
better, and is trickier to stabilise.

>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.

Does 'low frequency light' mean the colour (infrared, etc) or doe sit
means pulse trains below say 10kHz? The former problem is usually solved
by using filters over the photodiode (you can get cheap bad ones for
tens of cents). The latter would be solved by adding a high pass filter
to the output of the preamp.
--
Nemo
From: George Herold on 16 Jul 2010 16:10
On Jul 15, 5:42 am, "Joost"
<joostrui(a)n_o_s_p_a_m.n_o_s_p_a_m.euronet.nl> wrote:
> >On Wed, 14 Jul 2010 11:13:09 -0700, John Larkin
> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>
> >>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
>
> >AC couple thru a DC restorer, as I've shown here recently.
>
> To answer a few questions.
> - Why did I use an OPA847?
> Basically, because it was avaiable. I started out with a (good old) LF157,
> and that didn't work.
>
> - Put a shroud around it
> It is installed in a small metal case, without the right case, it doesn't
> work...
>
> - If you have a lot of light then noise isn't a big problem
> The pulses are coming from a 20-100W IR pulse laser with optics to focus
> the beam better.
> When I connect the SFA205F photo diode directly to my scope, using a 9V
> battery for reverse biassing the signal is even visable.

With the 'scope set for 50 ohm input? You can always try just a
resistor to ground and a voltage amplifer after that. There is a
trick with a "T-coil" that can gain you a factor of two or four (?) in
bandwidth. Phil H. talks about it in his book. I've always wanted to
try it. Have you read Phil's book? There might even be a link on his
web site to the T-coil idea.

George H.
>
> - High ambiant?
> This is used outdoors mostly in (bright) daylight
>
> I cannot make the pulses longer, so the amplifier has to work good at
> 10-40MHz
> It is all about isolating these 20-80ns pulses from the ambiant light,
> amplifying it and turn it into a TTL level pulse.
> I was thinking of turning the feedback resistor in so sort of LR filter, to
> filter out the frequencies.
> Mayby a voltage amplifier is a good idea, and couple it AC.        
>
> ---------------------------------------        
> Posted throughhttp://www.Electronics-Related.com- Hide quoted text -
>
> - Show quoted text -

From: John Larkin on 16 Jul 2010 16:47
On Fri, 16 Jul 2010 13:10:22 -0700 (PDT), George Herold
<gherold(a)teachspin.com> wrote:

>On Jul 15, 5:42�am, "Joost"
><joostrui(a)n_o_s_p_a_m.n_o_s_p_a_m.euronet.nl> wrote:
>> >On Wed, 14 Jul 2010 11:13:09 -0700, John Larkin
>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>>
>> >>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
>>
>> >AC couple thru a DC restorer, as I've shown here recently.
>>
>> To answer a few questions.
>> - Why did I use an OPA847?
>> Basically, because it was avaiable. I started out with a (good old) LF157,
>> and that didn't work.
>>
>> - Put a shroud around it
>> It is installed in a small metal case, without the right case, it doesn't
>> work...
>>
>> - If you have a lot of light then noise isn't a big problem
>> The pulses are coming from a 20-100W IR pulse laser with optics to focus
>> the beam better.
>> When I connect the SFA205F photo diode directly to my scope, using a 9V
>> battery for reverse biassing the signal is even visable.
>
>With the 'scope set for 50 ohm input? You can always try just a
>resistor to ground and a voltage amplifer after that. There is a
>trick with a "T-coil" that can gain you a factor of two or four (?) in
>bandwidth. Phil H. talks about it in his book. I've always wanted to
>try it. Have you read Phil's book? There might even be a link on his
>web site to the T-coil idea.


We sometimes do the simpler version: V+, pin PD, resistor+series
inductor to ground. Then a fast voltage amp off the PD:resistor
junction. Now you can use an outrageously fast, like 2 GHz, amplifier
and not worry about TIA type issues. The inductor peaks things up a
bit. The resistor noise is now in your face, so that's the price of
simplicity.

I guess you could dump a PIN diode directly into a darlington-type
MMIC amplifier input. That sort of makes a fast, stable TIA for free.
The DC performance would be terrible, but you could sense the current
into the other end of the pin diode and use that to correct.

I suppose you could use the high-speed current signal off *both* ends
of a photodiode, into dual TIAs or MMICs, and subtract their outputs.
That halfway fixes the DC error of the MMICs, too. Gotta try that one
day.

The next step would be...

John


First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: Hey Tim, a unity gain 12 to 330 V DC converter :-)
Next: Retard Mike is a kook group interloper into sed.