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From: George Herold on 16 Jul 2010 17:19
On Jul 16, 4:47 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 16 Jul 2010 13:10:22 -0700 (PDT), George Herold
>
>
>
>
>
> <gher...(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.

Yeah I think ye ole capacitance is an issue too. 10 pF can ruin your
day.

But the only way I've done any thing fast is just like that. (I never
tried an inductor) and then used a mini-circuits amp. (cheating?)

>
> 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 don't know MMIC amps. Do they sense current?

>
> 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.

Yeah I had that (or similar) idea. You've still got to reverse bias
the photodiode. Which you can do by biasing the (+) input of on of
the TIA's.. then you've got your ouputs at differernt DC levels... but
Phil H. posted some circuit to take care of the DC offset... I can't
remember what it looked like. Too many beers.
>
> The next step would be...
Sell it and design something else!

George H.
>
> John- Hide quoted text -
>
> - Show quoted text -

From: John Larkin on 16 Jul 2010 18:34
On Fri, 16 Jul 2010 14:19:51 -0700 (PDT), George Herold
<gherold(a)teachspin.com> wrote:

>On Jul 16, 4:47�pm, John Larkin
><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> On Fri, 16 Jul 2010 13:10:22 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <gher...(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.
>
>Yeah I think ye ole capacitance is an issue too. 10 pF can ruin your
>day.
>
>But the only way I've done any thing fast is just like that. (I never
>tried an inductor) and then used a mini-circuits amp. (cheating?)
>
>>
>> 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 don't know MMIC amps. Do they sense current?

I mean something like an ERA-1, which you are probably familiar with.
They are usually an InP darlington transistor with a c-b feedback
resistor, practically a TIA already. They are characterized for
wideband RF usage, with a nominal (nominal!) 50 ohm match on input and
output, and are usually unconditionally stable. They work nicely as
pulse amplifiers, but their DC stability is bad.

>
>>
>> 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.
>
>Yeah I had that (or similar) idea. You've still got to reverse bias
>the photodiode. Which you can do by biasing the (+) input of on of
>the TIA's.. then you've got your ouputs at differernt DC levels... but
>Phil H. posted some circuit to take care of the DC offset... I can't
>remember what it looked like. Too many beers.

Sorry, I can't understand those words "too many beers."

I was cooking and I asked my wife (who is half Italian) whether I was
using too much garlic. She replied "Sorry, I can't understand those
words..."


>>
>> The next step would be...
>Sell it and design something else!

Actually, I had a really cool idea for the next step. But I forgot it.

John

From: George Herold on 17 Jul 2010 11:13
On Jul 16, 6:34 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 16 Jul 2010 14:19:51 -0700 (PDT), George Herold
>
>
>
>
>
> <gher...(a)teachspin.com> wrote:
> >On Jul 16, 4:47 pm, John Larkin
> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> On Fri, 16 Jul 2010 13:10:22 -0700 (PDT), George Herold
>
> >> <gher...(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.
>
> >Yeah I think ye ole capacitance is an issue too.  10 pF can ruin your
> >day.
>
> >But the only way I've done any thing fast is just like that.  (I never
> >tried an inductor)   and then used a mini-circuits amp. (cheating?)
>
> >> 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 don't know MMIC amps.  Do they sense current?
>
> I mean something like an ERA-1, which you are probably familiar with.
> They are usually an InP darlington transistor with a c-b feedback
> resistor, practically a TIA already. They are characterized for
> wideband RF usage, with a nominal (nominal!) 50 ohm match on input and
> output, and are usually unconditionally stable. They work nicely as
> pulse amplifiers, but their DC stability is bad.

ERA-1, I don't know it at all, but I've got goggle.
I've only been doing 'real'* electronics for 10 years...(Wow it
doesn't seem that long.) And most of that is mucking about at or near
DC.


*'real' meaning someone is buying what I make.
>
>
>
> >> 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.
>
> >Yeah I had that (or similar) idea.   You've still got to reverse bias
> >the photodiode.  Which you can do by biasing the (+) input of on of
> >the TIA's.. then you've got your ouputs at differernt DC levels... but
> >Phil H. posted some circuit to take care of the DC offset... I can't
> >remember what it looked like.  Too many beers.
>
> Sorry, I can't understand those words "too many beers."
>
> I was cooking and I asked my wife (who is half Italian) whether I was
> using too much garlic. She replied "Sorry, I can't understand those
> words..."

Hah, Yup never to much garlic or onions! All my favorite dishes start
by carmalizing as many vadalhas(sp) as I can fit in my frying pan.

>
>
>
> >> The next step would be...
> >Sell it and design something else!
>
> Actually, I had a really cool idea for the next step. But I forgot it.

Oh, I was thinking that instead of adding the two signals you could
amplify and then multiply.
The amplifier noise should go down by a factor of two. (And more if
you averaged.) I think my new Rigol DSO has a multiply function.

George H.

>
> John- Hide quoted text -
>
> - Show quoted text -

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