Digitial and Analog line drivers for laser control

[Kurt Thorn]

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Hi All -

A problem I've run into a few times now is that we have a digital or
analog I/O board with relatively high impedance outputs that we want to
use to drive a laser with 50 ohm inputs. I've encountered this for both
digital and analog control.  I'd like to be able to buy a line driver
(digital or analog) that I can put in between the I/O board and the
laser fix the impedance mismatch.  Does anyone know of a source for such
a thing? I could build one myself, but I'd rather not if I don't have to.

Kurt

--
Kurt Thorn
Director, Nikon Imaging Center
http://nic.ucsf.edu/blog/

[Craig Brideau]

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An emitter-follower circuit should do the trick, depending on how quickly
you modulate the laser.

Craig



On Mon, Feb 24, 2014 at 4:10 PM, Kurt Thorn <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hi All -
>
> A problem I've run into a few times now is that we have a digital or
> analog I/O board with relatively high impedance outputs that we want to use
> to drive a laser with 50 ohm inputs. I've encountered this for both digital
> and analog control.  I'd like to be able to buy a line driver (digital or
> analog) that I can put in between the I/O board and the laser fix the
> impedance mismatch.  Does anyone know of a source for such a thing? I could
> build one myself, but I'd rather not if I don't have to.
>
> Kurt
>
> --
> Kurt Thorn
> Director, Nikon Imaging Center
> http://nic.ucsf.edu/blog/
>

[Craig Brideau]

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Here's a calculator:

http://www.ece.umd.edu/~neil/306/ckts/ef.htm

And a little tutorial:

http://www.eecs.tufts.edu/~dsculley/tutorial/transistors/transistors2.html

Note they are also known as common collector circuits.  Basically it
isolates one section of a circuit from another.  Pretty handy!

Craig



On Mon, Feb 24, 2014 at 4:34 PM, Craig Brideau <[hidden email]>wrote:

> An emitter-follower circuit should do the trick, depending on how quickly
> you modulate the laser.
>
> Craig
>
>
>
> On Mon, Feb 24, 2014 at 4:10 PM, Kurt Thorn <[hidden email]> wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>> *****
>>
>> Hi All -
>>
>> A problem I've run into a few times now is that we have a digital or
>> analog I/O board with relatively high impedance outputs that we want to use
>> to drive a laser with 50 ohm inputs. I've encountered this for both digital
>> and analog control.  I'd like to be able to buy a line driver (digital or
>> analog) that I can put in between the I/O board and the laser fix the
>> impedance mismatch.  Does anyone know of a source for such a thing? I could
>> build one myself, but I'd rather not if I don't have to.
>>
>> Kurt
>>
>> --
>> Kurt Thorn
>> Director, Nikon Imaging Center
>> http://nic.ucsf.edu/blog/
>>
>
>

[Mark Cannell-2]

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Yes, but remember the one diode drop difference (Vbe) between input and output (not a problem for digital). For digital such things are known as line drivers and you can get 4 (or more) in one package. For analog, something like an AD811 should do. I don’t know of a ready built solution for this interface problem,  if you can’t make the circuit, there are other computer interface boards that will drive 50 ohm loads that may provide a simpler solution for you…

HTH

Mark

>
>
>
> On Mon, Feb 24, 2014 at 4:34 PM, Craig Brideau <[hidden email]>wrote:
>
>> An emitter-follower circuit should do the trick, depending on how quickly
>> you modulate the laser.
>>
>> Craig
>>
>>
>>
>> On Mon, Feb 24, 2014 at 4:10 PM, Kurt Thorn <[hidden email]> wrote:
>>
>>> *****
>>> To join, leave or search the confocal microscopy listserv, go to:
>>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
>>> *****
>>>
>>> Hi All -
>>>
>>> A problem I've run into a few times now is that we have a digital or
>>> analog I/O board with relatively high impedance outputs that we want to use
>>> to drive a laser with 50 ohm inputs. I've encountered this for both digital
>>> and analog control.  I'd like to be able to buy a line driver (digital or
>>> analog) that I can put in between the I/O board and the laser fix the
>>> impedance mismatch.  Does anyone know of a source for such a thing? I could
>>> build one myself, but I'd rather not if I don't have to.
>>>
>>> Kurt
>>>
>>> --
>>> Kurt Thorn
>>> Director, Nikon Imaging Center
>>> http://nic.ucsf.edu/blog/
>>>
>>
>>

Mark  B. Cannell Ph.D. FRSNZ
Professor of Cardiac Cell Biology
School of Physiology &  Pharmacology
Medical Sciences Building
University of Bristol
Bristol
BS8 1TD UK

[hidden email]

[Andrew York]

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I've run into this problem myself, and was surprised I couldn't find a
simple premade buffer amplifier for sale. I ended up building my own with
radio shack parts, but it's annoying for sure.

Some NI boards can drive low impedance loads, I think the 6733 works. Some
are spec'd to do this, but fail. I'm interested in a good approach to this
problem too, if anyone can help.
On Feb 24, 2014 6:11 PM, "Kurt Thorn" <[hidden email]> wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Hi All -
>
> A problem I've run into a few times now is that we have a digital or
> analog I/O board with relatively high impedance outputs that we want to use
> to drive a laser with 50 ohm inputs. I've encountered this for both digital
> and analog control.  I'd like to be able to buy a line driver (digital or
> analog) that I can put in between the I/O board and the laser fix the
> impedance mismatch.  Does anyone know of a source for such a thing? I could
> build one myself, but I'd rather not if I don't have to.
>
> Kurt
>
> --
> Kurt Thorn
> Director, Nikon Imaging Center
> http://nic.ucsf.edu/blog/
>

[Zdenek Svindrych]

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Hi Kurt,



have you checked the specs of your I/O board? High impedance analog outputs
are rare on good quality lab equipment and high impedance digital outputs
are a mere nonsense. It is possible that your board uses 3.3V interface,
this is common on modern cheapo hardware. You cancheck this with an
oscilloscope (or voltmeter) andsome dummy load.




Just check whether there are some hardware jumpers or software settings that
could swithch the outputs to low impedance.




The same may apply for your laser. High impedance (about 1 kOhm) is more
common, the 50 Ohm is an option that might be "deactivated". Again look into
some detailed manual.




It is simple to build a level converter or a buffer yourself. I couldn't
find any simple ready solution for you on the net... Most of the results
(both devices and schematics) I could find are impedance converters for very
high frequencies, that's an overkill.




Good luck!




zdenek svindrych

1st faculty of medicine, cuni.cz



---------- Původní zpráva ----------
Od: Kurt Thorn <[hidden email]>
Komu: [hidden email]
Datum: 25. 2. 2014 0:11:12
Předmět: Digitial and Analog line drivers for laser control

"*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Hi All -

A problem I've run into a few times now is that we have a digital or
analog I/O board with relatively high impedance outputs that we want to
use to drive a laser with 50 ohm inputs. I've encountered this for both
digital and analog control. I'd like to be able to buy a line driver
(digital or analog) that I can put in between the I/O board and the
laser fix the impedance mismatch. Does anyone know of a source for such
a thing? I could build one myself, but I'd rather not if I don't have to.

Kurt

--
Kurt Thorn
Director, Nikon Imaging Center
http://nic.ucsf.edu/blog/"