[Laser] TX Circuit for high speed data.

[Chuck Hast]

On 7/1/07, F1AVYopto at aol.com <F1AVYopto at aol.com> wrote:
> >Yves,
> >Thank you for the info. I will go at it and do the  changes. The output that
> >is driving the gate is presently coming from a  74HC04. It is buffering the
> >output of a UART. I was able to get the whole  thing to switch at 10Mhz
> >nicely last night, but that was eliminating the  1K resistors.
> Chuck
> If you drive the K3PGP laser modulator from a 74HC04, the  maximum current
> you can use from this inverter is 20 mA for one  output.
> With a 5 V psu on this 74HC04, two 330 ohms in place the two 1K in the  laser
> driver will give safe limiting loads.
> 5K in place the 100K resistor seems a good and safe value to improve the
> response time.
Yves, James,
I was thinking, why not replace the IRF-510 with say a 74HC07 open drain
buffer, I do not need anywhere near the power the MOSFET is designed for.

The 6 open drain inputs are rated for 20ma each for a total of 120ma. All
I need to do is switch a maximum of about 100ma at most, most likely
nearer to 80ma. I  can parallel inputs to get the needed current handling.

The device switches in +/-6ns so it is very fast, and since I am doing
digital data I do not need to worry about linearity from one state to the
other.



-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."