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[DPRG] Working with very small voltage margins & a op amp question

Subject: [DPRG] Working with very small voltage margins & a op amp question
From: Ray Xu rayxu123 at gmail.com
Date: Thu Aug 20 15:33:54 CDT 2009

Thank you Rick,

Is it OK if I build the prototype on breadboard first, then transfer it to a
PCB?

And I'm just wondering, heck is it really possible to have noise levels
below +/- 10mV on voltages by using those techniques?

Also, I just had an idea...  I remember ECL and LVDSlogic levels use
differential signaling to avoid noise problems since they are low voltage.
I'm wondering if this would significantly reduce noise by adding a signal
splitter (VCC=+11V, virtual ground=+5.5V), then subtract each other (there
for canceling out noise) using a differential op amp configuration
(VCC=+11V, reference=GND).  Something like this:
http://en.wikipedia.org/wiki/Differential_signaling  Since I don't want to
"differentialize" my entire voltage reference circuit, I can only add this
to the output of the voltage reference generator circuit.  Would this be a
good idea to do?

Thanks

Ray Xu

On Thu, Aug 20, 2009 at 2:03 PM, Rick Bickle <rbickle at intconsys.com> wrote:

>  Ray,
>
>
>
> Use the large capacitors and inductors on the power supply rails and not on
> the signal to the laser circuitry.
>
> Use a linear power supply instead of a switching power supply. Add some
> filtering on the AC side. (i.e. balun or chokes)
>
> Keep the wires or PCB tracks short between the filtered supply and the
> op-amps.
>
> Keep all associated op-amp components as close to the chip as possible.
>
> For a PCB, put a ground plane underneath the op-amp chips and associated
> components. Tie all component grounds to the plane locally.
>
> For a prototype, use a solid copper board with the copper as a ground
> plane. Solder the chip grounds directly to it as well as all component
> grounds.
>
> Be sure to bypass all high speed switching devices with small monolithic
> capacitors close to each device.
>
> For really sensitive circuits, you can put a faraday shield (i.e. metal
> housing) around the op-amp section.
>
>
>
> Not sure I understand how the op-amps are going to set the current of your
> diode, but there are op-amps available with high current open collector
> outputs. These will give a very linear response.
>
> I recommend the book “IC Op-Amp Cookbook” by Walter Jung, available from
> Amazon. – and of course the bible “The art of Electronics” by Horowitz and
> Hill.
>
>
>
> Good Luck,
>
>
>
> Rick
>
>
>
>
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