🚀 go-pugleaf

> The power planes on 4 layers boards are more useful for high switching
> current and high speed digital stuff. There is a good chance it may
> make little or no difference for application depending on your layout.
> 4 layers will give you greater ability to achieve a lower noise layout,
> but if you don't know exactly how to achieve this then it's not going
> to help you much, it could even make things worse, I have seen that
> happen before.
>
To start off, I will read you tutorial from pcb123 and hopefully
improve a few things in my design from that manual. I want to add the
power layers to reduce the length of power traces (I might need to add
the 2nd stage to the detector, and that will definitely require
more/longer power traces without power layers).
>
> Simply ask the manufacturer to do it, do waste time and effort
> yourself. Just supply them the layout for one board and tell them you
> want X number of boards. For the prototype services they will usually
> fit as many as they can on the one panel for you, you pay per panel.
>
> For high production designs it's usually different, you have to worry
> about panel handling and tooling hole/marks etc.
>
Any recommendations, I'm using pcbexpress, will try to get a hold of
them after New Year's day, local manufacturers are charging per panel
(but I will see if they can put a few designs on the same panel).

John Devereux wrote:
>
> These requirements tend to be mutually exclusive... i.e., more
> bandwidth lets in more noise.
>
> What is the source of the "noise"? E.g. source noise, photocurrent
> shot noise, transimpedance amplifier noise, external interference?
>
> Until you do this it seems pointless to speculate about numbers of
> layers in boards.
>
> John Devereux
What I meant was: I must increase the BW but see if there is a way to
reduce the noise (it does not have to be less than what I have right
now).
I was thinking differently: if I can provide more stable voltage to
both opamp and photodiodes, I can get less fluctuations during current
generation and amplifications and power plane should give more stable
voltage, right? (I can be totally wrong about this)

John Larkin wrote:
> More layers won't necessarily improve speed or reduce noise. If you
> increase trace capacitance (from thinner dielectrics) it might make
> things worse.
>
> 10 or even 40 MHz isn't very fast for a photodetector; I've got 180
> MHz from cheap opamps. What detector device are you using? Increasing
> the photodiode back-bias should help speed a bunch, maybe 2:1 if you
> go from 5 volts to something like 20.
>
> What's the application? How much noise do you see, in equivalent
> optical power?
>
> John
I'm using InGaAs PIN (Small Area/Fiber-Optic) photodiodes, which
according to the datasheet should be biased at 5V, wavelenth of the
signals varies between 800nm to 1700nm. NEP of the photodiode is <0.02
pW/sqrt(Hz) @1550nm according to the datasheet.


Vitaliy