One step back – The PCB needs a redesign.

Yesterday late in the night i ran a Spice Simulation of the Filters for Analog Voltage and it showed that they are not suited to block noise in the audible spectrum (10Hz-20kHz). One option to design them better is the usage of low-noise LDOs with a high input rejection to efficiently “filter” the audio supply-rails. I am thinking of a device like the LP3982.

Simulation was done using the freely-available LTSpice-Software under WINE. Fortunately the used ferrite-beads from Würth are included in its standard library.

Simulations shows that the filter is just blocking Signals well over 100kHz – all the audible noise will pass this filter rather unimpressed. Also tweaking the L is not really helpful.


Summing up all the issues on the PCB – I decided to run a redesign of the PCB now – before we start the production of the 10pcs. batch. I think this is the smarter way to do it. Because i don’t know what will happen after the first 10pcs. are produced – The thought is something like that: If we don’t do it know, we probably will never do the redesign …

 

 

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5 responses to “One step back – The PCB needs a redesign.

  1. better safe than sorry!
    i used the ferrite-beads in my diploma thesis project for decoupling of the different ground planes. did a good job, although it was not that easy to get them (or at least 10 samples)…

  2. Note that vs1063 has very good AVDD rejection, so don’t over-design just because you think you could have a more stable AVDD. The most important thing is the RCAP capacitor connection, use no via’s.

    If you need stable AVDD for microphone bias, then that’s another thing.

  3. that is a really valuable thought – as I am kind of Analog Audiodesign newbie – I sometimes tend to overcomplicate things …
    thanks a1bert

  4. If you haven’t already, read http://www.vlsi.fi/uploads/media/vs10xxan_layout.pdf for generic and vs10xx-specific layout instructions.

    • I haven’t read it till now – I wrote down that the RCAP-C needs to be placed according to the guidelines. Also the GroundPlane on the TOP-Side is a bit messed up – we will see which changes are possible – without starting over. thanks

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