[sdiy] Eurorack Grounding Question

[Michael E Caloroso]

My first job out of college was designing test programs and test
fixtures for automated test equipment.

There was a stash of memory components that had failed test.  The
original engineer could never resolve those failures.

When I examined the test fixture, I modified it by moving the bypass
cap as close as possible to the device.  It was about a one centimeter
move.

That cured the problem, and all the "failed" components now passed.
The original engineer had trouble accepting that solution.  The
program managers were more than happy to deliver those components
regardless of his reservations.  These were for the military and I
never heard any customer complaints.

My very first ATE assignment with that group was to design a test
fixture for a buffer with a 1000V/us slew rate (NS LH0033).  The ATE
couldn't generate a step that fast so I had to build a step generator
on the fixture.  Wound up using a ComLinear CLC205 in comparator mode,
still have one.

MC

On 1/2/21, mark verbos <markverbos at gmail.com> wrote:
> Fun stuff. Reminds me of the PCB routing nightmare that I just went through
> with a small DC-DC switching power supply I made. I used TI Webbench Power
> Architect and found that some of the capacitors had to be moved directly
> onto the pins (of TSSOP ICs!)  of the ICs for the rail to start up. I
> redesigned the PCB with the parts moved to right next to the pins and found
> that the 1 or 2mm away from being on the actual pins made the same problem!
> Mind you, these are just caps from the power line to ground, but certain
> pins need them to be very close. Of course, once  the problem is found and a
> solution found, it seems obvious, but when searching for it...
>
> Mark
>
>> On Dec 31, 2020, at 11:48 AM, Ben Stuyts <ben at stuyts.nl> wrote:
>>
>> Here are a couple of good app notes if you want to read up on it:
>>
>> Grounding in mixed-signal systems demystified pt 1 & 2:
>> https://www.ti.com/lit/an/slyt499/slyt499.pdf
>> <https://www.ti.com/lit/an/slyt499/slyt499.pdf>
>> https://www.ti.com/lit/an/slyt512/slyt512.pdf
>> <https://www.ti.com/lit/an/slyt512/slyt512.pdf>
>>
>> PCB Design Guidelines For Reduced EMI:
>> https://www.ti.com/lit/an/szza009/szza009.pdf
>> <https://www.ti.com/lit/an/szza009/szza009.pdf>
>>
>> Ben
>>
>>
>>> On 31 Dec 2020, at 09:01, Steven Cook via Synth-diy
>>> <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>>>
>>> Thank you for these answers. I think I'll go with Tony's recommendation.
>>> The reason I have input jacks connected to the digital ground is simply
>>> that they are connected to the microcontroller (via transistors and
>>> reverse voltage protection diodes), so I assumed that the jacks should be
>>> also - I'll change that.
>>>
>>> I have a couple of follow-up questions:
>>>
>>> 1. If I have a ground fill on the PCBs, which ground should it be
>>> connected to?
>>>
>>> 2. Which ground should the DAC be connected to?
>>>
>>> ------ Original Message ------
>>> From: "Steven Cook via Synth-diy" <synth-diy at synth-diy.org
>>> <mailto:synth-diy at synth-diy.org>>
>>> To: Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>>> Sent: 29/12/2020 09:30:46
>>> Subject: [sdiy] Eurorack Grounding Question
>>>
>>>> Hi, I'm designing a Eurorack module which uses a microcontroller. The
>>>> PCB has separate analogue and digital grounds joined at the power input
>>>> header, but I've realised since designing it that both grounds will also
>>>> be shorted together by the front panel as there are input jacks
>>>> connected to the digital ground and output jacks connected to the
>>>> analogue ground. I assume this would create an ground loop. Would I be
>>>> better off not bothering with separate grounds?
>>>>
>>>> Regards,
>>>>
>>>> Steven Cook
>>>>
>>>>
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>>>
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>
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