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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
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Old 8th January 2019, 02:35 AM   #11
Ken Newton is offline Ken Newton  United States
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Attached, is an Analog Devices App. Note on this very subject.
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File Type: pdf MT-031.pdf (144.7 KB, 37 views)
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Old 8th January 2019, 04:48 AM   #12
ygg-it is offline ygg-it  Italy
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"Separate analog and digital ground planes should be used... The two ground planes must of course be connected together by a single junction close to the IC. "

So, this seems to be supported by the majority of DIY hobbysts.

Professional manufacturers seems to be in partial disagreement, as it looks that the DAC chip should be connected exclusively to the Analog ground plane.

See fig.5 in MT-031

And what about digital receivers like CS8412 (I'm still using it.. ). Single junction close to the IC too (?) , and to which ground plane Analog o Digital?
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Old 8th January 2019, 06:16 AM   #13
Markw4 is offline Markw4  United States
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Multiple ground planes can get expensive, and may not always be needed. In some cases one ground plane may be preferred over two. In other words, it depends. However, for our purposes here in most cases you should use at least one ground plane. If possible try to think about were ground currents would be flowing and try to be sensible about layout to help minimize any ground noise issues. Designing PCBs is not always a one-shot process. Sometimes more than one design iteration might be needed if any unexpected issues are found during testing. I would suggest trying with one ground plane first. Test the boards you get and make sure the circuit works as expected. If you have problems you can always post here and we will try to help. Most likely, it will be okay.
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Old 8th January 2019, 05:52 PM   #14
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by ygg-it View Post
[I]"Separate analog and digital ground planes should be used... The two ground planes must of course be connected together by a single junction close to the IC.
In practical DIY terms, a single continuously poured ground-plane likely provides an inaudible ground solution. At most, something like what's shown in Fig. 8 of that A.D. document (essentially, a single ground-plane divided in multiple sections which are still connected at one common point (in star-ground fashion) is the most that's practical, or audible, for DIY purposes. Instruments may reveal inconsequentially lower (for home audio) measured noise for a multiple ground-plane solution.

I design and build my own DIY DAC PCBs utilizing common single continuous ground-planes. What I do in addition, is to impedance isolate each chip via ferrite choke and low a inductance ceramic bypass cap on the power supply pins, and the signal inter-connections via inserting a low value resistor in each signal line. This greatly reduces the high-frequency currents circulating on the ground-plane, greatly mitigating any ground-loop interference consequence of utilizing a single common plane. I recall that Guido Tent, of Tent Labs, once published an nice app. note on isolating digital circuits in that manner.

Last edited by Ken Newton; 8th January 2019 at 06:07 PM.
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Old 9th January 2019, 08:23 AM   #15
batteryman is offline batteryman  United Kingdom
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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
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Originally Posted by Ken Newton View Post
I design and build my own DIY DAC PCBs utilizing common single continuous ground-planes. What I do in addition, is to impedance isolate each chip via ferrite choke and low a inductance ceramic bypass cap on the power supply pins, and the signal inter-connections via inserting a low value resistor in each signal line. This greatly reduces the high-frequency currents circulating on the ground-plane, greatly mitigating any ground-loop interference consequence of utilizing a single common plane. I recall that Guido Tent, of Tent Labs, once published an nice app. note on isolating digital circuits in that manner.
I've allowed for inductors in the power traces to both dacs on my dual 1541 and quad ad1862 boards and also 10r resistors in the 4 digital inputs (which are not routed around the board)

My pcb design software generates upper and lower ground planes automatically but dividing these into separate areas is more work so I have, in the past, kept the ground planes, analogue, digital and power supply grounds all separate up to the common point at the off board 0v pin. (ie the ground planes weren't connected to anything except each other)

As you say, I will be surprised if there is an audible difference on such a dac simple design.
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Old 9th January 2019, 08:33 AM   #16
chris719 is offline chris719  United States
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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
High frequency currents will typically return on the reference plane and right under their respective trace (lowest inductance path). If they are causing a problem, you need to re-evaluate your layout and floor-planning. Splitting planes, unless you know exactly what you are doing, is a recipe for EMC issues.
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Old 9th January 2019, 10:26 AM   #17
ygg-it is offline ygg-it  Italy
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Default Sorry forget to say...

Sorry, I forget to say that i'm using exclusively perfboards and not PCB...

Hence, not possible for me to create ground planes but I can only tie multiple wires and create multiple transformer/bridge ground separated power supplies


So question is:

should I have two ground wires (digital and analog) from Power supply (transformer/bridge ground separated?) to the dac/receiver digital and analog ground pins

or

one wire from power supply to the dac/receiver joined digital and analog pins?
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Old 9th January 2019, 10:49 AM   #18
batteryman is offline batteryman  United Kingdom
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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
Quote:
Originally Posted by ygg-it View Post
Sorry, I forget to say that i'm using exclusively perfboards and not PCB...

Hence, not possible for me to create ground planes but I can only tie multiple wires and create multiple transformer/bridge ground separated power supplies


So question is:

should I have two ground wires (digital and analog) from Power supply (transformer/bridge ground separated?) to the dac/receiver digital and analog ground pins

or

one wire from power supply to the dac/receiver joined digital and analog pins?
I would use separate ones but connect a low value inductor between them at the pcb. This keeps HF noise from getting from one to the other, whilst maintaining them at the same DC potential.
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Old 9th January 2019, 12:22 PM   #19
sgrossklass is offline sgrossklass  Germany
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Originally Posted by batteryman View Post
I would use separate ones but connect a low value inductor between them at the pcb. This keeps HF noise from getting from one to the other, whilst maintaining them at the same DC potential.
It also introduces a ground loop, so you have to make sure its loop area is kept to a minimum to avoid stray magnetic field pickup. Not using the very thinnest wire you can find would be another good idea.
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Old 9th January 2019, 01:37 PM   #20
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by ygg-it View Post
Sorry, I forget to say that i'm using exclusively perfboards and not PCB...
I know that it's extra trouble and cost, but you should seriously consider having your own custom PCBs made for you. There are many reasonably priced internet based prototyping services which will do that for you.

Last edited by Ken Newton; 9th January 2019 at 01:52 PM.
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