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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 7th January 2019, 09:51 AM   #1
ygg-it is offline ygg-it  Italy
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Default Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers

This is the general suggestion of TI, ADI and Maxim for low digital current chip, like DAC and Digital receivers with separate AGND and DGND.
(Not suggested for high digital current devices like DSP)

Don't want to debate the articles, but I would like to know if you really do in this way (join GNDs at chip pin level) with DAC and receivers (like CS84xx) even if you have separate Analog/Digital Power supply regulators (or even separate rectifiers and transformers).

http://www.hit.bme.hu/~papay/edu/Acrobat/GndADCs.pdf

https://www.analog.com/media/en/trai...?doc=cn288.pdf

http://www.ti.com/lit/an/slyt499/slyt499.pdf

Last edited by ygg-it; 7th January 2019 at 09:53 AM.
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Old 7th January 2019, 02:36 PM   #2
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by ygg-it View Post

Don't want to debate the articles, but I would like to know if you really do in this way (join GNDs at chip pin level) with DAC and receivers (like CS84xx) even if you have separate Analog/Digital Power supply regulators (or even separate rectifiers and transformers).
Yes. Both grounds are needed by, say, a dac chip, and they shouldn't be at different voltages at the chip so they need to be tied together there. Also, it often does have some beneficial effect on sound quality to use multiple regulators and or power supplies.
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Old 7th January 2019, 02:52 PM   #3
dewdrop is offline dewdrop  Singapore
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Yeah! I was wondering too.
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Old 7th January 2019, 08:21 PM   #4
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
I am also pondering this for my latest dac pcb.

Why isn't it that the noisier digital ground (from ground bounce) will pollute the clean analogue ground?

I would have thought it best to keep them separate up to the 0v pcb connection to the psu, or even connect the two grounds direct to the psu separately.

Analogue Devices AD1862 dac datasheet supports this by referring to analogue ground common and digital ground common points and they connect at one point only:-

GROUNDING RECOMMENDATIONS The AD1862 has two ground pins, designated analog ground (AGND) and digital ground (DGND). The analog ground pin is the “high-quality” ground reference for the device. The analog ground pin should be connected to the analog common point in the system. The reference bypass capacitor, the noninverting terminal of the current-to-voltage conversion op amp, and any output loads should be connected to this point. The digital ground pin returns ground current from the digital logic portions of the AD1862 circuitry. This pin should be connected to the digital common point in the system. As illustrated in Figure 7, AGND and DGND should be connected together at one point in the system.
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Old 7th January 2019, 08:29 PM   #5
zgtc is offline zgtc  Europe
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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
quoting Douglas Self in his book Small signal audio design:
Quote:
Separate analog and digital ground planes should be used. Most conversion ICs have their analog and digital interfaces at opposite ends or opposite sides of the package, facilitating the use of separate ground planes. It is usually best to run the analog ground plane under the IC to minimize the coupling of digital noise. The two ground planes must of course be connected together at some point, and this should be implemented by a single junction close to the IC.
Also, about Analog Devices, yes, have a look at MT031 tutorial (Grounding Data Converters and Solving the Mystery of "AGND" and "DGND" )

Last edited by zgtc; 7th January 2019 at 08:44 PM. Reason: link to AD tutorial
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Old 7th January 2019, 08:39 PM   #6
Terry Demol is offline Terry Demol  Australia
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Originally Posted by batteryman View Post
I am also pondering this for my latest dac pcb. <snip>
At some point, inside the DAC chip, the digital part must interface with the analog side of the chip. If, for example, you have separate ground planes and join them physically away from the DAC chip, then at said interface point, there will be noise between the grounds which means that noise will be in the signal.

The grounds must be joined at the DAC.
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Old 7th January 2019, 08:50 PM   #7
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
That makes sense. So what about the other components connected to analogue ground? Should these all be connected to the dac analogue ground pin by traces and then the analogue and digital ground pins be joined at the dac. Or, can everything simply be connected to the ground planes at the component and dac ground pins? (ie there are no ground traces)
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Old 7th January 2019, 08:52 PM   #8
zgtc is offline zgtc  Europe
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Do you really tie Analog GND and Digital GND at pin chip level in DAC/Receivers
If I understood the tutorial by AD linked above correctly, traces should be avoided, and use of vias to ground planes encouraged.
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Old 7th January 2019, 09:10 PM   #9
Markw4 is offline Markw4  United States
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Regarding ground planes, I have only been using one, but the ground return connection going back to the digital power supply is at the side of the digital end of the dac board. The analog ground return is down at the other end where the output stage is. If you look at the dac board and try to visualize where ground currents have to be flowing, mostly they are pretty much out of each other's ways. That means digital ground currents aren't modulating the ground voltage in the analog circuitry and vice versa (at least to a reasonable approximation). Of course, the digital and analog grounds are only tied together at the ground plane.

Last edited by Markw4; 7th January 2019 at 09:14 PM.
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Old 7th January 2019, 09:17 PM   #10
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
Yes that would be my preferred way but not so easy with two TDA1541. Pity Philips didn't keep Dgnd close to the digital pins, in fact Agnd is where Dgnd should be.
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