In mixed signal design with multiple analog and digital functions, there's no reasonable way to use separate analog and digital grounds. A continuous common ground plane is the usual solution. Separate power supplies may be helpful, but more important to bypass the power supplies near each mixed signal device.
For sure you may read an "audio amplifier´s datasheet" if you think it makes sense.the fact that this is an ADC chip has not actual relevance as it could even be an audio amplifier with digital processor or whatever.
In my eyes their approach fully makes sense. The regulator is located outside the analog section .. still I recommend the analog supply regulators to be located near the ADC. The star point of both GNDs should be located close to the ADC .. inbetween regulators and ADC.I thought the output caps of the analogue (3.3A) regulator should go to AGND but in this circuit, they have connected then to the Digital GND.
placement wise..You mean that the analog section only starts AFTER the 10Ohm series resistor.
you will need amplifiers.in the upper nV range.
I am actually really worried about noise.
Yes, ideally I need amplifiers with a gain of 1000 or even 1500.placement wise..
you will need amplifiers.
And if the sensor signals are in in the nV range, then sensor supply, sensor wiring, shielding and filtering needs to be done very carefully.
Klaus
Hi,
hopefully you recognized the ADC´s ENOB to be somewhere worse than 16 bits.
If you want some signal quality ... then you will need an amplifier, maybe not that high gain, and equipped with a pot for offset adjustment.
For sure digital pots would make the offset adjustment as easy as pressing a button.
What´s the expected data rate per channel?
Also mind the offset DRIFT of typ. 500nV/°C.
Klaus
I thought the output caps of the analogue (3.3A) regulator should go to AGND but in this circuit, they have connected then to the Digital GND.
The ADC chip AGND pins and local decoupling caps are the only parts connected to the AGND.
Is that correct and what would be the reasoning behind that configuration?
Please see picture
Best regards
X
The reason is in order to have an accurate Ground for the ADC, there must be one and only one point of reference for ground from which all return currents flow independently of this measurement. It is commonly called a Star-ground as this point is the centre of the star. It may be supplied by a low impedance ground plane, but there is still only one point. This because Ground by definition means 0V and can only exist at one point unless the shared points have no current flowing between them.
This is shown on page 56 of the datasheet when I searched for "ground".
View attachment 190645
Sorry TL;DR your diagramsIn this diagram, all decoupling caps after the VA supply got to AGND, which is what I thought it should be but in the schematic I asked about, also in (this datasheet somewhere), the decoupl ing capacitors after the VA to DGND instead. That is why I asked.
You need to differentiate beween "capacitors for the voltage regulators" and "capacitors for the ADC"I asked about, also in (this datasheet somewhere), the decoupl ing capacitors after the VA to DGND instead. That is why I asked.
The benefit of using a MUX would be that you can use Dana`s approach of post#10.Do you think such a low signal level is suitable for multiplexing through a Analog MUX / Switch?
I think it's not the appropriate ADC for your application. (25 S/s, nV resolution). If these are strain gauge bridges, we would use modulated bridge supply if ever possible, eliminating the need for offset compensation. If not possible some kind of auto-zero would be applied. It's your job to determine if effective input resolution with internal PGA is sufficient.The Microchip MCP3913 has a PGA as well but no offset compensation.
I have not (yet) found any ADC chips with such offset compensation.
I still think the sensor internal offset generates a high sensor AC (modulation) signal, in a way that the true signal of interest is much smaller.eliminating the need for offset compensation.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?