Post History
The schematics in your question are too small to read, and the link you gave goes to some product page, not a datasheet. I'll therefore only answer generic questions. If I am using only one groun...
#2: Post edited
by
Olin Lathrop
·
2025-07-11T20:22:37Z (about 1 year ago)
- The schematics in your question are too small to read, and the link you gave goes to some product page, not a datasheet. I'll therefore only answer generic questions.
- <blockquote>If I am using only one ground plane,in that case do I need to use separate regualtors for AVDD and DVDD?</blockquote>
- The two concepts are independent. A split ground plane will often get you into more trouble than it solves. A good solid ground while keeping any substantial ground currents away from the ground plane near the device is usually more reliable to implement without messing it up.
- Digital chips can change their power current demand very suddenly. This will cause some noise on those supplies. Good bypassing reduces that, but there will always be some. A second supply for analog-only parts of the circuit can be useful so that those parts have a clean supply. Your A/D is apparently 16 bits. If that is spread over a 3.3 V range, then each LSB is only 50 µV. That's the sort of level you want the A/D supply to be clean to.
- Your first strategy should be to locally contain the high frequency currents injected onto the supply by the digital section. That means everything digital related to the chip has its grounds connected together, with only <i>one</i> connection from that net to the main ground plane. Most of the nasty high-frequency current will run in the loop from the chip to the bypass cap and back to the chip without every crossing the ground plane. Only the net better-filtered currents leave the immediate local ground and pass on the ground plane. These will cause less ground offset.
- If you don't use a separate supply for the analog parts, then at least filter the supply. For microcontrollers with 12 bit A/Ds, I usually add a small series chip inductor followed by 20 µF or so to ground in front of the analog power pin. For more sensitive circuits, I've used two such L-C low pass filters in front of a linear regulator to make an especially clean supply. Here is a snippet of the schematic of a commercial product where I did that:
<img src="https://electrical.codidact.com/uploads/tfvufyzt98j28s1be97dsovvui85">
- The schematics in your question are too small to read, and the link you gave goes to some product page, not a datasheet. I'll therefore only answer generic questions.
- <blockquote>If I am using only one ground plane,in that case do I need to use separate regualtors for AVDD and DVDD?</blockquote>
- The two concepts are independent. A split ground plane will often get you into more trouble than it solves. A good solid ground while keeping any substantial ground currents away from the ground plane near the device is usually more reliable to implement without messing it up.
- Digital chips can change their power current demand very suddenly. This will cause some noise on those supplies. Good bypassing reduces that, but there will always be some. A second supply for analog-only parts of the circuit can be useful so that those parts have a clean supply. Your A/D is apparently 16 bits. If that is spread over a 3.3 V range, then each LSB is only 50 µV. That's the sort of level you want the A/D supply to be clean to.
- Your first strategy should be to locally contain the high frequency currents injected onto the supply by the digital section. That means everything digital related to the chip has its grounds connected together, with only <i>one</i> connection from that net to the main ground plane. Most of the nasty high-frequency current will run in the loop from the chip to the bypass cap and back to the chip without every crossing the ground plane. Only the net better-filtered currents leave the immediate local ground and pass on the ground plane. These will cause less ground offset.
- If you don't use a separate supply for the analog parts, then at least filter the supply. For microcontrollers with 12 bit A/Ds, I usually add a small series chip inductor followed by 20 µF or so to ground in front of the analog power pin. For more sensitive circuits, I've used two such L-C low pass filters in front of a linear regulator to make an especially clean supply. Here is a snippet of the schematic of a commercial product where I did that:
- <img src="https://electrical.codidact.com/uploads/tfvufyzt98j28s1be97dsovvui85">
- <blockquote>But if you are using this LC filter infront an LDO which powers both AVDD and DVDD,will this helps.</blockquote>
- You don't. The carefully-filtered supply should only be used to power analog parts of the circuit. Those parts don't suddenly change their current demands as a digital bit flips, and are the parts that are more sensitive to power supply noise. Power the digital parts from the "regular" 3.3 V (or whatever) supply.
#1: Initial revision
by
Olin Lathrop
·
2025-07-11T11:46:20Z (about 1 year ago)
The schematics in your question are too small to read, and the link you gave goes to some product page, not a datasheet. I'll therefore only answer generic questions. <blockquote>If I am using only one ground plane,in that case do I need to use separate regualtors for AVDD and DVDD?</blockquote> The two concepts are independent. A split ground plane will often get you into more trouble than it solves. A good solid ground while keeping any substantial ground currents away from the ground plane near the device is usually more reliable to implement without messing it up. Digital chips can change their power current demand very suddenly. This will cause some noise on those supplies. Good bypassing reduces that, but there will always be some. A second supply for analog-only parts of the circuit can be useful so that those parts have a clean supply. Your A/D is apparently 16 bits. If that is spread over a 3.3 V range, then each LSB is only 50 µV. That's the sort of level you want the A/D supply to be clean to. Your first strategy should be to locally contain the high frequency currents injected onto the supply by the digital section. That means everything digital related to the chip has its grounds connected together, with only <i>one</i> connection from that net to the main ground plane. Most of the nasty high-frequency current will run in the loop from the chip to the bypass cap and back to the chip without every crossing the ground plane. Only the net better-filtered currents leave the immediate local ground and pass on the ground plane. These will cause less ground offset. If you don't use a separate supply for the analog parts, then at least filter the supply. For microcontrollers with 12 bit A/Ds, I usually add a small series chip inductor followed by 20 µF or so to ground in front of the analog power pin. For more sensitive circuits, I've used two such L-C low pass filters in front of a linear regulator to make an especially clean supply. Here is a snippet of the schematic of a commercial product where I did that: <img src="https://electrical.codidact.com/uploads/tfvufyzt98j28s1be97dsovvui85">