Grounding rules in Multi ADC Designs

Shyam Daram

Other Parts Discussed in Thread: THS4541

I have a design as below, where the data conversion is happening at a sampling rate of 500MSPS and signal is of range 200MHZ

There are two adcs in my design,

1. is it correct way to create seperate AGND ground place for two ADCs ?

2. is it ok to common the Digital ground plance for both ADCs ?

3. coming to PGND the dcdc and LDOs will have same PGND which is taken to AGND via bead

4. is it appropriate to common the grounds in a star connection ?

Let me know if any extra care need to be taken.

5. The layout may tentatively look like below.

over 4 years ago

0 jim s over 4 years ago

TI__Guru* 91947 points

Shyam,

What ADC's do you plan on using?

Regards,

Jim

0 Shyam Daram over 4 years ago in reply to jim s

Expert 1305 points

AD5407 as of now, AFE is THS4541, anyway the question is very generic, irrespective of adc

0 jim s over 4 years ago in reply to Shyam Daram

TI__Guru* 91947 points

Shyam,

See attached file for layout recommendations.

Regards,

Jim

0250.Schematic and Layout tips 3-31-22.ppt

0 Shyam Daram over 4 years ago in reply to jim s

Expert 1305 points

My doubt is mainly on Multi ADC boards

Literature like this Multiple ADC Grounding (sigcon.com) has caused this doubt.

0 Rob Reeder over 4 years ago in reply to Shyam Daram

TI__Mastermind 45670 points

Hi Shyam,

Using what sigcom suggests in figure 2 will work. However, it doesn't make much sense. If the ADCs is spanning the analog and digital section/ground area then there is no reason to split grounds or create slotted channels as shown in the literature with sigcon.

For example, return currents stay within the region of origin, so if a digital signal coming from the FPGA or other digital driver is originated there, then its entire loop, return current will stay in that region. It would not flow into the analog domain, cause coupling/noise, then return back to the digital section.

I recommend one ground thru out the board design and make sure all circuits are partitioned well. Meaning, keep digital circuits localized in the digital section and analog circuits localized in the analog section of the board.

Hope that helps.

Regards,

Rob

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Grounding rules in Multi ADC Designs