Request for Schematic and PCB Layout Review – Wireless ECG System Using nRF5340 and nRF7002

[Abdelrahman Elsissy]

Dear Nordic Engineering Team,

I am currently developing a wireless ECG acquisition system based on the ADS1298 analog front end (AFE), the nRF5340 SoC, and the nRF7002 Wi-Fi 6 companion IC. The goal of this project is to interface the nRF5340 with the ADS1298 to acquire the 12-lead ECG signals in real time and transmit them over Wi-Fi, utilizing the nRF7002 Wi-Fi 6 companion IC.

The system is composed of two custom-designed sections:

• Analog front end, including the power management circuit, input protection, and the ADS1298 AFE.
• Digital section, featuring the nRF5340 SoC for processing and the nRF7002 for wireless transmission.

I have completed both the schematic and a multi-layer PCB layout. Given the complexity of the design , I would be grateful if your team could kindly review the schematic and layout and share any feedback or suggestions for improvement before final validation. Please find the schematic and PCB documents attached

Additional details:

• COEX is not required, as Wi-Fi is used exclusively for data transmission.
• The system is configured for normal voltage mode, with DVDD powered at 1.8 V.

Thank you very much for your time and support. I look forward to your insights.

Best regards,
Abdelrahman

12_Channel_ECG.pdfpcb_layers.pdfPCB2.pdf

[Bendik Heiskel]

Hi Abdelrahman,

nRF5340:

• If you are using the USB peripheral, 5V from the USB connector must be supplied to the VBUS pin, and DECUSB needs a 4.7uF capacitor:
  
• 8.2pF load capacitor for the 32MHz is too low. A crystal with a CL=8pF needs 12pF load capacitors. This is calculated using the following equation:
  C = 2*CL-C_pin
  Where C_pin is 4pF for the nRF5340. This equation is a simplified version of the one listed in the datasheet, with the assumption that C1=C2 and C_pcb1=C_pcb2=0pF:
  https://docs.nordicsemi.com/bundle/ps_nrf5340/page/chapters/oscillators/doc/oscillators.html#ariaid-title2
  The same applies for the 32.768kHz crystal, since no part number for this crystal is listed I can't double check, but 8.2pF seems very low.
  The nRF5340 have configurable internal load capacitors for both the HFXO and LFXO, so C68, C69, C116 and C117 can all be removed or marked NC/DNP.

nRF7002:

• The nRF7002 have internal load capacitors for the 40MHz crystal, C83 and C84 should be removed.

Layout:

• A GND fill should be added to the top layer, this is especially important around the nRF7002 RF traces and antenna, and around the crystals.
• FL1 should be rotated and moved closer to the nRF7002, to minimize the length of the TXRF0 and TXRF1 traces, like in the nRF7002 reference layout:
  
• These 2 traces on the second layer must be rerouted, such that they don't cross under the RF traces from the nRF7002.
  
• The thermal relief should be removed from the GND vias under the nRF7002 and nRF5340, these vias need a good connection the internal and bottom layer GND fills.
• The GND vias under the nRF5340 should connect to the GND fille on L2.
• The pinout of the 40MHz crystal looks off, usually the signal pins are 1 and 3 not 1 and 2. You should double check if the footprint used is matching the pinout of the crystal you are using.
• The GND cutout under the crystals should not extend to the bottom layer. The bottom layer should have GND under the crystals to shield them from picking up noise.
• The grounding of C25, C26, C24 and C27 should go to the isolated part of the GND fill on the top layer, and connect to a semi isolated part of the L2 ground fill. This is done to sum the GND return currents and cancel out noise from the buck converter. Here is how this is done in the reference layout:
  

Feel free to upload a updated design, and I can take a second look at it.

Best regards,

Bendik

[Abdelrahman Elsissy]

Dear Benedik,

Thank you so much for your prompt response.

I will update my design based on your feedback and will send a second version for your review.

Have a great day.

Kind regards,

Abdelrahman