RF and Low-Frequency Analog Layout

[kbryant]

Hello!

On a PCB I have RF, digital, and analog sections.

RF section has a strong +5 dBm LO feeding the mixer operating in the MHz range.
The analog section consists of an active filter working in the kHz range with much weaker -15 dBm signals.

In PCB practice, power planes (and sometimes ground planes) of the analog and digital sections are usually partitioned and separated.

So my question is: should I separate the RF section from the digital and lower-frequency analog sections as well? Or can the RF section use the same power/gnd planes as the analog?

 

[marce]

This is a hard one to realy answer without intimate knowledge of the circuit. I would reccomend some serious reading of books like Henry Ott, Howard Johnson, Ralph Morrison to name a few

https://www.semtech.com/images/datasheet/rf_design_guidelines_semtech.pdf
A good list of reccomended reading in the link below:
https://www.jlab.org/accel/eecad/pdf/050rfdesign.pdf
RF and Microwave: Design Challenges in PCBs - Mentor Graphics

 

[kbryant]

marce,

Thank you for the suggestions! I have skimmed through Ott's book and have a good idea of the isolation of the analog signals from the digital signals. In general though, do high-frequency analog components in the MHz range share the same power and ground with the lower kHz range analog circuitry?

This is a hard one to realy answer without intimate knowledge of the circuit. I would reccomend some serious reading of books like Henry Ott, Howard Johnson, Ralph Morrison to name a few

https://www.semtech.com/images/datasheet/rf_design_guidelines_semtech.pdf
A good list of reccomended reading in the link below:
https://www.jlab.org/accel/eecad/pdf/050rfdesign.pdf
RF and Microwave: Design Challenges in PCBs - Mentor Graphics

 

[marce]

I have limited RF layout experience, so am hoping someone who is more experiences in this would provide some guidance. From the designs I have seen, the ground has been 1 contigous plane, the supplies were seperated for the RF and the other circuitry.

 

[rupeshchannawar]

I have design the board with RF/ANALOG and Digital section. I have used same ground plane for all sections..and board is working fine... i will suggest u to separate RF and other low frequency parts...Refer below link...

**broken link removed**

https://www.qsl.net/va3iul/Files/RF-Microwave_PCB_Design_and_Layout.pdf

 

[kbryant]

Thank you for your suggestions! I had a question, you mentioned you had the same ground plane for all sections... Did you separate the power plane or did you share the power as well?

I have design the board with RF/ANALOG and Digital section. I have used same ground plane for all sections..and board is working fine... i will suggest u to separate RF and other low frequency parts...Refer below link...

**broken link removed**

https://www.qsl.net/va3iul/Files/RF-Microwave_PCB_Design_and_Layout.pdf

 

[rupeshchannawar]

yes, power plane is separated in each section.... RF Section is separated by Ferrite beads

 

[marce]

On the boards I have seen/worked on had one contigous ground, the RF power isolated by a pi filter of cap-ferrite bead-cap.