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rf pcb design

nidhijani

New Member
Hello,

I am doing my first RF project. i want the help regrading trace width calculations. I have to design 6 Layer PCB in FR 4 material which my first layer contains RF signals.

My layer stack up is like Signal, GND , Inner layer, Power , GND, Bottom.

I have query regarding the RF PCB design.

1) RF signal contains in 1st layer so which calculator used? co planner or Micro strip?
2) How RF Trace length important? any calculator for RF length calculation?


Please guide me as soon as possible as this is my first project and i have to submit it.

Thank you so much.
 

kubeek

Well-Known Member
Most Helpful Member
I suggest you go download saturn pcb toolkit and calculate the trace widths. Also ask your pcb manufacturer, they should have their own recipes for controlled impedance design.
 

nidhijani

New Member
Hello,

I am doing my first RF project. i want the help regrading trace width calculations. I have to design 6 Layer PCB in FR 4 material which my first layer contains RF signals.

My layer stack up is like Signal, GND , Inner layer, Power , GND, Bottom.

I have query regarding the RF PCB design.

1) RF signal contains in 1st layer so which calculator used? co planner or Micro strip?
2) How RF Trace length important? any calculator for RF length calculation?


Please guide me as soon as possible as this is my first project and i have to submit it.

Thank you so much.
Dear Sir,

Thank you so much for your reply.

Please guide me regarding Trace length. It is necessary to calculate length and match length along with trace width.

Thank you
 

DerStrom8

Super Moderator
Most Helpful Member
Hello,

I am doing my first RF project. i want the help regrading trace width calculations. I have to design 6 Layer PCB in FR 4 material which my first layer contains RF signals.

My layer stack up is like Signal, GND , Inner layer, Power , GND, Bottom.
Which software are you using to design the PCB? This would be helpful to know to provide you with more specific answers.

I have query regarding the RF PCB design.

1) RF signal contains in 1st layer so which calculator used? co planner or Micro strip?
My favorite calculators, which I have found to be most accurate, are those at eeweb.com. Here is the single-ended microstrip calculator, though other calculators are also linked to the right on the following page:


Considering you have a microstrip (a trace over a ground plane) then you'll want the microstrip impedance calculator. If you have differential signals you'll want the edge-coupled microstrip calculator. More details regarding what you're designing (perhaps a screenshot) would be very helpful.

2) How RF Trace length important? any calculator for RF length calculation?
Again, more details are required. Trace length is important to match propagation delay of different signals. Some receivers will not behave properly if, for example, the clock signal reaches it before the data signal does. In such a case, suppose the data contains a low-to-high transition and clock tells the receiver to pass the data through before the data is received, instead of clocking through the new high-level signal it clocks in the old low-level signal. Your data which is transmitted will have incorrect bits. It is important to ensure that the signals reach the receivers at the desired time to ensure they are captured properly. Matching trace length isn't as important as matching propagation delay, so that is what you'll need to calculate. Tools such as this one will help you calculate the propagation delay based on your trace dimensions:


As kubeek suggested, I too recommend the Saturn PCB Toolkit. It's free and has a lot of very useful tools for PCB design.

Good luck!
Matt
 

nidhijani

New Member
Which software are you using to design the PCB? This would be helpful to know to provide you with more specific answers.


My favorite calculators, which I have found to be most accurate, are those at eeweb.com. Here is the single-ended microstrip calculator, though other calculators are also linked to the right on the following page:


Considering you have a microstrip (a trace over a ground plane) then you'll want the microstrip impedance calculator. If you have differential signals you'll want the edge-coupled microstrip calculator. More details regarding what you're designing (perhaps a screenshot) would be very helpful.


Again, more details are required. Trace length is important to match propagation delay of different signals. Some receivers will not behave properly if, for example, the clock signal reaches it before the data signal does. In such a case, suppose the data contains a low-to-high transition and clock tells the receiver to pass the data through before the data is received, instead of clocking through the new high-level signal it clocks in the old low-level signal. Your data which is transmitted will have incorrect bits. It is important to ensure that the signals reach the receivers at the desired time to ensure they are captured properly. Matching trace length isn't as important as matching propagation delay, so that is what you'll need to calculate. Tools such as this one will help you calculate the propagation delay based on your trace dimensions:


As kubeek suggested, I too recommend the Saturn PCB Toolkit. It's free and has a lot of very useful tools for PCB design.

Good luck!
Matt
Dear Sir,
Thanks you so much for your prompt reply.

I am using mentor graphics(PADS) software for PCB Designing.
In design its just pure RF signal, Blocks of RF signal are like amplifier, BPF and Amplifier for which i want this information.
So it is necessary to calculate Trace length?

Thank you so much for your support.
 

DerStrom8

Super Moderator
Most Helpful Member
I'm afraid that's beyond my experience. Hopefully someone else will be able to step in here.
 

Ylli

Active Member
What frequencies are you dealing with? If you are in the low MHz, range, it is not much different than an audio design. If you are 100's of MHz or into the GHz range, it's a totally different story.
 

DerStrom8

Super Moderator
Most Helpful Member
And to clarify, it's not really a matter of "calculating trace length". It's a matter of matching propagation delay. Just route your traces so that their propagation delays are about equal, which usually means they are roughly the same length. Overall length is usually not a major concern, though that will depend on the specific application and signals being transmitted. The length isn't really something you calculate though.
 

nidhijani

New Member
What frequencies are you dealing with? If you are in the low MHz, range, it is not much different than an audio design. If you are 100's of MHz or into the GHz range, it's a totally different story.
Dear sir,
Thank you for your reply.

My frequency is about 2.7GHz and 8.2 Ghz.

Thank you
 

Ylli

Active Member
Just be aware the dielectric constant of FR4 is not well controlled, and it is quite lossy at UHF/microwave frequencies.
 

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