FEDEVEL
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barakg , 06-24-2017, 11:39 AM

Hi,

First of all I'll apologize for my newbish question

I've always wondered why do we have the option "Impedance control" in some PCBs manufactures when quote a PCB.
If I have the specific PCB stack-up from the manufacture and according to these data I calculate and gets the width of the signal to achieve the required impedance, considered the manufacture capabilities. so if I get it right, the manufacture will manufacture the PCB with the width that I did in the design according to the DFM files that I supplied in my order.

So, Why do I need this option "Impedance control"? What else the manufacture do?

Thanks.

robertferanec , 06-24-2017, 11:55 AM

It is much more complicated. I am preparing a video about that.

For example, during PCB manufacturing they have to heat up the materials and press them (they call it lamination) - and during the process some properties of materials will change e.g. thickness of prepreg. So, theoretical calculations are only approximate, they have to adjust the parameters based on their experience.

barakg , 06-24-2017, 01:03 PM

So the calculations that I did in, lets say, PCB Toolkit, are not correct?

robertferanec , 06-26-2017, 12:20 AM

They are approximate.

MadhuWesly , 08-11-2017, 01:45 AM

Hi Robert,
I have a query reg. RF PCB design, hope you answer. Thanks in advance.
Image(PFA) explanation:
The attached image is the "output end of a power amplifier(PA)", which gives 1.5-j1.7Ohm impedance at output pads(12th & 10th) of the PA. And then it is being matched to 50 Ohm single ended impedance using matching circuitry.
From the following link I have understood that "we no need to worry about controlled impedance when trace length is less than 1.6 cm in my RF PCB design."

Should we maintain the same impedance for the traces carrying RF signal line?

https://electronics.stackexchange.com/questions/322750/should-we-maintain-the-same-impedance-for-the-traces-carrying-rf-signal-line

I'm designing a application circuit board which is having a power amplifier to amplify the RF signal.Does the lines carrying the RF signal should have same impedance say 50 ohms?Also does the sig...

Note: we have replaced strip-lines in the schematic with inductors.

Questions:
1. Do I need to worry about impedance matching in this design since there is already matching circuitry for achieving 50 Ohm at the end?

2. Is it OK if I start drawing the trace of 50 Ohm impedance from the output pads of the PA though at that points the actual impedance is 1.5-j1.7 Ohms?
3. From where to where I have to consider as total trace length whether from output pads(12th & 10th) of the power amplifier to open end(RF OUT - the end point where the antenna is connected) or length of each Trace segment between the pad to pad(or component to component)?
Awaiting your reply.

Best regards,
Madhuwesly.