RE: PCB Antenna Matching Circuit for nRF8001

Carl — Mon, 06 Jan 2014 17:06:15 GMT

Hi Håkon,

thanks for the answer. I was just afrait that it might be harmful for the nRF8001, when the impedance, that is seen by ANT1 and ANT2 differs much from the data sheets recommendation.

I am aware of the effects I have to calculate with, when working with such high frequencies. I did the PCB design with taking care to keep the lines as short as possible. I have to consider the wires parasitic inductances as well as the capacitances towards VCC and GND and other signals. I guess there are interesting and exausting hours awaiting for me:-)

So it seems you recommend to keep the given network, because it also works as sharp filter for the RF circuit. I will add the matching network to the given circuit then.

Greetings, Carl

RE: PCB Antenna Matching Circuit for nRF8001

Håkon Alseth — Mon, 06 Jan 2014 16:42:29 GMT

Hi,

The impedance seen from ANT1/ANT2 pins on nRF8001 is found from simulation, and may be a bit off due to physical layout (PCB, routing, trace width etc) The matching network has two main tasks:

Filtering and suppressing harmonics/spurious.
Impedance conversion (BALUN)

A simple BALUN is quite easy to do, but combining this with a high-order filter makes things complicated. However, when you're also dealing with high frequencies in the GHz-domain, there are physical aspects that comes into play. One millimeter of trace equals ~1nH, you also have stray capacitances between your trace and ground (on both TOP and BOTTOM layer), and when you're tuning components are in the low pF/nH area, everything as a great impact on the end result.

Now, by removing the components L3/C5/C6 you are effectively removing the sharp filter. This will cause harmonics and spurious to reach a level which is non-compliant with most teleregulatory requirements (FCC/ETSI/etc).

Best regards Håkon