LAUNCHXL-CC13-90: Schematic explanation

Thanks !

One last question, I can't find any document about calculate notch filter like L25/C210 and C24/L207.

Did you have information about them please ?

Hi,

I don't understand what you mean by "calculating notch filter". For a notch filter, one of the most important parameters is the resonance frequency. It can be calculated using the formula f=1/2π√(LC). In this case both L25/C210 and C24/L207 are there to attenuate the second harmonic. If you use the given formula, the resonance frequency of both notch filters is around the second harmonic.

Best regards,

Haiatullah

2097MhzL25/C210

1992MHz C24/L27

Effectively, around twice of 868Mhz, little more than twice. Thanks !

I suppose that, two notch filter in a same RF line, is to reduce twice the harmonic. But why one in shunt and the second in series ?

Hi,

A series LC circuit has the least impedance at the resonance frequency while a parallel LC has it's maximum impedance at the resonance frequency. In this case, the parallel LC blocks the seconds harmonic from being transmitted by providing a high impedance at that second harmonic. The series LC makes a low impedance path for the second harmonic to ground. I hope this makes thing a bit clearer for you.

Best regards,

Haiatullah

This is very interesting, thanks a lot !

And in case of delete the LC series, what we will see ? Less absorption of the second harmonic ? (no path to the ground)

The second harmonic notch is (very) layout dependent meaning that you need to find the notch simulating in ADS or similar and fine tune when you have the PCB. The radiated 2. harmonic is for some reason a lot higher than the conducted value hence two notches are required. If you remove or detune one of them the radiated harmonic will most likely be above the ETSI limit.