Aid in Decoding CIrcuit Function

[robismyname]

I need help identifying the purpose for the circuit components in the schematic. To the far left (SR_ANTD) is the connection to the antenna. To the right of the antenna connection there is a JFET?-not sure(Q17) keep moving right you will see a Resistor (R139 - 100K) connected to 3.1V, a ferrite bead connected to 3.1V, I believe another JFET?-not sure(Q13). Below the JFET-not sure (Q13) there are two cap's (C184) and (C185) connected to ground and then a resistor (R111) and an inductor (L31).

I have a few question based on the schematic.

1)Are Q17 and Q13 JFets?
2)Why are there two caps (C184 and C185) connected to ground?
3)Why is one .1UF and the other 22PF?
4) Why is the Resistor and Inductor in series?
5)Why is there a 100K resistor located at the AVCC_3.1V?
6)Why is there a Ferrite Bead connected between the 3.1V and JFET? Why not just a resistor or a cap?

I understand CAP's - that is cap reactance Xc = 1/jwC, current leads voltage, stores energy as electric field but I dont understand why it is used the way it is used in this circuit

I understand Induc - that is induc reacteance XL = jWl, Votage leads current, energy is stored as magnetic field but I dont understand

I understand Resistors - no Reactance

I understand complex numbers and impedance (R+jX)

Apparently not too well if I cant figure out the whys in this circuit. What am I missing other than a good brain?

Please enlighten if it not too much trouble.....

 

[Mazz]

To the far left (SR_ANTD) is the connection to the antenna.

SR_ANTD is the control signal that powers up the RF amplifier U17.
All the circuitry you are analyzing is the supply/power up of this amplifier.
Q17 is a NMOS, Q13 is a PMOS. they are used as switches here.
R139 is a pull-up resistor (when SR_ANTD is undefined, this keeps the Q13 gate to VCC, so Q13 is open).
Q17 acts as a simple inverter. When SR_ANTD is low Q13 is on and Supply current flows in FB10-Q13-R111-L31-U17(6) and FB10-Q13-U17(4), so the amplifier is on.
Node U17(4) need to be a low impedance one: so there are the two C184,185. Why two? Real capacitors have parasitics (you can model this parasitic as a series inductor with cap). This means that its impedance, from a certain freq (Cap's Resonant freq.), becomes inductive and rises up when freq. increases. The large cap has lower resonant freq, the small one has higher resonant freq. the two in parallel guarantee a larger freq range in which the inpedance in this node is small.

R111, L31: This is the Amplifier choke inductor (maybe it's load also). the resistor decrease inductor's Q.

FB10 guarantees isolation for low freqs noise coming from AVCC_3.1.

You are not missing at all a good brain, maybe some experience.
Most probably, if you search some application notes of U17 (in manufacturer site...) you'll find a very similar circuit, with more explanations.

I hope it can help.
Mazz