I'm using the chip Fxth8700 for a TPMS project.
I need help to design the matching network for the antenna (433MHz) , because I'm not expert on that field.
Q1) Why there is L1 between Vdd and the RF pin? Which value should it have?
Q2) Has the RF pin a source impedance of 50 ohms?
Please refer to Xtrinsic FXTH87 Family Evaluation Design Reference Manual (http://cache.freescale.com/files/sensors/doc/ref_manual/FXTH87EDRM.pdf ).
In chapter 3.2.2. you will find recommended values of components in matching network.
Regarding your question: in simplest words the function of L1 is to "separate" RF from Vdd at working frequency (315 or 432 MHz).
I design the PCB as the referenc, but the matching is not good....
Set the input power to 0dm, connect it to Spectrum Analyzer by coaxial directly , just -40dBm power is tested.
It sugest the matching is so bad...
How to improve?