Fxth 8700

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Fxth 8700

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riccardocescato
Contributor I

Hi,

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?

Thanks,

Riccardo

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Wlodek_D_
Senior Contributor II

Hello Ricardo,

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).

Regards,

Wlodek

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yapingwang
Contributor I

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?

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