what is the impedance of RF pin of FXTH87?

cancel
Showing results for 
Search instead for 
Did you mean: 

what is the impedance of RF pin of FXTH87?

188 Views
anthonyhhfu
Contributor II

hi,

I am doing the impedance matching of TPMS using fxth87 IC. My antenna is using valve of tire but I cannot find the output impedance of RF pin in the data sheet. I try to calculate from the schematics of SCH_TPMS_FXTH870911-434.pdf. The result is 3.936+j76.49. is it correct?

btw, is it possible to support dual frequency of 433.92Mhz and 315Mhz at the same time?

thanks,

Anthony

Labels (1)
0 Kudos
3 Replies

81 Views
TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Anthony,

Please find below the answer from our TPMS RF expert:

I never realized a common 315MHz - 434MHz matching network as I generally optimize both frequency (for CZ context in particular), therefore two matching networks are usually worked out. Nevertheless it is something that can be envisage, but with few dBs losses on each frequency..

 

I attached a document showing the location of impedances that have to be presented to the RF pin for both frequency. Depending whether he has access to the RF pin directly (probe station) or by means of a SMA connector as I proceed myself, impedances are reported within this document

 

For example, at 434MHz and power step 5 dBm, the optimized impedance at the SMA plane is somewhere about 201+j*238, whereas at the RF pin (SMA connector deembedded), the target is 114+j*214

Best regards,

Tomas

0 Kudos

81 Views
anthonyhhfu
Contributor II

hi Tomas,

thanks for the reply. we are using the RF coaxial cable as attached to probe the RF pin directly. By doing port extension we can move the reference plane to RF pin. So I think we should take "Impedance at the RF pin". 

After reading the attached file, I still have the question:

What is the difference of "Matching CZ" and "Matching 3V"?Does that use different circuit?

Can I get RF Application note with the complete impedance data at all the power steps at 315Mhz and 434Mhz because we need to optimize the battery life.

Can the impedance data be a port impedance file like S1p format and used in EM simulation SW for impedance matching?

regards,

Anthony

0 Kudos

81 Views
TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Anthony,

We have no other data to provide in addition to the one attached earlier. They are issued from loadpull measurements and as you can see there no so much difference between power step 5dBm and power step max for example. Therefore, targeting an impedance somewhere around impedances indicated should allow to get a quite good RF range.

 

The difference between matching “CZ” and matching “3V” is indicated just above the tables. The matching “CZ” is the impedance targeted during our CZ exercise. This impedance allowed to reach all requirements in term of minimum output power over Trange and Vrange (domain of minimum output power is reported within the datasheet, it is either 3dBm or 5dBm according to battery and temperature ranges). The “3V” is the impedance allowing to reach the maximum output power at 3V, but cannot meet all expectations at some corner of the domain with good enough Cpks (> 1.67). The “CZ” one has been moved away a little bit from the “3V” so that requirements at critical combinations of temperature and voltage (for example 125°C and 2.5V, or 1.8°C and 0°C) are fulfilled.

 

Otherwise, yes, the impedance measured can be imported in an EM simulation as an s1p file, but it is customary difficult to get a reliable enough EM simulation (with PCB and antenna) so that the matching network could be extracted. Can be used to get a first starting point, then a refinement stage needs inevitably done at lab level.

Best regards,

Tomas

0 Kudos