ST25R Antenna Matching tool with specific antenna

[LCHAN.41]

Hey, i am developing a RFID reader for ISO-14443-4 card with st25r3917b. The firmware is done and works with my custom MCU board connected with external RF board of STEVAL-25R3916B. However , if I switching the testboard and connect with my custom RFID board ,the reader just can not detect the card .It is obviously cause by wrong matching circuit I draw before.The antenna parameter to the Antenna matching tool is still a question for me to implement a custom antenna for the project.

Due to lacking of newwork analyzer and imformation from the antenna datasheet. Some of the parameter from the Antenna Matching tool is still missing(Target Q , Targeting Matching Z, Parallel resistance and the present box?). Should i just enter some general numbers in the blank? 

In my test , there are three board , one main board only contain MCU(STM32L452CCU6), one STEVAL-25R3916B RF board and one custom st25r3917b board contain RFID antenna with cable(FXR.01.07.0100C.A). In the Antenna Matching tool , the topology is using the config [3916-single-ended-cable]

[Carlo Corlattoni]

Hello,

the FXR.01.07.0100C.A is an already matched 50Ohm antenna. If you intend to use this antenna, you need to select the single-ended-cable configuration in the drop down menu of the antenna matching tool. Since the antenna is already 50Ohm, you don't need to fill the antenna parameters, because in this case we only want to transform the 50Ohm antenna impedance to some lower impedance to connect to one RFO via the matching network. You need to define the EMC inductor, filter frequency and the target matching impedance to calculate the remaining matching components. I would suggest to start with 470nH, Target matching Z=16 Ohm and EMC Filter=22500kHz. The tool should calculate around 106pF for the EMC cap, 360pF for the series cap and 134pF for the parallel cap before the 50Ohm antenna connection. This should give you a reasonable antenna matching of ~16Ohm at 13.56MHz seen from RFO1. (A network analyzer is strongly recommended to verify the matching and impedance curve)

[LCHAN.41]

Sorry for late reply , thank you for the help for filling up the match tool. But i am still have several questions for it .
1. Since the antenna is already tuned to 50ohm ,  so you said[you don't need to fill the antenna parameters], but if i empty the antenna parameters of the tool, the tool would pops up a warning that stop the calculation, do i still need to feed some default parameter to it?.

2, Since the antenna was wired  , so i should select the single-ended-cable configuration. From the suggest parameter of the matching inputs, seems the present drop down menu is set to 16 ohms,what is the purpose of choosing 16ohms? And why the inductor is using 470nH instead of the default 330nH?

3 I studied the AN5276 , the target Q factor still confuse me, this parameter should fill in antenna Q value or the matching circuit Q value?

4.Here is the result base on the datasheet and the parameter you provided, If i do PCB designing , i can ignore the components after the wire in the tools , because it is already on the antenna ,right?

[Carlo Corlattoni · Accepted solution]

Hello,

1) you need to keep the default values in the antenna parameter section, because it wants to calculate the tuning caps for an antenna that is not yet matched to 50Ohms. So, you need some values to calculate the left part of the cable.

2) the purpose of the presets is to give useful tuning results, because not every target matching impedance can be realized and calculated for the 50Ohm case.

3) Since the antenna is already tuned to 50 Ohms and correct Q of the antenna should have been applied, the target Q can also be neglected in this case. The Q factor would play a role if your antenna is not yet matched to 50 Ohms, then a specific damping resistor might be added to achieve "good" waveforms.

4) correct