Here is a schematic of a 13.56 MHz RFID transmitter which can deliver about 2 W into 50 Ohms. M1/M2 are 2 FETs in an SO8 housing. You can increase the output power by increasing V1. You might adjust the voltage divider R4/R5 to get an optimum DC-bias for the FETs. This design is a good starting point. Depending on the parameters of your output filter inductors (parasitic resistance, parasitic mutual inductance due to positioning of L3 ... L5, etc.) there may be additional tuning necessary. Maybe it will be necessary to add more FETs in parallel if you need more power. For V3 you can use a CMOS crystal oscillator, perhaps is some buffering with some 74AHC125 in parallel necessary. If you drive the FETs with a 5 V oscillator, DC-bias adjustment is needed. Depending on your tuning and layout an additional filtering of harmonics, especially 27.12 MHz and 40.68 MHz might be necessary.
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Dear Rf300,

I am reaching out to you once again, and I apologize for the inconvenience. If you don't mind, could you please share the component library for the IRF7103? I would be very grateful for this act of kindness.

 

I am sorry to admit that I don't have a simulation model for IRF7103. I simply used LTspice for drawing the schematic. I selected the IRF 7303 for drawing and changed the name so that you know which type of FET I used. Maybe the parameters of this device are comparable, you have to check the data sheets. Maybe you can find a model at Infineon's web page, they acquired International Rectifier a few years ago.

 

I am sorry to admit that I don't have a simulation model for IRF7103. I simply used LTspice for drawing the schematic. I selected the IRF 7303 for drawing and changed the name so that you know which type of FET I used. Maybe the parameters of this device are comparable, you have to check the data sheets. Maybe you can find a model at Infineon's web page, they acquired International Rectifier a few years ago.

Got it, dear Rf300. Let me try to do this. I may reach out to you again.

 

Make2526, are you sure that the gate driver shown in the diagram will be able to operate at your frequency? I'm not sure.

 

Make2526, are you sure that the gate driver shown in the diagram will be able to operate at your frequency? I'm not sure.

Dear Bordodynov, thank you so much for your kind concern and valuable input. As I am still learning in this domain and benefiting greatly from experts like you and other members, I truly appreciate you raising this point. According to my knowledge and based on the ADuM4221A datasheet (Analog Devices, Rev. B, 2020), I believe this gate driver is capable of operating at 13.56 MHz. Its maximum propagation delay is 44 ns, and since the full period at 13.56 MHz is 73.7 ns, the timing margin is sufficient for Class-DE operation where the dead time is independently controlled via the DT pin resistor. Additionally, it delivers 4 A peak gate drive current, enough to switch the IRF510 gate capacitance cleanly at this frequency, and provides 5700 Vrms galvanic isolation. I fully acknowledge that real hardware performance must be verified on an oscilloscope, and I remain very open to your expert guidance if you see any further concerns or suggest a better alternative.

 

Its maximum propagation delay is 44 ns, and since the full period at 13.56 MHz is 73.7 ns, the timing margin is sufficient for Class-DE operation

44 ns is more than half of the period, therefore Bordodynov's and my concerns. And with an RDT of 47 kOhm you will have a dead time of about 235 ns according to the data sheet.

For what do you need the high voltage isolation? Usually this isolation is needed for power inverters, where there is an intermediate circuit voltage of some 100 V and you have to drive the upper MOSFET with a suitable high voltage.

 

44 ns is more than half of the period, therefore Bordodynov's and my concerns. And with an RDT of 47 kOhm you will have a dead time of about 235 ns according to the data sheet.

For what do you need the high voltage isolation? Usually this isolation is needed for power inverters, where there is an intermediate circuit voltage of some 100 V and you have to drive the upper MOSFET with a suitable high voltage.

Thank you so much for pointing this out, you and Bordodynov are absolutely right, and I completely agree with both concerns. I honestly missed those critical points, and I really appreciate the group's patience and expertise in correcting me. If anyone has a good replacement in mind that would work better for this frequency and application, I would be truly grateful to hear your thoughts and suggestions…

 

Dear all,
I am working on an RF power amplifier designed to operate at 13.56 MHz. I am using the ADuM4221A gate driver IC in my circuit. The issue I am facing is that the output signal from the driver is not correct. More importantly, even the input signals at pins VIA and VIB are not as expected. According to the datasheet and my understanding, these two input signals should be 180 degrees out of phase with each other. However, after running the simulation in LTspice, I am not getting the required phase relationship. I have attached my .asc file for your reference. I would be very grateful if any of the experienced members in this group could kindly take a look at my circuit and guide me on what might be going wrong. Thank you very much in advance for your time and help.

Welcome to AAC.

I am concerned with the legality of the amplifier you are trying to build. Putting a PA on an RFID system would be quite illegal in every jurisdiction I could find. The band is regulated by International treaty and the potential for interference with other RFID systems is very high. Such a device could also be used for malicious purposes.

In any case I don't know what a legitimate application for such an amplifier could be. I am not accusing you of anything, rather I am asking if you could explain how you will use this.

Thanks.

 

Welcome to AAC.

I am concerned with the legality of the amplifier you are trying to build. Putting a PA on an RFID system would be quite illegal in every jurisdiction I could find. The band is regulated by International treaty and the potential for interference with other RFID systems is very high. Such a device could also be used for malicious purposes.

In any case I don't know what a legitimate application for such an amplifier could be. I am not accusing you of anything, rather I am asking if you could explain how you will use this.

Thanks.

Dear Ya’akov,

Thank you very much for your thoughtful reply. As I mentioned in my previous posts, the designed PA operates at 13.56 MHz, targeting the ISM (Industrial, Scientific, and Medical) band specifically for biomedical wireless power transfer (WPT) applications, such as wearable medical devices. There is no other intended purpose.

As a student, I am simply learning and attempting to design this circuit solely for biomedical wireless power transfer (WPT) applications. Thank you for your understanding.