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RFID 13.56Mhz power amp design

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newbie007

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13.56 mhz receiver

Hi all. I wish I had found this forum a little sooner.

I'm trying to design a RF power amplifier to work at 13.56Mhz. I'm trying to amplify the transmit power from a Texas Instrument TRF7960 reader IC. I want an output power of 8 Watts to power up an antenna that I have built. Reason for this much power is we want to be able to achieve a read range of 1meter. I'm stuck on the power ampflier. Whatever i've designed is not giving me any gain. but a loss. I have simulated my design and it gives me a gain of 9, however when built on a breadboard I'm not getting what is desired.

Some input would be appreciated. attached is a design schematic

thanks.
 

13.56mhz transmitter

By design, the amplifier output power is limited to a few mW. Fortunately this assures survival of the 2N2222 which won't be able to deliver the said 8W output, at least not in a linear PA.

If I remember right, a 13.56MHz PA has been discussed some weeks ago at EDAboard, I suggest to search a bit more thoroughly.

When extending RFID operation volume, the respective regulations for maximum far field should be observed (if a legal application is intended).

As another remark: A 13.56 MHz "antenna" should be regarded rather as an inductive coupler. It is used in a resonant circuit and the input power is mainly consumed by resistive losses. With a suitable coupler design, it's not necessary to dissipate several watts for a 1 m range to my opinion.
 

13.56mhz power amp

okay. i built that amp on PCB and it works... but i'm not getting the desired gain i need. I'm thinking that i need to design a different, smaller antenna for this to work. i'll look into inductive coupler as mentioned.
 

13.56mhz power amplifier

In your actual prototype did you install bypass capacitor(s) to power supply?
 

13.56 mhz hf antenna amplifier

Nope. The schematic above is exactly what I built

Added after 1 hours 12 minutes:

Hey all. I'm a little stumped on how to perform impedance matching between the antenna and the amplifier. The antenna i built was built to spec and had an impedance of 50 ohms. Now i know i must match it with my transmit signal but i don't know what components to use. unfortunately i don't have a network analyzer to give me the specific real and imaginary values.

i've attached a block diagram of what i have.

the capacitive coupling block is what is tuning the antenna for 50 ohms.

thanks for the help.
 
rfid coupler 13.56

You need to install bypass capacitor of 4700pF. You may tune your matching circuit without network analyzer with FM receiver. Put receiver at the distance that provide light coupling to the transmitter and then tune matching circuit until you get the best signal from receiver. Reduce coupling when signal become strong.
 

amplifier 13.56mhz rfid by power amp

the bypass cap is used to kill off the AC going back to the supply ? i'll give that a try. I'll have to check and see if i can get a FM receiver for 13.56mhz.

thanks.
 

13.56 mhz rf power amplifier

Sorry, I mistakenly told you about FM receiver. Your application is 13.56MHz. Bypass capacitor for this frequency must be 470000pF or 470nF. You need receiver for this frequency not FM. Or you can use field meter which is just a resonant tank, tuned to desired frequency and piece of wire as antenna. Connect simple amplitude detector to this tank and you have a field meter. Place it at the distance when coupling to the transmitter is minimal and tune your matching circuit. Reduce the coupling when signal becomes stronger. This is old and well proven method for tuning homemade RF circuits.
 

uh of rfid inductance 13.56mhz

humm. i was thinking of using a spectrum analzyer, which can detect 13.56mhz frequency. Use a pi-network to impedance matching of the transmitter to the antenna. the only problem is with the pi-network I dunno what values to start with... should they be variable caps and inductors ??

I'm pretty sure my antenna is tuned to the proper 13.56mhz because when i hook up a frequency generator to it the spectrum analyzer picks it up. The problem i'm having is when i hook up a transmitter that sends 13.56mhz to a amplifier, there is an impedance mismatch between the output of the amp with the tunning circuit of the antenna.

thanks for the input.
 

13.56 amp

When you told that you have no network analyzer I decided that you have no access to RF test equipment. If you have it you may use spectrum analyzer instead of receiver or field meter. Moreover, you may build PI or T match circuit with adjustable caps and coil (there are a lot of coils with roller contact) and tune your matching circuit. Then just measure obtained Cs and L. Another way is to use the magazines of C and L if you have them in your lab. 13.56 MHz is not so high frequency, so it is possible to connect such devices without disturbing the circuit.

If you want to check how well your antenna is tuned try to change the frequency of signal generator and watch antenna response with spectrum analyzer. You will see where your antenna has maximum efficiency. Turn on MAX HOLD and you will see the plot of antenna gain vs. frequency.

If you know the impedance of transmitter and antenna send the numbers to me and I will return a few possible matching circuits to you.
 

rf spectrum rfid 13.56

Reader IC manufacturers, e.g. Philips/NXP have data sheets and application notes that discusses antenna matching. Knowing the L and R of your coupler coil, you are able to calculate a matching circuit and necessary input power to achieve a certain field strength at the tag location.
 

read block trf7960 forum iso15693

If your project is not your own but for the company, it probably make sense to buy impedance analyzer or one port network analyzer. I bought MFJ-259B impedance analyzer for my home lab only for $260. This analyzer can work from 1.8 to 170 NHz. Later I saw on the Internet one port network analyzers. The price from $400 to $1400 and they were looking well. It may be good alternative to very expensive VNA.
 

rfid 13.56 class e amplifier

The project is my own. I wish i had the use of a network analyzer. It would makes things that much easier. So i don't know the impedance of the antenna but the transmitter data sheet list two things;

- load impedance at the Transmitter is 10 ohms

- Transmit Output impedance is 4 ohms at full power.
 

13.56 mhz amplifier ic

I assume, your talking of the basic transmitter rather than your power amp.

The impedance of the "antenna" is simply the inductance of the conductor loop, e. g. several uH plus the loop resistance at 13.56 MHz (mainly skin effect defined) plus the radiation resistance. Both resistive components can be expected around 0.05 to 0.1 ohm each (with your massive 1" tube). All parameters can be estimated from basic equations given in RF textbooks, I think.

You should consider loop current/voltage of several A and several 100 V already below 1 W output power.
 

rfid 13 mhz amplifier

@newbee007

If you really find you still need a power amplifier for 13.56MHz, you may consider these papers:

https://www.microsemi.com/micnotes/APT9403.pdf

https://www.microsemi.com/micnotes/APT0001.pdf

These discuss some hundred watts output power amps but when you use the included formulas you can work out the 5-10W output you need and choose cheap power MOSFET type accordingly.

With your 2N2222 type transistor here is a friendly paper on a Class-E 13.56MHz amplifier (of course maximum in the few hundred mW output power range only): https://www.st.com/stonline/products/literature/an/10429.pdf This includes antenna matching topics too.
regards, unkarc
 

amplifier 13.56 mhz

A series C/parallel C matching circuit as shown in the ST application note would be most likely suitable to adapt the coupler to a real transmitter impedance. For small bandwidth ISO 15693, no damping resistors are needed for sure.

As a 1 m diameter loop has a non-neglectable radiation resistance and some resistive losses anyway, 0.5 to 1 W may be needed for ISO 15693 minimal field strength of 0.15 A/m at 1m distance.
 

if any one has design 13.56mhz power amplifier for delivering 1 watt power for medical application
 

@newbie007

What about your RFID long range reader project with TRF7960???
Does your power amp work well?
What about your read range?
Have you already read a tag at ~1m????

Two years ago I started to develop a long range reader project with IDS-R13MP.
It is the identical RFID Reader IC like the TRF7960.
I had the same goals like you:
~1m read range
5-12W power amp
...

However I noticed that the TRF7960 generates digital noise which fell on the frequency where the tag reply is expected when driving my big antenna with >1.3W. Due to the sensitivity of my own developed receiver, I was able to see the digital noise generated by the TRF7960, but I was not able to anything against it.
I had many conversations with IDS till they had admitted the fault.

Now I am working on my own RFID 13.56MHz reader without any RFID Reader IC.
..
 

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