How RFID Works? and How to Design RFID Chips?

in this video we learn about how RFID works and we see what is inside RFID tags or cards which you use every day more importantly we learn why RFID tags

don't need a battery of power source which is one of the main reasons that made RFID so popular RFID is used in many applications like your key for the door for checking

products and libraries and shops for supply change management for colgate system and many more RFID stands for radio frequency identification but what

made RFID so popular RFID could solve one of the most challenging things in electronics devices which is power source you see every electronic device

needs power and if it is a portable device like your laptop or your cell phone you need to have a battery to provide the energy for the operation of the device and these batteries can be

bulky and heavy and you will need to recharge them or change them every now and then but what if what if we can send the power to the device whenever it needs it

is it possible yes it is if we put two cords beside each other and pass the AC current through one of them then it will induce some current in the other coil

through the magnetic field coupling and the device can use this current to charge a capacitor and work without the battery of course this power will not be high enough to turn on a screen or move

a motor but it is sufficient enough for reading some data from the device and that is what made RFID so popular that we don't need to have a battery on the

device anymore well this is passive RFID and we also have active RFID switch do have a battery but I think these passive firefighters made them very popular so

an RFID system has a reader which we can see on the left and a tag or transponder which we can see on the right now let's see what is inside this tag and how it

is designed the tags have a coil or antenna and a low-power chip that can save some ideal data and send them back to the reader whenever needed in these pictures you can see the inside of the

RFID tag or card where the antenna sits on the outside and the low-power chip is on the inside now let's go and see how to design this chip so which blocks do

you think we need to have for this chip of course we need to have the power you need speech can rectify and regulate the RF signal sent to the coil what else do we need we need a controller unit with

some memory to record the data and ID this memory can be simple wrong but in many cases we need to be able to write new data to the tach like you add some

money to your canteen key right that's why we need to have an EPR what else do we need we need the transmitter you need of course to send the data back to the reader and as we discussed we also need

to write some data to the chip so we need to receive a block as well so these are the blocks that we need to implement for RFID chip let's start by the transmitter block because there is a

very intelligent idea there that I want to share so we mentioned that the power we sent to the tag is good enough for transmitting some data so you may think that perhaps we should have a transmitter to generate the RF signal

and send it to the reader however the RF transmission can be quite power hungry you need to have oscillators to generate the carrier frequency and you need to modulate the

signal to derive the antenna this antenna is usually a very low impedance load and if you want to have a transmitter it will immediately aim to the capacitor so they came with this

idea and said what if we do not transmit any RF signal then how do we transmit the data here's the idea the reader is sending the RF signal to the tag right

we can actually put a switch across the coil in the tag and whenever we have a binary bound data we close the switch and when we have a zero we open it so if

two coins have a coupled magnetic field when we short one of them it changes the inductance in the other cord and if you have RF signal on the first coil it will attenuate the signal there and the

reader can use this information to see when the coil in the tag was shorted this way we can send the information without actually sending any RF signal from tag to the reader they call it back

scatter modulation however the change in the signal of reader would be very low at the range of one - 1000 of the actual RF signal so this change is very susceptible to noise

that's why they use some other modulation like frequency shift keying or phase shift keying to improve the noise rejection in these modulations we still change the amplitude of the source

signal by switching the coil in the tank but now for example for frequency shifting we say if we keep 4 cycle off and 4 cycle on then the data is 0 and if

we keep 5 cycle off and 5 cycle on then the data is 1 so this way we are coding the 0 & 1 inside the frequency or in case of phase shift keying we say when

we change the phase of the signal it can be interpreted as 1 or 0 now let's move to design of power unit as we showed we need to have a rectifier and this

rectifier saved the charge on the capacitor sometimes they also include a multiplier circuit to increase the voltage level along with the regulator after it to regulate the voltage so

let's go to the design of controller it can be easily design using logic gates but one thing I want to mention here is that we need to have an accurate clock especially if we want to do phase shift

keying or frequency shift keying for the modulation having accurate clock can be achieved by crystal oscillator and using PLL's however this is also a power-hungry plot

so they came up with another idea and they said let's use a lot of oscillator for example a ring oscillator and then we sync it with the incoming RF signal

because that incoming RF signal is generated by the reader and it has an accurate frequency so again they use the signal from reader to achieve what they

want in this case accurate clock signal now let's move to the last block on this tag IC which is the receiver the data which is sent by the reader can simply

have a amplitude shift keying modulation because we can change the amplitude from the reader as much as we want and is not highly affected by the noise anymore then in the tag we use envelope detector

to find these ups and downs in the RF signal and extract the data so that was a rather long explanation on the design of RFID tag chip

at this point I want to discuss about RFID frequencies RFID devices can have different frequencies this is the information from Wikipedia showing the

different frequencies of RFID which is low frequency high frequency ultra high frequency and super high frequency but the most common frequency band is 13

point 56 megahertz and majority of RFID tags work in this frequency the other thing we'll learn from this data is that higher frequencies provide larger

distance range for example UHF is mainly common for the applications where a large distance is required RFID devices are not interchangeable and the

frequencies are not adjustable that is because each frequency range requires its own antenna you can actually figure out the RFI the frequency of the device by looking at the antenna the low

frequency antenna has a thin copper wire that is called hundreds of turns why the high frequency antenna will have a few turns so the higher the frequency range

the shorter the antenna will be now let's talk a bit about the readers as we discussed before RFID readers are the units that transmit the power through

the RFID tag and read or write the data to the tags right there are usually stationery units therefore they can have their own power source and we have more flexibility for design in the reader for

the reader we also have an antenna and the modulator and demodulator there are single chip solutions available for example M FRC 5 to 2 from n XP is one of

the examples for 13-point 56 megahertz RFID we do in this typical schematic we can see that it modulates the signal and transmit it to the antenna and the same signal goes back to the receiver input

to detect the signal change due to the backscatter modulation this one is a low-cost rfid reader port based on that chip and is using a PCB antenna I don't

go very much in detail on how to work with it because there are many videos on YouTube about connecting this board to Arduino so in this video what I wanted to do was to explain the main concept in

rfid common cache such as Bacchus carry modulation or power harvesting and to explain how RFID actually works I hope you enjoyed this

video and see you later