 Welcome to this presentation on NFC RFID Readers. In this module, we'll review a basic reader system. We'll look at the various input and output signals and components that surround our readers. We'll also describe why these components are needed and how they operate. Here we see a basic NFC reader system that consists of an MCU and an NFC Reader IC. Commands and payloads are sent via I2C or SPI from the MCU to the reader. The reader formats the data into either NFC type A, NFC type B, NFC type V, card emulation, or peer-to-peer. It then modulates the data, which creates a magnetic field in the loop antenna. The magnetic field is coupled to the loop antenna on the tag, allowing the modulated data to pass to the tag establishing communication. In addition to an MCU, a reader also requires additional components for proper operation. Here we see the building blocks of the output circuit. They consist of an EMC filter, a matching network, a receiver attenuator, and finally the antenna. Each of these blocks are critical to ensure peak RF performance and outstanding signal integrity. In the next few slides, we'll look at each of these blocks in more detail. Since an NFC reader operates at 13.56 MHz, well below the typical measured FCC radiated testing limits, the question is frequently asked, why do we need an EMC filter? Very simply put, the RF output of the reader is a series of trapezoidal pulses. The edges of these pulses create harmonics that appear in the spectrum above 30 MHz. It's for this reason that the filter is implemented. As stated earlier, the EMC filter reduces the higher harmonics from the RF output signal. In order to attenuate these higher frequencies, a two-pole low-pass filter, consisting of an inductor and a capacitor, is placed at the differential outputs of the reader. The cutoff of this filter is set at approximately 13.56 MHz. It's very important that this filter be placed as close as possible to the output of the reader. If it is not, the traces between the output of the reader and the filter may unintentionally radiate unwanted frequencies causing problems with FCC certification. Another key block of the output circuit is the receiver attenuator. For the reader IC to work properly, the receiver must be monitoring all activity on the antenna. It's fairly common on some reader applications where the output voltage swing on the antenna can be in excess of 50 volts peak to peak. This output swing is influenced by the Q factor of the antenna. The maximum receiver input specification for the ST25R3911B and the ST25R3916 is approximately 3 volts. In order to reduce the antenna voltage to an acceptable level, a divider is needed. This is implemented with a simple capacitive divider. The antenna creates the magnetic field and transmits and receives the data between the reader and the tag. Antennas are generally custom designed primarily because size requirements vary greatly among reader implementations. Despite this, the most common implementations are seen here. Typically in a proof of concept stage, it's very common to use a wire wound antenna to get initial performance parameters. This is because they are relatively easy to implement and can be changed relatively quickly to evaluate various antenna sizes. When a product moves to production, a customer will move to either a PCB antenna, either rigid or flex, depending on space requirements, or a ferrite antenna if the antenna will be in close proximity to metal. In an NFC system, the antennas are simply inductive loops or coils. Therefore, the electrical model for the antenna is a coil. The model parameters that are important are the inductance, the serial DC resistance, the parallel resistance, and the working frequency, which in this case is 13.56 MHz. Antenna parameters can be measured with a vector network analyzer. The measured parameters are dependent on the physical characteristics of the antenna. Therefore, the measured parameters can be modified by changing the physical characteristics of the antenna. For instance, to increase the Q factor, thus potentially increasing read range, one could modify the antenna by increasing the trace width or gap width. Likewise, if one wanted to decrease the inductance of the antenna to potentially use a higher value parallel capacitor, one could decrease the size of the antenna. It's important to know that external environmental conditions can also affect antenna parameters, such as metal in close proximity to the antenna. If the environmental conditions are known, it is important to measure the antenna parameters in the environment in which it will be operating. The final component in the output circuit is the matching network. Its primary functions are to create a resonant circuit with the antenna at 13.56 MHz, set the matching impedance, which controls output power and current consumption, and sets the Q factor for the system. It's important to note that the Q factor of the system will always be lower than the antenna Q factor. So when designing an antenna, a higher Q is generally more desirable. In order to determine the proper impedance match in Q, one must know the system design requirements. These would include what protocols will be supported, what bit rates, what read range, and current consumption. Typically, optimization requires a trade-off between current consumption and read range. As mentioned before, the impedance match will determine the output power and current consumption. Thus, if you wanted to reduce power consumption, you would match to a higher impedance, reducing the current to the output drivers. The opposite would also be true. For more output power, the impedance match would have to be reduced, providing more current to the output drivers. The Q is adjusted to change the sensitivity of the system, as well as to accommodate the required bit rate. A higher Q results in more sensitivity, but at the cost of allowing lower bit rates. We've stated that the matching network controls the resonance of the antenna and the impedance match. It also has to compensate for the effects of the EMC filter and the receiver attenuator. If either of these blocks change, then the matching network would have to change to compensate. So in the big picture of things, the matching circuit encompasses the EMC filter and the receiver attenuator, as indicated in the dashed lines in the block diagram. As such, all of these blocks have to be calculated and evaluated together. Changing any one of these component values will likely require rematching. Here we see the actual components that make up the matching network for the differential output. LEMC and CEMC 1 and 2 create the two-pole EMC filter. CS1 and CS2 adjust the impedance match. CP1 and CP2 control the resonance. C1 through 4 adjust the receiver input. And RQ1 and RQ2 adjust the Q of the system. While I casually mentioned what each of the components does in the circuit, they are all mutually dependent, meaning that if one value is changed, the others will likely have to be adjusted. Thank you for viewing this presentation.