 Let's move on to design tips so you can start designing your own boards. So what we'll do is we'll look at antenna design and matching, we'll look at power consumption, and then look over some PC board layout recommendations. Antenna design and matching is typically where hardware engineers spend about 90% of their times during a design cycle. So it starts with a requirement specification that specifies things like the physical parameters of the antenna, so the size and the geometry, the technology, which is basically what the antenna will be made of, the expected modes of operation, whether it'll be polling continuously, whether it'll be in a low power wake-up state, the expected power consumption, and the expected read range. And normally these are the two trade-offs when designing an NFC system, is power consumption versus read range. You also have to identify what technologies you'll support, whether it be 14443, type A, type B, 15693, active peer-to-peer, all this has to be taken into consideration. And also the source of the power for the system, whether it be a battery or DC to DC converter, this is also important information. And then finally other constraints such as environmental conditions or possibly the proximity to metal of the antenna. So once these parameters are determined, we go to antenna design. And antenna design you can use an online tool that ST has, or very simply for most of the readers we provide, we suggest a two-turn antenna with an inductance value somewhere between 200 nanohenrys and 2 microhenrys. From there you would measure the parameters of the antenna after you've designed it, and then you would use that to simulate and calculate the matching components for the circuit. From there you would go to design verification where you would measure things like read range, impedance matching, power consumption, wave shapes, and any ISO or NFC form or EMV co-testing that's required. As previously mentioned, ST has its e-design suite, which is a simple antenna calculator by putting in the parameters for the geometry of your antenna as well as the conductor and substrate, it will calculate the inductance of the antenna at 13.56 megahertz. So this can be used with very simple shaped antennas. There are also third-party tools available if you want to import your own Gerbers. After designing our antenna, we'll need to measure parameters on the antenna in order to calculate the matching circuit. So if we look at our Smith chart here, we would measure from 1 megahertz up to the self-resonant frequency of the antenna. From there, we would measure the following parameters, which is the resistance at 1 megahertz, in this case it's 200 milliohms, the inductance at 1 megahertz, which turns out to be 231 nanohenrys, the self-resonant frequency, which is characterized by the crossing of the real axis here, at 539 megahertz, and finally the parallel resistance at self-resonant frequency, which is 6.4 kohms. The next step is to take the measured parameters and input them into the 3911B antenna matching tool, which is available online. Here we would put the antenna values that we measured. We would then select a preset, either EMVCO, VHBR, or general purpose. And what this preset does is set the cutoff frequency of the EMC filter, the target matching impedance, and the target antenna queue. These values can also be overridden if need be. There's also an area here where you can put in the DC resistance of the inductors that are used in the EMC filter. We would then hit calculate matching values, and the matching circuit would be populated with values. From here we would save and simulate the circuit, and this would bring up QWUX, which is a simulation program. The QWUX simulation will produce three models. An S-parameter model, which will provide the Smith chart and matching impedance. A transient model, which will produce the antenna voltage and the RFI input voltage, as well as an AC model, which will give you AC results. It's important to note that the circuit calculator does not always calculate standard capacitive values. So if this is the case, you have to go into the QWUX simulation and change those to standard values, and then re-simulate. There are several ways to reduce power consumption on the 3911B. The first and foremost is the matching impedance. So matching at higher impedance will reduce the power consumption of the device. You can also use register 27, which defines the output impedance of the driver stage. So these are eight binary weighted drivers that can be adjusted via register settings. However, most of the time this is used to reduce overshoots by the matching, and this can be seen in the simulation. You can also do a dynamic polling cycle where it reduces the number of times that the reader pulls. This will reduce power consumption as well. And finally, you can adjust the regulator setting to reduce power. Be careful though, register 27 and adjusting the regulator settings typically means more power consumption in the device, which means the device may get hot. So for PC board layout, we would recommend that the EMC filter be placed as close as possible to the 3911. This is so that the harmonics generated from the 13.56 MHz signal don't radiate throughout the board. The EMC inductors are typically wire wound inductors, and as such we recommend that they are placed 90 degrees from each other, and this is so that you don't create a mutual inductance between the two inductors. We also recommend that the RFI and RFO lines are routed symmetrically and away from each other. Make sure there's no long traces between the LC filter and the remaining matching components. We also recommend that the decoupling capacitors are placed as close as possible to the chip. So these are typically a 2.2 microfarad and a 10 nanofarad. In addition, we always recommend a thermal pad underneath the device, especially when driving high amounts of power. And finally, there's a wide variety of application notes available online, and these cover topics like PC board layout recommendations, antenna design, EMV cookbook, automatic antenna tuning, and wake up.