 Hello, and welcome to the STN32WB RF overview session. We will deal with two topics, what is RF and STN32WB RF overview. Now, let's take a closer look at the STN32WB series of ultra-low-power Bluetooth low-energy and IEEE 82.15.4 thread microcontrollers. These are four major points that characterize the STN32WB series. It's the leader in ultra-low-power microcontrollers and in boosting performance. ST has built a new architecture to reach best in class ultra-low-power figures thanks to its high flexibility. Moreover, the STN32WB's performance shatters the competition in ultra-low-power world. It delivers 80D MIPS based on its ARM Cortex-M4 core with a floating-point unit and ST's adaptive real-time memory accelerator at 64 MHz. Innovation lead chip to address a large IoT market range, several innovations on its architecture are implemented and smart peripherals are embedded. Innovation and safety features 1MB of flash memory and 256KB of SRAM along with safety and security features, smart and numerous peripherals, advanced and low-power analog circuits in small packages. Long-term and advantages investment This new series of STN32 microcontrollers benefits from IP compatibility of the STN32WB family and its ecosystem. Although you will not become an RF expert after this introduction, you will better understand vocabulary and constraints usually associated with RF by demystified. What will give this session to you? Gives you the necessary definition, illustrating what a radio system is on a typical 2.55 gigahertz band, describing the different system on blocks necessary to design a wireless link and giving some hints on how to define a radio system based on one's constraints. Radio frequency communication has a long story, more than one century. From a theoretical aspect, first beginning of 19th century, we can name Gauss, Ampere, Faraday, Maxwell and others. To an experimental aspect, at the beginning of 20th century, Tesla Hertz, Marconi. Here are several milestones. In 1890s, first wireless telegraphy by Tesla. In 1900s, first transatlantic communication by Marconi. In 1907, first appearance of the word radio. In 1920s, first AM broadcast stations. In 1940s, first FM broadcast stations. In 1960s, first satellite communication. In 1980s, first ground based RF communications. In 1985s, first ISM unlicensed spectrum FCC. Let's start with mandatory definition of RF. A radio communication is a wireless transmission of a signal through the air using electromagnetic radiation at a certain frequency. The complete radio system is made of a transmitter that emits the signal, a receiver that gets the signal, an antenna on both sides. It converts the electrical signal into electromagnetic waves and vice versa. A component embedding both transmitter and receiving block is called a transceiver. RF system can be classified depending on its ability to provide unidirectional or bidirectional link. The first is simplex RF system. It is only one way communication from transmitter to receiver. These are common communication devices as FM radio, TV, or door opener. The second is half duplex RF system. It is the two way communication between end devices which can both transmit and receive, but not simultaneously. The devices use TDMA, time division multiple access. For example, walkie-talkie. The third is full duplex RF system. It is the communication between end devices which can both transmit and receive simultaneously. Applies to frequency division duplex system. For example, cellular phones. Mandatory units. Due to wide power dynamics evolved in RF, linear expression of power is unpractical. In RF is main unit the decibel. In RF is main unit the decibel. It is logarithmic unit that expresses the magnitude of a power ratio related to a reference value. Power level is expressed as p is equal to 10 multiplied by logarithm p1 divided by p0. When the power level is expressed in dB then p1 is power to be measured in watts and p0 is reference power in this case 1 watt. When the power level is expressed in dBm then p1 is power to be measured in milliwatts and p0 is reference power 1 milliwatts. Here are several conversions. 1 milliwatts is 0 dBm, 10 milliwatts are 10 dBm, 100 milliwatts are 20 dBm. 1 watt is 0 dBm and it is 30 dBm. 1 watt is 0 dB and it is 30 dBm. When the power level is expressed in dBc then p0 is carrier power in dB. The RF spectrum. Radio spectrum is limited and shared resource. A few bands are worldwide. The radio spectrum is the part of the electromagnetic spectrum. The radio spectrum is considered from 30 Hz to 300 GHz. To prevent interference between users of the spectrum, generation of the waves is strictly regulated by national laws and coordinated by the International Telecommunication Union. Different parts of the radio spectrum are allocated by the ITU for different technologies. In some cases parts of the radio spectrum are sold or licensed to operators or private radio transmission services. For example TVs or GSM operators. Because of increasing the number of users the radio spectrum has become congested. There is a need to utilize it more effectively by modern telecommunication technologies. The RF blocks. Generic RF communication contains transmitter radio channel receiver. The source is the message we want to send followed by signal encoder and RF modulator. It is modulated by the carrier wave to appropriate carrier frequency. At the receiver side there is a down converter that converts the radio spectrum to intermediate frequency with help of the carrier wave. It is followed by the IF modulator and signal decoder that recovers the message. We can shortly describe the radio integrated circuit as SDN32WV is. It contains both main parts the transmitter and the receiver. Also it embeds the synthesizer of frequency. It needs the reference oscillator that could be covered by crystal RF transmitter. Generic RF communication contains transmitter radio channel receiver. The transmitter's goal is to output a signal at specific frequency with a specific power. It performs up conversion and amplification and driving gain using an adequate modulation scheme. Using an adequate modulation scheme it injures a modulator while respecting our standard not to interfere with other radio systems. When building a transmitter one must care of maximum output power, the maximum output power provided at given load impedance transmits spectrum mask. The power must remain contained into a specified bandwidth at certain frequency offsets relative to the total carrier power. Spurious emission. It is emission outside the necessary bandwidth. Harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products. Modulation. Users data cannot be directly sent to the antenna because frequency of this data is quite low and effective antenna should be very large. Therefore carrier signal is used. Frequency of the carrier signal is much higher than the frequency of data. Modulator modulates the carrier signal with users data. Parameters of the carrier which can be changed. There are many types of modulation scheme. Among the basic ones include amplitude shift keying ASK, frequency shift keying FSK, phase shift keying and combinations for example quadrature amplitude modulation QAM. Here are the examples of modulations. To ASK, two states amplitude shift keying is a form of amplitude modulation that represents binary digital data in the amplitude of a carrier signal. To FSK, two states frequency shift keying is a frequency modulation scheme in which binary digital information is transmitted through discrete frequency changes of a carrier signal. In BLE is used the GFSK Gaussian frequency shift keying. It is the FSK where data are filtered with Gaussian filter at first. Here you can see the example of real BLE RF signal as we can measure by the spectrum analyzer. The pictures show us carrier frequency at 2.45 GHz with output power minus 30 dBm. The left picture is unmodulated signal, carrier signal. The right picture is modulated carrier with pseudo random binary sequence with length of 15. The receiver. The goal of receiver is to receive and decode a weak signal in the presence or not of external interferences. When building the receiver we must take care of. Sensitivity is the lowest input power with acceptable link quality. The sensitivity level is the antenna power at which the percentage of bits or packets not received reach a standard desired value dependent on modulation scheme, data rate and channel bandwidth, packet error rate or bit error rate. Dynamic range is the input power range which results in a correct demodulated signal. Selectivity performance is a measure of the capability of the receiver to demodulate a wanted signal in the presence of an unwanted modulated signal in the adjacent channel or in the same channel. Blocking performance is a measure of the capability of the receiver to demodulate a wanted signal in the presence of unmodulated carriers as harmonics and spurious signals in the spectrum. Here are some examples of selectivity performance for adjacent channel. It is interferos signal located next to wanted signal and co-channel where interferos signal has the same frequency as wanted signal. The blocking performance is immunity to unmodulated signal in proximity of wanted signal. The SDN32WB transceiver. Here are some details about RF transceiver inside the SDN32WB. The RF part of SDN32WB IoT radio interface consists of transmitter, receiver, crystal oscillator, internal matching network and pre-filter, mixers, intermediate frequency stages with band pass filters, digital interface and dedicated power management. Now we focus on crystal. Crystal is the critical external component associated with internal oscillator. It provides the reference frequency for the whole SDN32WB. Crystal oscillator provides the reference frequency for local oscillator and the carrier frequency. It uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal at a certain frequency. Simple crystal oscillators show a great variation of frequency versus temperature and aging. There are further possibilities to generate more stabilized oscillator signal. TCXO temperature controlled oscillator adjusts the frequency to compensate deviation versus temperature variations. VCXO voltage control crystal oscillator adjusts the frequency thanks to an external voltage line. VCXO voltage controlled and temperature compensated crystal oscillator is adjustable in both voltage and temperature range. What has to fulfill the crystal for SDN32WB? 32 MHz crystal. Its stability and initial tolerance should be better than plus minus 50 ppm internal crystal trim through register programmation can be useful to compensate for temperature error and rift. Balloon and harmonic filters are very usual external components in radios. Balloon, it converts a balanced signal to an unbalanced one. In other words, from differential to single-ended. Matching network. Matching network. It provides impedance transformation in order to maximize, transmit power and receive sensitivity. Filter. It aims to pass the wanted frequency band and reject the unwanted ones. For example, harmonics. Requirements are reduced in SDN32WB thanks to internal pre-filtering. If all subsystems in RF system have the same impedance, the power transfer from the source to a load is the best. The most common impedance is 50 ohm. Let's show the ideal case. All subsystems and interconnections have the same impedance. Then there are no impedance mismatch losses. Maximum power is transferred to the load. Here is the real case. Real impedances are usually around 50 ohm. Real impedances are frequency dependent. Usually denoted as complex number at particular frequency. For example, 49-j5 ohm at center frequency 2.45 GHz. If there is the impedance mismatch, part of the power is reflected back to the source and less power is delivered to the load. To get the best performance with real impedances of components, the impedance matching circuit is needed. It transformates impedances between two ports. If interconnected input and output impedances are complex conjugated, then there is no power reflection. Correct impedance matching. In transmitter path increases output power into the antenna. In receiver path increases sensitivity of the receiver. Now we focus on Smith chart. It is the most common diagram in RF. It represents the graphical tool to visualize impedance, reflection coefficient, etc. All impedance values in the diagram are normalized in most cases to 50 ohm. It is useful tool for impedance matching, forms of Smith chart. Printed on paper, an interactive application, a lot of online application available on the web for free. More details is mentioned in ST application known AN 5165. Tutorials are available freely on the web. Smith chart variance. Impedance. Z shows a resistance R and reactance X. Better for serial impedance connection. Admittance Y shows conductance G and susceptance B. Relation with Z, Y equals to 1 divided by Z. Better for parallel admittance connection. Both variants in one graph is also possible. It is quite common variant. Useful if both serial and parallel components are used. For example matching. The upper part of the chart is inductive. The lower part is capacitive. In impedance variant the circles are with constant resistivity. Curves are with constant reactance. In admittance variant the circles are with constant conductance. Curves are with constant susceptance. Important points in Smith chart. Short. The point where impedance equals to 0 ohm is on the edge on the left. Open. The point where impedance equals to infinity ohm is on the edge of the right. Match. The point where impedance equals to relative value in this case 50 ohm is in the middle. Shapes in the chart. Circles. All circles means constant resistivity or conductance in admittance variant. Curves. All curves means constant reactance or susceptance in admittance variant. Again top curves reports to inductive part. Bottom curves capacitive part. Now we show how the impedance moves in Smith chart. Consider serial connection Z equals to resistance plus J reactance. Change of R moves Z point along the curve. Higher R, right. Lower R, left. Change of Jx moves Z point along the circle. Higher L, up. Lower C, down. Similarly in parallel connection Y equals to conductance plus J susceptance. Change of G moves Y point along the curve. Higher G, left. Lower G, right. Change of Jb moves Y point along the circle. Lower L, up. Higher C, down. Impedances in the Smith chart. Z1 is equal to 50. Pure resistance. Z2 is equal to 50 plus J20. Resistance with serial inductance. Z3 is equal to 50 minus J50. Resistance with serial capacitance. Z4 is equal to 30 plus J20. It is resistance with serial inductance. Compare. In cases Z1, Z2, Z3 resistance is constant because points are still on the same circle. R is equal to 50. In cases Z2 and Z4 reactance is constant because points are still on the same curve. X is equal to J20. Impedance matching. Let's have an input impedance Z1 is equal to 88 plus J33. Target impedance Z is 50. There are a lot of possible variants how to get from Z1 to Z. In this example, parallel inductor L moves Z1 to the circle with constant resistance 50. Serial capacitor moves the impedance to the center of the Smith chart where Z is pure 50. Matching is frequency dependent. For example, at frequency 1 gigahertz, inductance is 25 nano Henry, capacitance is 3.2 picofarad. At other frequencies, values will be different. RF line. What is RF line and why is needed? RF lines are PCB traces among RF components. Arbitrary PCB trace cannot be used in RF. It has some parasitic inductance and capacitance which become significant at high frequencies and affect the trace impedance. To avoid impedance mismatch, RF line on PCB must have correct impedance, commonly 50 ohm. Impedance of RF line depends on geometrical parameters, material parameters and the frequency. There are available calculators for this purpose. Most common types of RF lining PCBs are coplanar with ground plane called GCPW and microstrip line. In the layout is marked the RF trace calculated for 2.45 gigahertz frequency and the material constants. Antina is the interface between radio and the air. Its performances greatly impacts the range. Antina role is to transform electrical signal into electromagnetic waves. This role is often underestimated but without Antina there cannot be radio link. There is no magic Antina but many types of Antina exists. Their size depends on the frequency for which they are designed but is generally close to the one of quarter of the wavelength. The lower frequency is, the bigger Antina is. For example, one quarter wavelength vertical is about 40 meters long when used on 1.8 megahertz but it is only 4 centimeters long on 1.8 gigahertz. Here are several samples of Antinas with SMA connector, chip Antina like SMD component or PCB Antinas. The picture in right example of low frequency Antina. Antina is usually a narrow band device and is not necessary omnidirectional. Antina characteristics must be carefully watched out. Resonance frequency and impedance matching. Generator 50 ohms for optimal power transfer. Impedance matching limited in terms of bandwidth and Antina cannot be an all-band Antina without excessive losses. The relation of impedance versus frequency shows the capacitive and inductive part of an Antina. Efficiency, directivity and gain. Antina directivity denoted as D is the ability of an Antina to focus energy in a particular direction when transmitting or to receive energy better from a particular direction when receiving. Antina efficiency denoted as E is the amount of energy radiated compared to the amount of energy at the input terminus of the Antina. And Antina gain denoted as G is the product E multiplied by D. It is given in reference to a standard Antina. For instance an Isotropic Antina. Below is an example of a cut of radiation pattern and its 3D representation. RF measurement equipment. The basic equipment is spectrum analyzer, vector network analyzer and signal generator. Spectrum analyzer. Displays frequency spectrum of the RF signal. Optionally can also analyze signal parameters, modulation parameters, frame content ATC, frame content etc. Then we call it as signal analyzer. Common measurements, output power, harmonics, spurious, occupied bandwidth, modulation characteristics. Vector network analyzer, VNA, measures parameters of RF components as parameters. Common measurements, impedance matching, measurement of attenuation or gain, transmission characteristics. Signal generator. Generates RF signal for example only carrier with some modulation, special test signal according standards etc. Common measurements, cut channel and adjacent channel receive solitivity, receiver blocking performance and much more. S-parameters are scattering parameters. They describe parameters of RF components. Here are S-parameters for two port components. S-11, reflection of port 1. Lower S-11, less reflection and better. S-12, power transfer from port 2 to port 1. S-21 is power transfer from port 1 to port 2. S-22, reflection of port 2. The same properties as for S-11. Examples. One port antenna at 2.4 GHz. S-11 is equal to minus 10.5 dB. Two port, for example attenuator 20 dB at 1 GHz. S-11 is equal to minus 15.8 dB. S-12 is equal to minus 20.5 dB. S-21 is equal to minus 20.5 dB and S-22 is equal to minus 16 dB. Ideal link budget is calculated using geometrical, sphere, surface considerations and line of sight hypothesis. The radial link will be valuable if and only if the input power at the receiver side is higher than its minimum sensitivity level. If not, receiver will erroneously decode the input signal and the radial link. The equation is called as Frieze equation. It expresses attenuation of the free space with isotropic antenna. Aric sensitivity must fulfill unequality below. It is relation for energy balance. Ideal link budget is affected in practice by numerous things like non-line of sight. In real life, it is difficult to correctly estimate field losses to determine the maximum allowable distance between a transmitter and a receiver. In the low part of the R spectrum, HF and lover, field losses mainly depend on solar cycle and seasonal conditions. In the high part of the R spectrum, VHF and higher, field losses mainly depend on local environment condition, where obstacles are big in comparison to wavelength. There are many phenomenons, like reflection, diffraction, scattering change, the propagation loss. It creates complicated model. Then the environmental obstacles as walls, buildings, causing multipath propagation are important cause of losses. For STN32WB that operates in the 2.45GHz band, the range is usually not depending at all on natural perturbation but to the presence of interferers, like Wi-Fi or physical obstacles like doors, chairs, human body, metal plane and so on. Due to the fact that the link budget worsened at ultra-high frequency, usual range is no more than some tens of meters. RSSI is radio strength signal indicator. The RSSI is a value expressed in DBM that represents the received power in the channel we are receiving. It is extracted from the receiver ADC plus digital channel filter. The gain of the chain is then subtracted to deduct exact power at antenna. If the gain can change, it is usually the case when an automatic gain control loop is activated. The RSSI value should automatically take into account this gain change in real time. The RSSI is useful to check the RF activity to discover if a channel is free, confirm that the RF power is high enough to have a good chance to operate with good SNR and also good bear, make a coarse estimation of the TX or RX distance. RSSI is directly readable through the BTLE or ThreadStack. The RSSI is directly available through the stack of the STN32WB. All needed calculations are done inside the chip. Value in DBM is directly available by reading register. The RSSI usually has some limited accuracy. Because the exact gain of the chain should be subtracted to calculate the RSSI, some inaccuracy exists. Gain is depending on antenna matching. Gain is depending on temperature, variations from chip to chip. Measure of the level at RX ADC output is affected by noise, especially at low RF level on antenna and linear to logarithmic conversion algorithm. Rule of tomb of RSSI accuracy is usually plus minus 2 dB. RF standards. RF standards should always apply to optimize application and minimize perturbations. RF spectrum is a limited but shares resources, requiring regulations and licensing on some bands to allow operation. In sub-gigahertz applications they use unlicensed ISM or SRD bands, but each of them are regulated locally by well-defined RF standards. Those RF standards define the minimum set of RF performances to be fulfilled to be allowed to use this frequency band. Here are the Bluetooth band ranges in several areas. Several technology available depending on data rate and range. Different technologies utilize different modulation schemes, different power, bandwidth and so. Therefore, they can transmit various bow traits. They are also dedicated to different distances. Okay, thanks for watching, goodbye.