 Hello, this video is the last part of a series on practical RF impedance matching and filtering of the STM32WL. In this part, we focus on the Receiver Matching Network and Balloon. As mentioned in the first part of this series, there are several ways how to do this task that differ in complexity. In this example, we show the simplest method based on a reusing an existing STM32WL design. It should be enough for most of designs. The main steps of this method are Using the reference layout of the Receiver section as much as possible Using Receiver Component Values as in the reference design The Component Values can be fine-tuned if needed. Fine-tuning may be needed due to differences in the layout, RF switch, component types, etc. Fine-tuning is based on measurement of Receiver Sensitivity, Receiver Standing Wave Ratio and Current Consumption. These points are described in more detail in the following slides. There are several designs which can be reused. Some examples are here. Each board has a bit different configuration. There are boards for BGA or QFN package for two or four layers, etc. The Receiver Component Values were tuned for each particular board. The Values can be reused as initial values and the new design. Design files and BOM can be downloaded on st.com. In this example, we use STN32WL nuclear board. Here is the schematic of the Receiver part of the STN32WL nuclear board. We can see Balloon Light and Matching Network, the RF switch and the DC block, the Antenna Matching Network and the SMA connector. The Balloon Light circuit transforms the single-ended signal to differential. As we mentioned in the previous part of this series, strong harmonics from the transmitter may couple to the Receiver part through the PCB. This capacitor can help attenuate these harmonics. The recommended values for the Receiver part on this board are as follows. We use these values on the original board, so fine-tuning is not needed. The Antenna Matching Network uses the values that we calculated in the previous section about the transmitter. The PCB layout of the Receiver path looks like this. We can see differential inputs of the Receiver and differential transmission line, Balloon Light and Matching Network, capacitor which can attenuate coupled harmonics from the transmitter part, RF switch, DC block, Antenna Matching Network and the SMA connector. Impedance of the single-ended RF line is 50 ohms. Impedance of the differential RF line is 100 ohms. Length of the differential RF line has impact to the Balloon Light components. If the length is different, the values may need to be fine-tuned. In this picture is highlighted the Receiver path on the tested board. From differential pins through the Balloon Light circuit, RF switch and the Antenna Matching to the SMA connector. The AT Slave can be used also for testing of the Receiver. During the measurement, we need to set the RF switch to the Receiver mode and set the STM32WL to the Receiver mode as well. Here are the commands which can be used. For configuration, we can use the same command as we use for the transmitter. For sensitivity measurements, we need to set parameters of the modulated signal. If we want to only turn on the Receiver, no special setting is needed. We can use default values. The ATTRX command switches the STM32WL into the Receiving mode. The parameter is number of packets, which will be received. This parameter is used for calculation of the packet error rate. Here is the example of this command. 10 packets were being received. There was noted signal on the SMA, so the calculated packet error rate is 100%. The most important measurement is the Receiver sensitivity measurement. Good Receiver sensitivity means that the button light circuit and the matching are set correctly. The Receiver sensitivity depends on the modulation and its parameters. The datasheet specifies some sensitivities. They can be used as references for other measurements. Sensitivity measurement is quite complex. The simplified variant of sensitivity measurement is shown in the separated video of this series, which is named as basic RF measurements. On our test board, this sensitivity was measured. Lura modulation with these parameters was used. If we compare this value with the reference one in the datasheet, our Receiver path is set correctly. The standing wave ratio measurement indicates how well is the Receiver path matched. Good value is typically below 1.5. The measurement of the standing wave is quite easy. The vector network analyzer is connected directly to the SMA connector of the board. The STM32WL is set to Receiver mode. The RF input power of the Receiver should be below 0 dBm. In our example, the power from the VNA is minus 30 dBm. Here is measured standing wave ratio of our board. It is around 1.5 dBm in the whole band. The exact values are listed here. The last thing to check is that the current in Receiver mode is within the expected range. Typical currents for some cases are in the datasheet. The main difference is in the SNPS and LDO mode. The variants with boosted receiver have slightly bigger value. On our test board, the current is measured at the same point as we used for the transmitter. It is marked as IRF. Our measured current is about 5.5 mA, which is expected value. The optimum values for a particular design may differ from the values used on the reference boards. In this case, the reference values can be considered as initial values which can be fine-tuned. Maximum values for the particular board are usually around these initial values. This is valid if the Receiver part layout is similar to the reference. Typically, these two capacitors are slightly modified. One sets the matching, the second phase and amplitude of the differential signal. It's recommended to change only one value at a time to see the impact. Changing one capacitor may affect the other, several steps may be needed. After each change, the impact of the change must be verified. The most important is the sensitivity. The standing wave ratio may help with tuning. We can see where the matching is better and where worse. Let's summarize the Receiver part matching. Matching of the receiver may be time-consuming. To speed up the process, the recommended way is to reuse the existing layout and boom of reference boards. The boom values can be used as initial values for new design. These initial values can be fine-tuned if needed. If the PCB layout is similar, the optimum values are usually around the initial values. Typical measurements of the Receiver parts are sensitivity, standing wave ratio and current consumption measurements. Thank you for your attention.