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      • PCB number of layers vs Output power

        dasimon | 08/229/2017 | 07:33 AM

        Using a 2-layer PCB in the application hardware is usually preferred by customers due to cost saving purposes. Still, based on the RF output power level, unwanted radiation of top or bottom layer traces (mostly VDD or digital) can occur, which causes that the application can violate the harmonic limits of the related standards. In order to minimize the possibility of unwanted trace radiations, Silicon Labs recommends to use multilayer PCBs in the following cases:

         

        • >=16dBm output power at sub-GHz frequencies
        • >=10dBm output power at 2.4GHz

        Note that the actual recommendation depends on which standard (ETSI, FCC, ARIB, etc.) the application has to be compliant with.

         

        One can notice that not all Silicon Labs reference design follows the above listed recommendations. EZRadioPRO reference design boards are made on 2 or 4 PCB layers based on the output power, while all EZR32 and EFR32 reference design boards are using 4 or 6 PCB layers due to the complexity of the design. In the latter case, the layout routing could not be realised on a 2-layer PCB if all digital traces were intended to be used. Of course, on a custom design where the complexity of the design is much less, 2-layer PCBs can be used for EZR32 or EFR32 applications as well considering the above listed recommendations.

      • Burning hex file into Si4010 step-by-step

        tanagy | 07/195/2017 | 12:30 PM

        The basic operation flow of the NVM Programming Utility (Si4010_NVM_Burner.exe)  is as follows:

         

        1. Select the Main tab on the GUI.

        2. Select the USB adapter.

        3. Hit the Connect button to connect to the part.

        Either:

        4. Add your application code intel hex file to the User Boot section.

        5. Keep the address value as it is — first line has 0xE180 address filled automatically.

        6. Check "Run" checkbox only.

        7. Specify the new output NVM Burn File. Choose Overwrite if desired. GUI must check the file existence before running the composer since the composer always overwrites the existing output file.

        8. Hit Compose and observe the results. The gui_composer.exe is invoked behind the scenes and the NBF file gets generated.

        Or:

        4.Load existing, previously generated NVM Burn File. The Compose Map gets filled in from the file. Then go to Step 9.

        In both cases:

        9.Make sure the 6.5 V programming voltage is connected to GPIO[0] of the part. For example, slide the PROG switch on the MSC-BA4 board to the ON position.

        10. Hit Burn to burn the device. The burning process loads the NBF file in the device and uses the information in the NBF file to do the actual burning. Observe the results. The burning process stops at first error encountered.

      • RF Range Calculator

        dasimon | 05/122/2017 | 10:19 AM

        Silicon Labs provides RF range calculators for customers to help estimating the actual range of their wireless applications. Simple RF Range Calculator is available to download from the following link below.

        http://www.silabs.com/documents/public/software/RF-Range-Calculator.zip

         

        RF range depends on the following parameters:

        • Conducted TX output power: the power driven to the antenna input [dBm]
        • TX antenna gain [dBi]
        • Conducted receiver sensitivity [dBm]
        • RX antenna gain [dBi]
        • Frequency [MHz]
        • Propagation factor (depends on the environment)

        Simple RF Range Calculator

        Simple RF Range Calculator is for those customers who don’t want to deal with difficult RF questions, just simply would like to get fast and reasonable results for both outdoor and indoor environments.

         

        Key features:

        • Fast and simple while accurate
        • Built in propagation factors, based on field measurements
        • Antenna height fixed to 1 to 1.2 meters
        • Supports all the unlicensed bands and custom frequency channels as well

        Usage

        Simple RF Range Calculator provides fast and accurate result as the customer selected the frequency band and set TX and RX parameters.

         

        Simple_Range_Calc_Fig1.png

         

        Frequency bands and custom frequency channels can also be selected.

         

        Simple_Range_Calc_Fig2.png

         

        TX Output Power and RX Sensitivity need to set up based on the radio device’s actual link parameters based on the data sheet.

        If the exact antenna parameters are unknown notes at the right side can help to determine the closest values.

         

        Simple_Range_Calc_Fig3.png

        The achievable RF range depends on many other factors as well. See the following KBA article for further details on RF range factors:

        https://www.silabs.com/community/wireless/proprietary/knowledge-base.entry.html/2017/12/07/rf_range_factors-fnT1

      • Si4x6x-C2A, Si4x55-C2A startup sequence

        tanagy | 04/96/2017 | 10:32 AM

                      In the Si4x6x chips there is a timeout after POR built-in to make sure if there is no host activity (SPI comms), the chip would go back to inactive state saving energy. Inactive state is the state the chip is sitting in after POR.

                      Because of this time-out, some refinement is necessary on the recommended startup sequence of AN633, as follows:

                     

        1. Assert SDN
        2. Wait at least 10us
        3. Deassert SDN
        4. Wait at least 14ms or until GPIO1(CTS) goes  HIGH
        5. Issue the POWER_UP command over SPI (or send first line of patch if applied)

                      This first SPI transaction has to take less than 4ms (NSEL LOW time). If it cannot be guaranteed, send a shorter command (e.g. NOP) first, check CTS, then send POWER_UP or patch.

      • PCB antenna with wider bandwidth

        zovida | 04/94/2017 | 11:04 AM

        Question

        How can I make the frequency bandwidth of PCB antennas wider?

        Answer

        In some cases/applications the BW of printed antennas might not be sufficient. This article summarizes some design tricks on how to make a printed antenna wider bandwidth.

         

        - Increase the board size (e.g. GND plane in the case of monopole-type antennas). Avoid using RF modules that have smaller size than quater-wavelength. Small modules generally have poor antenna gain and narrow bandwidth (due to the high Q factor).

         

        - Increase the board thickness. Of course, it's typically limited by design.

         

        - Decrease the dielectric constant of the PCB. Select PCB material with low epsilon value. 

         

        - Use wider and/or tapered traces in the PCB antenna structure.

         

        - Do some tricks in the external antenna matching network. I.e. use more components to do the match; create resonators in the matching network. Also, see Bode-Fano, Youla matching techniques.

      • Recommended external antenna matching network

        zovida | 04/94/2017 | 10:23 AM

        A number of antenna types can inherently be matched to the desired input impedance (typically, 50-ohm single-ended) without using any external tuning component (e.g. printed inverted-F antenna). However, board size, plastic enclosures, metal shielding, and components in close proximity to the antenna can affect antenna performance. For best performance, the antenna might require tuning that can be realized by two ways:

        • Dimension changes in the antenna layout structure, or
        • Applying external tuning components.

        It is typically a preferred solution when layout modification is not required on a custom design. To accomplish this, Silicon Labs generally recommends to ensure SMD placeholders for external antenna tuning components, where the suggested external antenna matching structure is a 3-element PI network. You can achieve a good match using as a maximum of two elements (with one series and one shunt component) of the PI network. Any unknown passive impedance can get matched to 50 ohms on this PI network, since all L, C, L-C, C-L combinations can be realized on it and therefore any de-tuning effect can be compensated out.

        Note that every implementation of an antenna design might require different combinations of inductors and capacitors.

        Recommended 3-element PI network for external antenna matching purposes:

        pi_match.png

         

      • Using PART_INFO command to identify EZRadio/PRO part number

        tanagy | 04/94/2017 | 08:24 AM

        The PART and ROMID replay fields of the PART_INFO command are sufficient to identify EZRadio/PRO part number and revision according to the following table.

         

         

        Part number PART ROM_ID Revision Top marking
        Si4060-B1B 4060 3 B1B 40601B Bxxxxx
        Si4063-B1B 4063 3 B1B 44631B Bxxxxx
        Si4355-B1A 4355 3 B1A 355A Bxxx
        Si4362-B1B 4362 3 B1B 44621B Bxxxxx
        Si4438-B1C 4438 3 B1C 44381C Bxxxxx
        Si4455-B1A 4455 3 B1A 455A Bxxx
        Si4460-B1B 4460 3 B1B 44601B Bxxxxx
        Si4461-B1B 4461 3 B1B 44611B Bxxxxx
        Si4463-B1B 4463 3 B1B 44631B Bxxxxx
        Si4464-B1B 4464 3 B1B 44641B Bxxxxx
        Si4055-C2A 4055 6 C2A 055A Cxxx
        Si4060-C2A 4060 6 C2A 40602A Cxxxxx
        Si4063-C2A 4063 6 C2A 40632A Cxxxxx
        Si4355-C2A 4355 6 C2A 355A Cxxx
        Si4362-C2A 4362 6 C2A 43622A Cxxxxx
        Si4438-C2A 4438 6 C2A 44382A Cxxxxx
        Si4455-C2A 4455 6 C2A 455A Cxxx
        Si4460-C2A 4460 6 C2A 44602A Cxxxxx
        Si4461-C2A 4461 6 C2A 44612A Cxxxxx
        Si4463-C2A 4463 6 C2A 44632A Cxxxxx
        Si4467-A2A 4467 6 A2A 44672A Cxxxxx
        Si4468-A2A 4468 6 A2A 44682A Cxxxxx

         

         

         

         

         

         

         

         

         

         

         

         

         

         

         

      • Replacement for the uPG2164 DPDT RF-switch

        zovida | 09/260/2016 | 12:06 PM

        Question

        What kind of RF-switch is recommended for the replacement of the uPG2164 DPDT RF-switch used in most of reference designs?

        Answer

        The RF-switches listed below can be good alternatives to replace the uPG2164 DPDT RF-switch. These switches have approximately the same specifications/characteristics/ratings and footprint as the uPG2164.

         

        Example list of RF switches for the replacement:

        -SKY13355: http://www.skyworksinc.com/Product/809/SKY13355-374LF?IsProduct=true

        -SKY13381: http://www.skyworksinc.com/Product/847/SKY13381-374LF?IsProduct=true

        -SKY13411: http://www.skyworksinc.com/Product/1486/SKY13411-374LF?IsProduct=true

        -SKY13438: http://www.skyworksinc.com/Product/1704/SKY13438-374LF?IsProduct=true

        -CKRF2164

        -CG2164

         

        The RF switch used in the designs needs to have:
        - low insertion loss
        - high enough frequency capability
        - high isolation

        - high enough power capability

        - low harmonic re-generation, i.e. low distortion

        - small size
        etc. 

      • Selectivity

        mabuthi | 07/190/2016 | 03:27 AM

        Question

        What is the selectivity and how could it be measured?

        Answer

        Selectivity tells how many dBs above the wanted signal level the receiver can tolerate a blocker signal while still maintaining the minimum sensitivity criterion.

         

        1. Solution to measure the selectivity: Typically selectivity can be measured with two generators. One of the generators that provides the wanted signal should be set to 3 dB above the sensitivity level (measured as the power level at which the BER is 0.1%). The second generator with an unmodulated signal is used as the interferer and combined with the primary signal using a power combiner. The second generator is placed at the desired frequency offset (red arrow) and then the power is increased until the BER degrades to 0.1%.

          graph1.jpg
          A narrowband selectivity curve in the 868 MHz band is shown on the next figure below. The x axis is frequency offset from the wanted channel in MHz, the y axis is Selectivity. This value is inverted on this graph for a more intuitive perception.
          graph2.png
          From the operation of the chip it follows that there is one offset frequency where the selectivity is worse, this frequency (at the little hump on above graph), is called the image frequency. The image frequency of the chip is at 2 x IF below the actual RF frequency. For example for the nominal crystal frequency of 26.0 MHz, the image frequency of the chip is at 2 x IF=812.5 kHz (2 x 406.25 kHz = 812.5 kHz) below the actual RF frequency.
          Let’s return to the first figure. The offset frequency –the big red arrow- generates a not wanted signal inband. The little red arrow represents this signal.

          graph3.jpg
          In order to receive the desired signal when the interferer is present, the desired signal must typically be 8–10 dB higher than the interferer. This is the co-channel rejection. As it can be seen on the Figure above, rejection is the ratio of the signal strength at the image frequency (interferer) to its counterpart at the interferer.
             
        2. Solution to measure the selectivity: This method is easier than the first one, because only one generator is needed and RSSI values need to be read back from the chip. The RSSI is measured continuously while the chip is in RX mode. The RSSI value represents the moving average of the signal strength.
          On the next figure two selectivity curves are shown in the 868 MHz band, which were measured with the two different ways on the same board. The red curve represents the RSSI measurements.

          graph4.png
          As it can be seen on the figure, that there is a constant offset between the two curves. The explanation is, that the RSSI curve represents the rejection and not the selectivity. The RSSI method is only recommended to be used around the adjacent channels and at the image, because the RSSI has a minimum noise level, which is typically too high for measuring accurately at further out offsets.
      • Recommended routing technique for more-layer RF designs

        zovida | 05/152/2016 | 09:10 AM

        Question

        How should I route the traces on more-layer RF designs for optimal performance?

        Answer

        In order to achieve the possible best RF radiated performance the followings are suggested for more-layer RF board designs:

        - Top Layer: Components and short traces. Top layer should use as large and continuous GND plane metallization as possible (with many stitching GND vias) on the entire PCB.

        - 1st inner layer: GND plane and traces if necessary. The most important rule is to keep the GND pour metallization unbroken beneath the RF areas (between the antenna, matching network and RF chip). Traces can be routed under the non-RF areas and use GND pour where possible.

        - 2nd, 3rd... inner layers: Traces. VDD and all other traces are suggested to be routed on these layers. Use GND pour where possible.   

        - Bottom Layer: GND plane. Use as large and continuous GND plane as possible. Do not route traces on this layer, just if it is necessary, e.g. short connection traces to connectors.