Proprietary Knowledge Base

    Publish
     
      • EZradioPRO PA ramp induced spectral splatter mitigation techniques

        zopapp | 05/138/2017 | 04:42 AM

        What is causing spectral splatter?

         

        Let’s have a look at this concept through a simple example. Suppose you transmit a pure CW signal. Your spectrum will look like a single tone at the carrier frequency. When you start switching this CW tone on and off with a square wave pattern the spectrum of the square wave pattern will be convolved with the CW spectrum resulting in a sinx/x like overall spectrum profile around the carrier. If the switching is not part of the core modulation (in this example a CW tone) than the increased spectral components induced by switching are not desired and referred to as spectral splatter.

         

        If you substitute the CW tone in above example with an arbitrary modulated signal and the switching pattern with an RF packet start / stop ramp you arrive at real example that will behave the same way as the simplified case.

         

        How do we control spectral splatter?

         

        Spectral splatter can be kept at bay by controlling the ramp profiles in time domain at the beginning and end of the packets. As a rule of thumb the longer the ramp the narrower its splatter spectrum. The goal here is to keep the splatter spectrum within the modulated signal’s own spectrum so no out of band splatter occurs at all. Although this cannot be achieved for all modulating formats on Si446x there are turning knobs the issue can be mitigated with.

         

        What are the knobs on mitigating spectral splatter on Si446x?

         

        1) The first knob is field PA_TC in API property PA_TC. This field directly controls the ramp time on the PA. WDS configures this filed to a value of 0x1D by default which leaves two notches until the maximum ramp time is achieved at 0x1F. If a loner ramp is needed adjust this field manually to one of the higher values.

         

        Note1: If you have increased this value you may want to readjust API property PA_RAMP_DOWN_DELAY to prevent the PA from shutting off before the ramp down has finished. Increase this value if you see issues at ramp down.

         

        Note2: This scheme applies to all ramp up/down events in OOK modulation.

         

        2) On Si446x revC2A (and Si4467/68 revA2A) a digital power ramping feature was introduced that sequentially steps through PA_POWER_LVL values (from min to max with a configurable step size) with a configurable dwell time on each of these steps. Much longer ramp times can be achieved with this approach.

         

        You can enable this feature by setting field DIG_PWR_SEQ in API property PA_MODE. You can configure the dwell time and the step size in API property PA_DIG_PWR_SEQ_CONFIG.

         

        Note that with this method the built-in PA ramp (discussed at (1)) is not applied between the steps only at the 1st step at minimum power level.

         

        The digital power ramp feature has a bug that is not fixed with released FW patches: the power ramp only takes effect at ramp up but does not take effect at ramp down.

         

        There is a SW workaround to the issue:

         

        After POWER_UP 

        1) Do the following SPI write 0xF1474B00. Wait for CTS.
        2) Make a transition to SLEEP state
        3) Make a transition back to READY state

         

         

      • Do I have to use RAIL to access and configure the transceiver for my proprietary protocol on EFR32 devices?

        Siliconlabs | 05/124/2017 | 11:05 AM

        Question

        Do I have to use RAIL to access and configure the transceiver for my proprietary protocol on EFR32 devices?

        Answer

        Yes, RAIL and Radio Configurator tool in Simplicity Studio are the currently available means to configure and access the radio on EFR32 devices. Over the past decades we have seen an evolution in software programming from assembly code to C programming and nowadays to object oriented programming like Java, Python or C++. This was done to facilitate development of bigger and more complex software and also simplify the overall programming experience by allowing engineers to focus on their designs. On the wireless connectivity side, the integrated transceivers are also getting more complex due to multiband-multiprotocol operation in resource constrained environments. Over the last many generation of our products we have also seen an exponential growth in the MCU and transceiver complexity that has increased the customer’s time to market. The multiple optimization vectors make it difficult for an individual customer to optimally configure the transceiver within the SOC especially for proprietary wireless protocols. Furthermore each setting and configuration must be tested to ensure proper performance as part of the SOC. To make the product easier to use we abstract the radio through an interface layer called the Radio Abstraction Interface Layer (RAIL). This improves our customer’s time to market, ensures code portability and guarantees the best possible performance for given configurations. Periodically there is a configuration that hasn’t been created for the device, the configuration list is constantly evolving. In that case you can contact your local FAE or customer apps to request a specific configuration be added.

      • 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