1 2 Previous Next 18 Replies Latest reply on Jul 25, 2016 12:46 AM by UdSc_2195666

    BLE radio frequencies incorrect (BCM20736S)

    UdSc_2195666

      Hi all,

       

      while testing our application based on the BCM20736S it turns out that in some cases it is impossible to connect to a few of our devices after a certain runtime. The advertisements are being sent out, but no master-device is able to receive it. With our spectrum analyzer we found out that the frequencies of the advertising channels are shifted, so the BCM20736S sends out its advertisements on wrong frequencies and no end device is able to establish a connection.

       

      Has anyone seen similar issues? If yes, how can we solve this problem?

       

      With best regards,

       

      Udo

        • 1. Re: BLE radio frequencies incorrect (BCM20736S)
          BoonT_56

          What do you exactly mean by wrong frequencies?

           

          In an advertising event, the device will advertise once in 2402MHz, 2426MHz and 2480MHz respectively.

           

          By the way, have you also fix the crystal warmup issue?

          • 2. Re: BLE radio frequencies incorrect (BCM20736S)
            UdSc_2195666

            Hi boont,

             

            thaks for your reply. The frequencies you mentioned are those we measure if everything works fine. If no communication is possible we measure the frequencies depicted in the following figure:

            frequencies.PNG

             

            ENTRY "PMU Crystal Warm up Time"

            {

               "Crystal warm up time" = 5000

            }

             

            With best regards,

             

            Udo

            • 3. Re: BLE radio frequencies incorrect (BCM20736S)
              BoonT_56

              This is something new! From whom are you getting your module? How many modules are affected by this phenomenon? Do you have a tag3?

              • 4. Re: BLE radio frequencies incorrect (BCM20736S)
                UdSc_2195666

                We're getting our modules from a local reseller from Broadcom. We can't yet say how many of our modules are affected, we have got a couple of feedback from our customers with issues thad could be caused by this phenomenon. While reproduceing this issues in our QC-dept. we have been able to reproduce these issues with only a few devices so far.

                 

                We have a tag3 board.

                 

                With best regards,

                 

                Udo

                • 5. Re: BLE radio frequencies incorrect (BCM20736S)
                  BoonT_56

                  Load the hello_sensor app onto the tag3 and observe what you get on SA. This will form your baseline.

                   

                  Then, load the Hello_sensor app on one of those problematic modules and see what you get.

                   

                  Lastly, load your proprietary application onto the tag3 board and see what you get.

                   

                  Hopefully, this may give some hints as to where could be the issue...

                  • 6. Re: BLE radio frequencies incorrect (BCM20736S)
                    ShawnA_01

                    When you run the MBT.exe utility, what does the spectrum analyzer show you?

                     

                    Make sure you're running SDK 221, as I thought there may have been some RF improvements in it.

                     

                    C:\Broadcom\SDK221\WICED-Smart-SDK\Tools\mbt\Win32>mbt

                    Usage: mbt help

                    Usage: mbt reset COMx

                    Usage: mbt le_receiver_test COMx <rx_channel>

                    Usage: mbt le_transmitter_test COMx <tx_channel> <data_length> <packet_payload>

                    Usage: mbt le_test_end COMx

                    Usage: mbt set_tx_frequency_arm COMx <carrier on/off> <tx_frequency> <tx_power>

                    Check Bluetooth Core 4.1 spec vol. 2 Sections 7.8.28-7.2.30 for details of LE Transmitter and Receiver tests

                    • 7. Re: BLE radio frequencies incorrect (BCM20736S)
                      UdSc_2195666

                      At the moment we use SDK 2.1.1 for our product. Those receiver and transmitter tests you mentioned, we used during the CE / R&TTE certification process and there have been no errors reported so far.

                      After boot up of our device, the advertisements are being sent on the correct frequencies. After a certain time (e.g. over night) we can measure the frequencies mentioned above. Subsequent to a soft- or hardreset of the BCM20736S module the device works correctly for a few hours and so on. This behaviour could only be observed at few of our devices.

                       

                      This behaviour could not yet be reproduced with the tag3 board

                       

                      With best regards,

                       

                      Udo

                      • 8. Re: BLE radio frequencies incorrect (BCM20736S)
                        hachc_2137126

                        Hi,

                         

                          Is there any way to *calibrate* the crystal while it's not so accurate?

                        • 9. Re: BLE radio frequencies incorrect (BCM20736S)
                          BoonT_56

                          We ran past this issue with the developers and it will be fixed in SDK 2.2.2, which is in SVT now.

                          • 10. Re: BLE radio frequencies incorrect (BCM20736S)
                            UdSc_2195666

                            We checked the internal oscillator and could verify the correct oscillator frequencie at 24 MHz. So this seems not to be the problem.

                             

                            With best regards,

                             

                            Udo

                            • 11. Re: BLE radio frequencies incorrect (BCM20736S)
                              hachc_2137126

                              Hi boont,

                               

                                Thanks!

                                But will it be possible for providing calibration tool for setting/trimming the offset of possible non-perfect 24MHz crystal that is used with BCM20737. (We're using BCM20737 + external crystal + external antenna)

                                We found the variant units among our boards manufactured in same process, PCB, components ...etc. Some bad units behave sort of RF issue which cause it failed to be connected by some smart phone (i.e. ASUS android phone), and also with rare successful connection with iPhone.

                              • 12. Re: BLE radio frequencies incorrect (BCM20736S)
                                UdSc_2195666

                                Hi,

                                 

                                in the last days we did some investigation on this issue.

                                 

                                1. We picked ten recent manufactured devices out of one lot and let them send out advertisements every 1 second.  After a short period of time (approx. ½ a day) two of ten devices suffer the same issue depicted in the figure above. This application was built with SDK 2.1.1.
                                2. We programmed the Hello Sensor App out of SDK 2.1.1 into the affected devices. After about ½ a day the devices send out advertisements on wrong frequencies as well, just like they did before.
                                3. Now we programmed the Hello Sensor App out of SDK 2.2.1 into the affected devices. With this application no defective behaviour could be detected after 4 days of operation.
                                4. Lastly we again programmed our Application with SDK 2.1.1 into the devices. And again, the error occurs within a few hours.

                                 

                                • Why does this error only occur at two of ten probed devices out of one lot?
                                • What changes did you make between SDK 2.1.1 to SDK 2.2.1 regarding RF-performance improvements (see shawn's post)?

                                 

                                With best regards,

                                 

                                Udo

                                • 13. Re: BLE radio frequencies incorrect (BCM20736S)
                                  BoonT_56

                                  I suggest that you use the latest SDK (2.2.1) for your work as they have the latest bug fixes reported. The MBT.exe is a package to set the device into HCI mode so that vendor specific commands can be issued to the chip for RF tests. Did you have a chance to review this issue under 2.2.1?

                                  • 14. Re: BLE radio frequencies incorrect (BCM20736S)
                                    BoonT_56

                                    I believed there is a requirement for the 24MHz crystal and this is could be found in the 2073x datasheet. As long your BoM follows closely those recommendations, it should be fine. The reference design has adequate robustness to tolerate some imperfections. If you have a case similar to the above, do open a new submission.

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