5 Replies Latest reply on Mar 19, 2018 10:28 PM by matsubara-y_1534086

    Regarding EZ_Click/MBR3 SNR.

    matsubara-y_1534086

      Hello Cypress.

       

       

      Q1)

      When user measures MBR SNR, should they use Raw count change value(with touch – without touch) as signal value?

      Or should they use Diff count itself as signal value?

       

      I think that user should use Diff count itself when user calculates SNR.

      Because max Diff count(button) is 255 even if Raw count change value is 1000.

       

      But I think that EZ-Click uses raw count change value when EZ-Click calculates SNR.

      If EZ-Click uses raw count even if it is correct to use diff count for SNR, calculated all SNR by EZ_Click may become incorrect.

      Although max diff count is 255, calculated SNR by EZ_Click may exceed 255 depending on the timing.

       

      For example. Please confirm attached pptx file.

      - Noise:                                           3

      - Raw count change value:             560(3560 – 3000)

      - SNR:                                             190

       

       

      Q2)

      Is it OK that diff count saturates(diff is 255)?

      It is difficult to tune so that diff count does not become saturated.

      Because MBR is smart sense and there is only few sensitivity setting.

       

       

      Q3)

      How does MBR3 calculate diff count?

       

      For example, if Raw count change value is 1000(5000 – 6000), does MBR3 compress 1000 and convert it to 1byte of diff count?

      Does MBR3 compress 2byte data and calculate diff count as 1byte?

       

      Or does MBR3 convert 1000 to 1byte of diff count by multiplying by some coefficient(multiply diff by 0.8 etc)?

       

      Or is MBR3 simply subtracting Raw count when MBR3 calculates diff count?

      Then is MBR3 always making diff count 255 when raw count change value exceeds 255?

       

       

      Q4)

      About a graph of “Signal to noise ratio” in EZ_Click.

      SNR from 2nd time becomes lower than 1st SNR.

      Please confirm png file.

      Could you please let us know this reason?

      Does noise in “Signal to noise ratio” also include Raw count change value by finger-touch?

       

       

      Best Regards.

      Yutaka Matsubara

        • 1. Re: Regarding EZ_Click/MBR3 SNR.
          gani

          Hello Yutaka Matsubara-san,

           

          Please go through the following comments;

           

          1) First of all, we would say that the difference in raw counts is not same as difference count in the Ez-Click GUI. The difference count is the normalized form of difference in raw counts multiplied with a normalization factor 'K' (the details are internal to Cypress).

           

          The algorithm measures SNR from the difference in raw counts because as per definition SNR is the ratio of difference in raw counts and the peak to peak noise.

           

          2) Yes. It is ok if difference counts are saturated. This depends on the normalization factor 'k' which is not in the control of user.

          In case of MBR3, for tuning, the user can only adjust sensitivity and thresholds. The recommended finger threshold is 80 percent of the difference count and the recommended noise and negative noise thresholds are 40 percent of the difference count. Please refer page number 82 of the MBR3 CapSense design guide. These percentages are according to difference count but not difference in raw count.

           

          3) The MBR3 multiplies the actual raw count difference with a constant 'K' decided by the algorithm to make the difference count less than 255. More details about this are included in SSHH-131 which is internal to cypress.

           

          4) We are sorry to say that there is a small bug in the SNR window of the Ez-Click GUI. so we recommend you to not to see the SNR values in second and third touch.

           

          Please update if you have any queries.

          Thanks and regards

          Ganesh

          Global Applications

          • 2. Re: Regarding EZ_Click/MBR3 SNR.
            matsubara-y_1534086

            Hello cypress.

             

            Thank you for response.

            I have additional questions.

            Please confirm and answer below questions.

             

             

            Q1)

            Below is description of MBR3 design guide

            --------------------------------------------

            Signal = Raw count – Baseline

            --------------------------------------------

             

            But in actual, above formula is not completely correct.

             

            Correction value(“K”) is multiplied to raw count inside the device.

            The result becomes signal(diff count).

            And internal processing method is confidential.

            So user can not know this internal processing.(how to calculate diff count from raw count)

             

            Is above my understanding correct?

             

             

            Q2)

            >>> The algorithm measures SNR from the difference in raw counts because as per definition SNR is the ratio of difference in raw counts and the peak to peak noise.

             

            I can not understand your comment.

            Why does cypress use not diff count but raw count for SNR?

             

            If button diff count has 2 bytes same as raw count, I can understand your comment.

            But button diff count has only 1 byte.

            Diff count has only 1 byte even if raw count sensitivity is too high exceeding 255.

             

            Assuming the case that difference in raw count is 500 and noise is 100, SNR becomes 5.

            So user decides that their system is OK.

            Because their SNR exceeds 5.

            5 is recommended min value by cypress.

             

            But max diff count is 255 even if raw count is 500.

            If diff count is used for SNR, SNR becomes 2.5 in this case.

            So their SNR can not exceed recommended min value by cypress.

             

            And MBR3 diff count is easy to saturate because there is only few sensitivity setting.

             

            SNR value changes greatly in “Signal” definition.(Raw? Diff?)

            I think that diff count should be used for SNR.

            If raw count is used for SNR, SNR becomes too higher than actual value that MBR3 obtains.

            I think that this is problem.

             

            Please advise it.

             

             

            Q3)

            >>> We are sorry to say that there is a small bug in the SNR window of the Ez-Click GUI.

             

            Is this bug fixable bug?

            Or is it impossible to fix it?

             

            I think that this bug can not be fixed unless Ez-click GUI changed significantly.

            Because I think that it is difficult that Ez-click GUI decides whether difference in raw count is due to finger-touch or not(noise, temp ,etc).

             

            Please comment it.

             

             

            Best Regards.

            Yutaka Matsubara

            • 3. Re: Regarding EZ_Click/MBR3 SNR.
              matsubara-y_1534086

              Hello Cypress.

               

              Can you update this community?

               

              And I have additional question.

               

              Q4)

              Is there a way to acquire log data of Raw, Base and Diff simultaneously using EZ_Click?

              If EZ_Click does not have a way to obtain these log data, should user use BCP to obtain log data?

               

              Best Regrads.

              Yutaka Matsubara

              • 4. Re: Regarding EZ_Click/MBR3 SNR.
                gani

                Hello Yutaka Matsubara-san,

                 

                 

                Q1) We would like to say that Signal and difference count are quite different. Difference count value is normalized version of Signal. User cannot know the internal processing or the value of 'K'.

                 

                Q2) The difference count is calculated from the formula diff count = (Raw counts - Baseline) * K. This means that the difference count is the normalized value of signal. As per the definition of SNR, SNR is the ratio of Signal and peak-to-peak noise. So we are not modifying the value of SNR. The diff count is normalized with 'K ' to make the setting of various thresholds easier. For example if the diff count is below 255 it will be easier for the user to set the finger threshold i.e. 80% of difference count and noise threshold as 40 % of difference count.

                 

                Q3) The bug is fixable. But as you said we need to work with Ez-Click GUI dsign team to make the changes in it.

                 

                Q4) Sorry. We do not have option to log the data in Ez-Click. You can use the bridge control panel and read the corresponding registers to do that.

                 

                Thanks and regards

                Ganesh

                • 5. Re: Regarding EZ_Click/MBR3 SNR.
                  matsubara-y_1534086

                  Dear Ganesh-san.

                   

                  Thank you for your response.

                   

                  Are there any plans to fix EZ-click bug(SNR window)?

                   

                  Best Regards.

                  Matsubara / Macnica