3 Replies Latest reply on Oct 26, 2017 11:38 AM by gani

    Regarding capsense layout.

    matsubara-y_1534086

      Hello.

       

       

      Q1-A)

      Below is description of P116 in AN64846.

      -> http://www.cypress.com/file/41076/download

      =========================================

      Air gap to ground and other sensors should be equal to the overlay thickness, but no smaller than 0.5 mm, and no larger than 2 mm.

      The spacing between the two adjacent buttons should be large enough that if one button is touched, a finger should not reach the air gap of the other button.

      =========================================

       

      Which part of layout does the above explain?

      Which ‘A’ or ‘B’ of attached file does the above explain?

       

      I think that above explains ‘A’ of attached file.

      Because I think that “Air gap to ground” of document is pointing to ‘A’.

       

      But I do not know what “other sensors” explains.

      Does “other sensors” explain the spec of gap between sensors?(like ‘B’ attached file)

      If yes, I can not understand the meaning of “no smaller than 0.5 mm, and no larger than 2 mm”.

       

      I think that any issue will occur if the gap between sensors is too close.

      In this time, I think that the possibility of false touch will increase.

       

      But I think any issue will not occur if the gap between sensor is too far.

      So I could not understand a sentence of “no larger than 2 mm” if “other sensors” of above explanation points a gap between sensors.

       

      And layout checklist explains “Air gap between button and hatch”, but checklist does not explain “other sensors”.

       

      Please advise about above explanation.

       

       

      Q1-B)

      What kind of a problem occur if above spec of user’s layout is smaller than 0.5mm?

       

      Will parasitic capacitance increase because GND approaches the sensor?

      Then will sensitivity decrease?

       

       

      Q1-C)

      What kind of a problem occur if above spec of user’s layout is larger than 2mm?

       

      Will noise immunity weaken because GND leaves the sensor?

       

       

       

      Q2-A)

      Below is description of P117 in AN64846.

      =========================================

      Keep the width less than or equal to 7 mil (0.18 mm)

      =========================================

       

      Does above description explain trace width of ‘C’ in attached file?

       

       

      Q2-B)

      What kind of a problem occur if above spec of user’s layout is bigger than 7mil(0.18mm)?

       

      Will parasitic capacitance increase?

      Then will sensitivity decrease?

       

       

       

      Best Regards.

      Yutaka Matsubara

        • 1. Re: Regarding capsense layout.
          gani

          Hello Yutaka Matsubara-san,

           

          Please find the comments below:

           

          Q1-A) The image shown in the attachment is not very clear. Also it is not 'A'. Please note that the air gap means the open space between the CapSense sensor and the surrounding hatch pattern. Please refer pages 80 and 87 in the application note you mentioned for more understanding.

           

          Another important thing is there should be enough gap between sensor to sensor. This includes the hatch pattern present in between the sensor and sensor. The ideal diameter of finger touch is 8mm. So if the gap is less than 8mm, the finger might touch other sensor when you touch one sensor. This may result in false trigger. This is properly represented by 'B'.

           

          Q1-B) Yes. You are correct. When the ground approaches the sensor the parasitic capacitance will increase and the sensitivity will be decreased.

           

          Q1-C) When the gap increases more than 2mm the effect of having ground hatch around the button sensor will be decreased and the noise impact will come into picture.

           

          Q2-A) Yes. You are correct. 'C' represents the width of the trace.

           

          Q2-B) When the width of the trace increases more than 7 mil, the parasitic capacitance will increase and the sensitivity will decrease. Also since the thickness is more the traces will act as CapSense sensors sometimes. This may lead to false trigger when traces are touched..

           

          Please update in case of any queries.

           

          Thanks

          Ganesh

          • 2. Re: Regarding capsense layout.
            matsubara-y_1534086

            Dear Ganesh-san.

             

            Q1-A)

            What part of the document(001-64846) did you explain?

            It seems that P80 and P87 are not related to this question.

             

            This question is about below description.

            =========================================

            Air gap to ground and “other sensors” should be equal to the overlay thickness, but no smaller than 0.5 mm, and no larger than 2 mm.

            =========================================

             

            I think that “Air gap to ground” is a spec of left figure of attached file(between edge capsense pattern and GND hatch)

            And it is the same as ‘A’ of customer’s layout.

            Is my understanding correct?

             

             

            But I have one question in this case.

             

            I do not know what “other sensors” explains.

            Does “other sensors” explain the spec of gap between sensors?

            If yes, I can not understand the meaning of “no smaller than 0.5 mm, and no larger than 2 mm”.

             

            I think that any issue will occur if the gap between sensors is too close.

            In this time, I think that the possibility of false touch will increase.

             

            But I think any issue will not occur if the gap between sensor is too far.

            So I could not understand a sentence of “no larger than 2 mm” if “other sensors” of above explanation points a gap between sensors.

             

            And layout checklist explains “Air gap between button and hatch”, but checklist does not explain “other sensors”.

             

            Could you please let us know which parts does “other sensors” explain.

             

             

            Best Regards.

            Yutaka Matsubara

            • 3. Re: Regarding capsense layout.
              gani

              Hello Yutaka Matsubara-san,

               

               

              Good day to you !! Please find the comments below.

               

               

              >>"What part of the document(001-64846) did you explain?

              It seems that P80 and P87 are not related to this question."

               

               

              Cypress--> Sorry for being unclear. I am trying to explain about the air gap requirement between the CapSense sensor and surrounding hatch pattern. I have refered page 80 and 87 which shows the airgap

              between the capSense sensor and surrounding hatch qualitatively.

               

               

              >>"I think that “Air gap to ground” is a spec of left figure of attached file(between edge capsense pattern and GND hatch)

              And it is the same as ‘A’ of customer’s layout.

              Is my understanding correct?"

               

               

              Cypress--> Yes. You are correct.

               

               

              >>"I do not know what “other sensors” explains.

              Does “other sensors” explain the spec of gap between sensors?

              If yes, I can not understand the meaning of “no smaller than 0.5 mm, and no larger than 2 mm”.

               

               

              Cypress--> Please do not misunderstand. The intension is not the one actually written in that sentence. The word "other sensors" mean all the sensors and it doesn't mean between sensor to sensor distance.

              Please note that we recommend the minimum gap of 8mm between button sensors because there is a chance of false touch when the buttons are too closer. The 8mm came from the average

               

               

               

               

              >>"But I think any issue will not occur if the gap between sensor is too far.

              So I could not understand a sentence of “no larger than 2 mm” if “other sensors” of above explanation points a gap between sensors."

               

               

              Cypress--> Yes. There will not be any issues if the buttons ate too far. In fact we recommend to keep the buttons as far as possible.

               

               

              Kindly update if you have any queries.

              Thanks and Regards

              Ganesh