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CAPSENSE™ & MagSense

jcsb1994
Contributor

Hi all,

I have a 2-layer PCB using a Capsense CSX touchpad, following the capsense design guidelines as much as possible

jcsb1994_0-1621459208730.png

The touchpad is in the blue circle, and as you can see no circuitry at all is under it, as advised in the documentation.

Now, I have a space critical application where I would need the PCB to be the size of the touchpad, so I need all of the circuitry behind it.

1. Is it possible to do so without introducing too much noise in the sensors?

2. Of course, I would use a 4-layer PCB. What would be the ideal layer stack to minimize noise. Maybe a hatched ground in one of the internal layers?

Thanks a lot! have a nice day.

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1 Solution
ncbs
Moderator
Moderator

Hi @jcsb1994,

Yes, it is possible to have the components (other circuitry) present in other layers (behind the trackpad). A hatched ground layer is required to keep down the noise levels from disturbing the CapSense sensors. This needs to be present in between the sensor layer and the "other circuitry" layer.

Regards,
Nikhil

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3 Replies
ncbs
Moderator
Moderator

Hi @jcsb1994,

Yes, it is possible to have the components (other circuitry) present in other layers (behind the trackpad). A hatched ground layer is required to keep down the noise levels from disturbing the CapSense sensors. This needs to be present in between the sensor layer and the "other circuitry" layer.

Regards,
Nikhil

View solution in original post

jcsb1994
Contributor

Thank you, I pretty much have my answer at that point, but is there a design document I could refer to for this specific application? Thanks again

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ncbs
Moderator
Moderator

Hi @jcsb1994,

There is no exclusive document speaking about this specific application.

However, PSoC4 and PSoC6 Design guide speaks about the general rules and recommendations. To reiterate:  

  • Section 7.2 deals with sensor construction and speaks about having a simple design of only 2 layers 
  • Section 7.4.2 speaks about different layers present in a CapSense system
  • It is advised to have switching signals as far away from the CapSense traces as possible. Crosstalk solutions (7.4.8) deals with this.
  • Section 7.4.10 lays down general guidelines of GND plane and 7.5.3.2.1.1 speaks about reducing noise using a GND plane. Section 7.5 speaks about various noise sources affecting CapSense system and prevention methods.

 

Hope this helps,
Nikhil