I am working on a 24+2ends segmented slider, and would like to Diplex it. I am concerned about the Cp of the segments in a diplexed configuration. I am also curious about increasing the segment height to 20-24mm, so the user has a better chance of hitting the slider that will be hidden under a wood overlay(85mm wide) with no outside visual indication the slider is beneath.
Device is PSOC 4000S - CY8C4024LQI-S412
My traces are 0.16mm wide and are an average of 120mm long total for each diplexed channel.
Slider segments are 8mm wide and 15mm in height using H/4 rule for the dual chevron and .5mm spacing as per datasheet.
4 layer FR4 1.2mm thick
3m 468MP for adhesive
1.2mm wood overlay oil/wax finish.
Should I be concerned about what I am attempting to do? It looks like the 4000s series is able to accommodate 200pF of sensor capacitance each channel will surely fall in that range.
I dont see any issues with your current design plan.You have done your design as per our recommendation in documents.
On the question about increaing the slider height, the increase in height will lead to increase in Cp which might affect the slider performace.So i suggest you to follow our recommendation which we have tested.
Also please have a provision to have a shield connected to hatched ground around the slider,which will help in tuning and increasing the perdomance of slider if needed as per your design.
My stackup is
Top Layer - MCU and traces with seperate hatched ground at slider
Inner 1 - Ground with seperate hatched ground at slider connected to Epad Vias
Inner 2 - Ground and diplex jumpers with seperated hatched ground at slider
Bottom - Ground and slider with seperate hatched ground at slider
Should I be adding the 1cm driven shield around the slider just on the bottom layer?
AN85951 Page 131 - suggests that the layer adjacent to the slider should have its hatch connected to the driven shield but it does not specify how much of that hatch should be connected.
Attached are my layers.
I recommended to have a provision for shield connection to hatched pattern, just so that if you are not able to get the required performance we can use it to increase the performance.
Please have hatched ground around the slider sensors and a provision to connect to shield.
First measure the performance using the pattern connected to Gnd and if it doesn't meet the requirements then you can connect the pattern to shield and do the measurements.
It is recommended to have hatched gnd on the sensor layer and the layer beneath it and provision to connect both these to shield.