Probing capsense and shield signals

[Anonymous]

Hey guys,

   

I'm working on a product with a proximity sensing loop, and a driven shield on the backside to direct sensitivity in a single half of the pcb plane.

   

I'm trying to figure out if my CMod capacitor is sized properly for my application. Here's a scope capture, Chan1 is the sensor signal, and chan2 is the driven shield. Is this what it is supposed to look like?

       

The application notes and reference manuals said to 'make sure CMod is fully charging and discharging' but it didn't specify what the voltage is or what the waveform should look like--so guidance is appreciated.

       

[Image attached] also uploaded here: http://i.imgur.com/DlMw2Xy.png

[Bob_Marlowe]

Welcome in the forum.

   

Probing in the pF range can easily destroy your signal. Why don't you try the tuner application to check for proper signal discovery. It even allows for applying changes on-the-fly to your CapSense components. What value is your CMod?

       

Bob

[Anonymous]

Ah, I was afraid of that. 

   

I'm using the EZ-BLE module at the moment, which has a cmod of 2.2nF and ctank of 10nF.  

   

In the tuner I see a reasonable signal swing, is there anything else to check in there that would confirm whether cmod is large enough?

   

Thanks!

[Bob_Marlowe]

You may configure your CapSense, so that you can modify the properties from tuner. Not only set for sensitivity, but set the noise margin and the hysteresis which are all affected by your electrical and geometric configuration of the final product.

       

Bob