Capacitors in touch screens, parallel or series?

[Elvislaur]

Homework Statement

Hi, I'm trying to find out are the capacitors in mutual capacitance touchscreens are in series or in parallel. I'm very confused because they're asking me what would happen if they were in parralel or in series?

maybe in mutual capacitive touch screens they're in series and in self capacitande-in parallel as shown in http://electronics.howstuffworks.com/iphone2.htm pictures..

 

[berkeman]

Homework Statement

Hi, I'm trying to find out are the capacitors in mutual capacitance touchscreens are in series or in parallel. I'm very confused because they're asking me what would happen if they were in parralel or in series?

maybe in mutual capacitive touch screens they're in series and in self capacitande-in parallel as shown in http://electronics.howstuffworks.com/iphone2.htm pictures..

Homework Statement

Homework Equations

The Attempt at a Solution

Do you mean the capacitance at each crosspoint between the Driving and Sensing lines? Why would those capacitances be in series?

 

[Elvislaur]

Do you mean the capacitance at each crosspoint between the Driving and Sensing lines? Why would those capacitances be in series?

Now I'm getting an idea why they're in parallel, but why they're asking me to discus what would be if they would be in series? Cuz every crosspoint actually is like a capacitor.

 

[berkeman]

You used the terms "mutual capacitance" and "self capacitance" in your original post (OP) above. I hadn't seen those terms before, so I looked them up on wikipedia.org.

The mutual capacitance is the normal capacitance we think of between two conductors (like plates of a capacitor, or the capacitance at the crosspoints of the touchscreens). The "self" capacitance is the capacitance of a single conductor to all other objects around it. Like the capacitance of a person standing in a room.

I don't quite get yet the use of these terms in touchscreen applications yet (I guess I need to do more reading). My impression of the touchscreen sensing was just that putting your finger over the driving line helped to increase the capacitive coupling of the driven signal into the sense line.

Does your reading of the link and other wikipedia/other articles suggest some other mechanism?

 

[Elvislaur]

I've been reading a lot about this unfortunately there is not much info about latest capacitive touchscreens, but as far as i understand this now that there are two tipes of capacitive touch screens: Self capacitive and mutual capacitive, first one recognises only one touch at the same time like mine Xperia x10 and scnd is multi-touch like all iPhones with parallel capacitors..

I guess they want me to mention about resistive touch screens which are with resistors in series, but its another story without capacitance!